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Mustang EFI Information



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1986-1988 computers:  The 1986 thru 1988 Mustang 5 liter cars were equipped with a speed density fuel injection system.  This system was ditched in favor of the mass air system in 1989 and 1988 on stricter emmisions California Mustangs.  The mass air system is much more performance modification friendly.  Speed density cars can be modified but are very sensitive to camshaft selection.  You are restricted to either the stock cam or maybe a very mild aftermarket cam that doesn't have much more duration and overlap than the stock cam.  Pretty much everything else can be modified to an extent.  Cylinder heads, intake manifolds, rocker arms, throttle bodies, headers and underdrive pulleys can all be upgraded.  If you buy a Mustang that falls into the 1986 to 1988 year bracket, be sure to check to see if it has a mass airflow sensor.  If the car is a 1988 model year, it could be a California model that was factory equipped with the mass air system.  It is also possible that one of the previous owners replaced the speed density system with a mass air system.  This was a common conversion and there are many aftermarket companies that make adapter harnesses and full kits for this conversion.  So make sure you check your car out to see what system you have.

1989-1993 computers: You can use either the A9L or A9P in a five speed fox body mass air car. Some say the A9P has a slightly aggressive spark and fueling tables and does not retard timing between shifts and the A9L does but I have no verification on that.  The A9L computer came in 1989-1993 5 liter-manual transmission Mustangs.  The A9P computer came in 1989-1993 5 liter-automatic transmission Mustangs.  The A9S came in 1988-1993 California emissions Mustangs.  The X3Z computer came in all 1993 Cobra Mustangs.

1993 Cobra X3Z:  X3Z 1993 Cobra computer has modified fuel tables for the 24lb injectors used on the Cobra engines.  Factory mass airflow sensors are not "calibrated" that is an aftermarket thing. All factory mass airflow meters tell the computer how much air is coming into the engine and that is it.  They do not tell the computer what injectors are in the engine.  The X3Z Cobra computer timing curve is not as aggressive as the A9L an A9P units and also has a speed limiter.  The reason for this was to detune the Cobra engine for drivetrain durability (warranty issues).  The X3Z Cobra computer also has poor idle issues as well as hesitation issues associated with it. 

1994-1995 computers:  The TM40’s (94-95 GT computer) processor runs 3x the clock speed of the fox body processor and is based off of Volumetric Efficiency (VE) The TM40 also many more parameters to tune with but also has many built in timing retards that need to be addressed which is the main reason why 1994-1995 Mustangs are slower than a comparable fox body Mustang.  In 1994 Ford did a major redesign of both the computer hardware and software which resulted in a smoother running and more emissions friendly car.  These computers are more sensitive to modifications than the pre-1994 computers.  Although the 1994-1995 Mustangs made the same horsepower on the dyno as fox body Mustangs but once you put the engine in the car things change.  In the 1993 and older computers the spark advance at wide open throttle was based on engine RPM only. At wide open throttle the computer jumped to a separate spark function that Ford thought was the best spark curve. Everytime you go to wide open throttle in a 1993 or older car, you run pretty much the same spark curve run after run. In the 1994 - 1995 cars the wide open throttle spark function was deleted and computer uses the same spark tables for both part throttle and wide open throttle spark calculations. The  spark table is based on RPM and engine load and the computer uses the mass airflow sensor to determine load. Any change in the calculated load will effect how much spark advance you get. Since the computer uses the mass airflow sensor to calculate load, changing the mass air flow sensor will change the load calculation. Changing the cam, heads, etc will also effect load. It is possible when upgrading the mass airflow sensor, heads, etc. the computer will remove timing resulting in an instant loss of horsepower.  The loss in horsepower can be at any rpm or all rpm.  In other words, anything that effects airflow into the engine will also have an effect on the spark advance and probably a negative effect.  Another issue with the 1994-1995 T4M0 computers is spark retard during shifts.  The automatic cars seem to pull more timing out than the manual transmission cars.  This is due to the tip in retard in the T4M0 computer.  When the throttle is moved from closed to an open throttle position (such as shifting a 5 speed car or passing on the highway) the computer will retard timing.  The amount of spark retard varies but the computer can retard the timing as much as 15 degrees during shifts.  This results in a loss of horsepower which is really why this feature is was programmed in the computer in the first place.  Plain and simple doing this reduces power and is less damaging to drivetrain parts such as the transmission.  Everyone knows how weak the factory transmissions were in Mustangs.  Likewise with the automatic transmissions the computer retards the timing when it thinks its time to shift.  The result is sloppy shifting and a slower car.  A shift kit will make these transmissions shift firmer by manipulating fluid pressure in the transmission but the spark retard function in the computer will still be there. The solution for these issues is tuning.  A device such as an SCT chip can remove all of these issues.  The TM40 is a much better computer than the A9L, A9P and other fox body computers but it needs some tuning and tweaking to work optimally. 

1994-1995 Cobra J4J1: This computer like the X3Z 1993 Cobra has modified fuel tables for 24lb injectors. The 1994-1995 Cobra also uses the same mass airflow sensor as the 1994-1995 GT.   

86-93 Mustang idle issues: Idle issues are common on these cars, especially 5-speed cars.  EGR Valves, Idle Air Bypass solenoids and Throttle Position Sensors are common causes. A bad connection with the 10 pin (salt and pepper shakers) black and white engine electrical connectors can also cause poor idle quality.  To ensure a good connection on the 10 pin connectors a little modification can be done which is fairly easy and will cure some surging and hanging idle issues on 86-93 Mustangs and should be the first thing done when tackling any idle issues.

10 Pin Connector modification:

1. Take the 10 pin connectors apart (salt and pepper shakers).

2. use a pick like tool to spread the male terminals open more so they make better contact. In the center of each male terminal there is a small seam and seams down the sides of the terminal which allows you to spread them open.

3. Apply some dielectric grease to the terminals

4. Plug the connectors back in.


Throttle Position Sensor (TPS) adjustment:

Without the proper adjustment, the throttle position sensor (TPS) will give the computer false reading as to the exact throttle opening. A false reading will limit wide open throttle performance. A voltage reading must be taken using a digital volt/ohmmeter (DVOM) with the Key On/Engine Off and with the Key On/Engine Running.

The TPS is located directly on top of the throttle body and is adjusted by loosening the two phillips mounting screws and swiveling the sensor until the highest reading is found. It may be necessary to elongate the holes with a small drill bit or small file to achieve the desired reading. The spec range for Key On is from .88 to 1.0 volt; shoot for the .90 to .98 volt. Make sure voltage reaches/exceeds 2.71v at WOT.

Incorrect Throttle Position Sensor (TPS) voltage will result in reduced performance including a possible hanging/surging idle. The best way to take a TPS voltage reading is by using two safety pins through the wires coming from the sensor. The positive lead is attached to the green wire, while the negative goes to the black wire. Always ground the meter through the sensor's black wire. This gives a direct, and more
accurate ground into the computer.




Resetting the base idle:

  1. Clear the computer's idle memory by disconnecting the battery for 20+ minutes.

  2. Disconnect the Idle Air Bypass solenoid
  3. Reconnect battery
  4. Start engine and set idle speed to desired RPM with idle screw on throttle body
  5. Turn off engine and reconnect the air bypass solenoid
  6. Set TPS voltage between 0.90 - 0.95 volts with a digital volt meter
  7. Start engine and let it idle for 2 minutes with no accessories on.
  8. Turn off engine for two minutes
  9. Start engine again and run for 2 minutes with every accessory turned on.
  10. Turn engine off again.



Distributor phasing on EFI Mustangs:

EFI Mustangs use Sequential fire injection which means the injectors are triggered by the PIP signal that is generated by the stator signal.  The PIP signal uses the #1 cylinder id pulse to keep the fuel on time during the intake stroke and fires the rest based on the firing order.  Distributor installation not only times the spark to the cylinder but also times the fuel injectors.  If the distributor is installed with the rotor not pointing toward the #1 plug on the distributor cap the rotor will be out of phase.  This will cause a timing error of the fuel injectors resulting in a less than optimal fueling pattern which will affect performance.  The engine will start and run and might not have any noticeable problems but performance will suffer. 


What effects does incorrect rotor phasing have on performance?  Imagine installing the distributor with the rotor pointing toward the terminal directly to the left of the #1 terminal (which would be #3 cylinder).  This will advance the firing order similar to rotating the distributor but what’s different is the fuel injector timing will start advanced and will be spraying fuel at a closed intake valve.  Some fuel will evaporate before the valve opens again which will cause wasted fuel and destroy atomization.  This will have an affect on performance and fuel economy.  The EEC-IV system's Adaptive Strategy will see a lean codition from the Oxygen sensors, and will force the system to compensate by increasing injector pulse width. The computer doesn’t know you installed the distributor incorrectly, so it is trying to ensure an air/fuel ratio of about 14.64:1 which is going to cause more fuel to be injected by the fuel injectors at the wrong time.  This is going to waist more fuel and further reduce performance. 


This is the proper way to install the distributor in a 5 liter EFI Mustang:

1. Remove the passenger side valve cover.

2. Turn the engine over until 0 on the balancer is lined up with the timing pointer.  You might have to clean the balancer and timing pointer.  This is a good time to clean them up anyway.  It is also a good time to mark the 10, 12, 14 and 16 degree marks on the balancer with a white paint marker.

3. Verify that both the intake and exhaust valves on the #1 cylinder are closed and then reinstall the valve cover.

4. Install the distributor with the rotor pointing toward #1 on the distributor cap.  When installed correctly the rotor will be pointing slightly to the left of the center of the engine and the TFI module will be pointing to the right of center of the engine.  The cap adapter mounting screw toward the engine will be facing the center of the engine.

5. Start the engine and let it warm up to operating temperature.

6. Remove the spout connector.

7. Use a timing light and set the initial timing to where you want.  10 degrees is the stock setting but 14-16 degrees adds a slight performance gain.

8. Tighten the distributor clamp and verify the timing one more time.

9. Plug the spout connector back in.

10. Check the timing with the spout plugged in to verify the computer is controlling the spark advance.  You’re finished!


Dry and Wet Nitrous system info:

I guess the first thing to clarify is "dry" when talking about nitrous oxide kits refers to the fuel being introduced separate from the nitrous. In other words the fuel and nitrous are not mixed together like in traditional nitrous systems. Dry does not mean no fuel or lean or anything else. It simply means the nitrous is injected separately from the fuel. Carbureted intake manifolds are designed to flow air and fuel so nitrous plate system really have no major issues with carbureted applications. However, EFI intakes are designed to flow air and air only. This presents problems when using traditional "wet" nitrous systems. Most EFI intakes have long runners, dips and valleys where fuel could potentially "puddle" and create a major backfire. This problem is typical with wet systems that use a plate that is sandwiched between the throttle body and intake and also wet systems that use a nozzle mounted in the intake or the air inlet tube before the throttle body. The problem doesn't seem to be as common with wet systems that use a plate that is mounted between the upper and lower intake.

EFI fuel pressure regulators work on a 1:1 ratio with fuel versus air pressure. That means placing 1 lb of pressure on the vacuum line to the fuel pressure regulator will increase fuel pressure by 1 psi. A dry nitrous kit uses a reduced amount of nitrous pressure to increase fuel pressure via the fuel pressure regulator. Since nitrous bottle pressure is usually 900-1000 psi it needs to be reduced because 900-1000 psi is obviously too much fuel pressure and will cause a plethora of problems. Dry kits use a T with a restriction or jet inside in the line from the fuel pressure regulator that connects the fuel pressure regulator with manifold vacuum at one end and nitrous oxide pressure at the other end. This way the regulator will function normally when the nitrous system is not being used. A larger jet or restriction in the T will create less fuel pressure while a smaller jet or restriction will create more fuel pressure which is opposite of traditional nitrous jetting...something to keep in mind when tuning a dry system.
With a dry system there is no risk of fuel puddling backfires like there is with wet systems and you don't have to plumb fuel lines for a fuel enrichment since the fuel injectors handle the fuel demands. Dry systems start off rich and then bring the nitrous in to lean the mixture out to where it needs to be. Wet systems can sometimes start lean and then go rich because the nitrous is under alot higher pressure than the fuel is so nitrous will usually get to the engine before the fuel does. Dry systems don't come on as hard from the start as wet systems do which can be beneficial for off the line traction. There are some drawbacks to dry nitrous systems though which are not very common. There have been a few cases of the rubber fuel rail connecting lines rupturing. I don't think this is an issue with the NOS-05115-II kit because the fuel pressure only spikes to about 80-90 psi but other kits that are designed differently see fuel pressure spikes as high as 125 psi. This line rupturing problem could also happen if with worn or rotted rubber hose. There can be cylinder distribution problems with dry systems. The fuel itself is pretty equal cylinder to cylinder but nitrous distribution problems can occur do to distribution issues with intake manifolds. Some cylinders might be rich while others might be lean. However, even carbureted plate systems for Fords have this issue. Most noteably with #1 and #5 cylinders. Chances are most people won't have any negative issues with distribution unless they start messing with custom nitrous tune ups involving larger amounts of nitrous.

I'm a big fan of the Nitrous Oxide Systems NOS-05115-IINOS kit. The kit is very reliable and user friendly. I feel it is the safest nitrous system on the market and I haven't heard anyone else say otherwise. The kit comes with all of the necessary components and an inline high flow fuel pump and has several safety features built in. It costs more than most other Mustang nitrous kits but as the old saying goes, "you get what you pay for". Nitrous Oxide Systems (NOS) has been researching and developing Mustang EFI dry kits since the first EFI Mustangs rolled out of the Ford plant. The NOS-05115-IINOS kit incorporates a Hobbs switch (fuel safety shut off switch) which does not allow the nitrous system to activate until fuel pressure is above 55 psi and also shuts the nitrous system off in case of a drop in fuel pressure. The NOS kit also comes equipped with two nitrous solenoids which both need to open before nitrous oxide will be injected into the engine. When the first one opens it sends a signal to the fuel pressure regulator which then raises the fuel pressure. Once the fuel pressure gets to 55 psi, the Hobbs switch will open the second solenoid which will then inject the nitrous into the engine. Most other kits don't have this feature. The NOS kit also uses two jets, one for nitrous and one in the bleed off T where most other kits have a fixed restriction for a bleed off hole instead of a jet. Having a fixed restriction means you can not tune the fuel pressure like you can with the NOS brand kit so as you increase the nitrous jet size you are leaning the system out and have no way to add fuel to compensate. Another benefit to the NOS kit is by design if the bottle pressure is decreased (due to temperature, bottle getting empty, etc.) the amount of fuel pressure is also reduced. This is due to the nitrous pressure regulator that NOS uses with this kit. Most other brands don't have this feature because the kits are simpler in design, hence the cheaper prices. Most of these other brands also have a pretty harsh initial fuel spike that is high enough to burst the rubber hose that connects the fuel rails. NOS offers two versions of this kit. The NOS-05115NOS kit is a non adjustable 75hp nitrous system. NOS does make an upgrade kit for this kit which converts it to an adjustable kit up to 150hp. The part number for the upgrade kit is NOS-0016NOS. NOS also makes a Stage II kit which is adjustable from 75-150hp and comes with an inline high flow fuel pump. The part number for this kit is NOS-05115-IINOS. You can get creative with these kits just like any other nitrous system. As the kits stands, it will support 175hp. With the addition of larger fuel injectors, larger nitrous solenoids, larger nitrous nozzle line (to replace the small -3 line) and larger nozzle, 300+ horsepower has been made with this kit.

Other info about this kit. Recently NOS has gone to the fixed T design with a .42 orfice and is non adjustable but is designed to work with all horsepower levels that the kit was originally intended for. This was due to production costs as well as liabilities. The solution to this is to find an older adjustable T from a parts store, classifieds or Ebay. Also, if you run more than 1000 psi bottle pressure you can damage the internals of the nitrous pressure regulator and cause it to not work. With a dry kit, make sure your injectors are big enough for your overall horsepower level otherwise your engine won't get enough fuel. It is also important to keep fuel pressure below 100 psi because typical fuel injectors will lock open above 100 psi. The solenoids of the NOS dry kit will only support 175hp.



EGR – Many misconceptions here.  Removing the coolant lines from the EGR spacer will increase the intake temperature, not reduce the temperature.  Engine coolant is 180-196 degrees, exhaust temperature is about 1000 degrees.  Do the math.  I don’t know why so many people can’t figure this out and think the lines are “hot coolant lines”.  The coolant lines cool off the EGR spacer which then reduces the air intake temperature, thus the reason they are called “coolant lines”.  Pretty simple concept….  Another thing people like to do is remove the EGR valve from the spacer and use a block off plate.  Doing this really gains you nothing besides maybe some hotter combustion chamber temperatures and an increase in NOx emissions and the possibility of detonation.  For the average Mustang enthusiast, removing the EGR is a waste of time.  The EGR valve only opens at part throttle.  At idle and wide open throttle the EGR valve is closed.  Removing the EGR and spacer will reduce intake temperatures but will require an EGR spacer delete plate such as the ones available from Accufab.  This is a 3/8” thick plate that goes in place of your EGR spacer and has a provision to mount your throttle cable.


Thermostats – Some people think they are going to make some serious horsepower gains by installing a 160 degree thermostat or by not running any thermostat at all.  This is simply not true.  Installing a 160 degree thermostat on an EFI car will richen then mixture but will keep the computer in “warm up” mode which will have more conservative timing curves and will also never enter closed loop mode.  If the coolant temp stays below 170° for too long in a drive cycle, code 21 is logged and open loop is forced. You can correct this with a chip and tune by changing the minimum ECT under running conditions.  In closed loop mode the computer uses feedback from the oxygen sensors to fine tune the mixture.  Other problems associated with a low operating temperature is catalytic converter damage and increased cylinder wear.  If you are changing thermostats, don’t use anything less than a 180 degree thermostat.


Aftermarket throttle body whistling – Check the alignment of the idle air bypass solenoid and the throttle body.  If the two holes on the throttle body don’t line up with the two holes on the solenoid you will get a whistling noise, especially at idle.  A little bit of work with a die grinder or dremel tool to make the holes line up will cure this whistling problem.


Another throttle body whistling can be attributed to a partial opening and the IAC reaching its idling gap. If this is the issue, you will need to do the following:

1. Get a 1/16" drill and open an IAC bypass hole on the TB blade LH half or farthest away from the IAC transfer hole.

2. do a base idle reset



Smog pumps – Not much to be gained by removing a smog pump.  At wide open throttle the smog pumps discharge is dumped to the atmosphere rather than being pumped into the exhaust which requires significantly less horsepower than pumping it thru piping into the exhaust.  The performance gain is minimal at best.  Don’t bypass the smog pump and expect to see any new found horsepower.  Taking the pump and AIR system off for weight reduction makes more sense.  One thing I have found over the years is on 87-93 Mustangs the smog pump can cause popping in the exhaust on deceleration when using an off road H-pipe or X-pipe (no catalytic converters).  I have run into this issue a few times and bypassing the smog pump has cured the problem every time.  One thing to keep in mind if you bypass your smog pump is the bearings tend to seize in the pump if it goes for a long period of time with no use.  So if you bypass the pump and expect to use it again in 8 months, you might end up with a seized pump.


Fuel pressure – Increasing fuel pressure on a stock or “bolt on” Mustang is going to do more harm than good.  Everyone thinks bigger is better but that is rarely the case with anything.  When you increase your fuel pressure the EEC will reduce the injector duty cycle because the oxygen sensors will tell the EEC that the engine is running rich.  Even worse, the EEC could get confused enough and go into limp mode causing the car to run poorly.  On stock or close to stock Mustangs there is actually a benefit to reducing the fuel pressure to about 28-30lbs.  This is typically worth about 4-5 horsepower across the entire rpm range.  Once again, bigger is not always better.  Don’t increase fuel pressure unless the engine requires it.  Removing the vacuum line is not a good idea either.  All you are doing there is raising the fuel pressure at idle and part throttle without changing it at wide open throttle.  This will get you some worse fuel economy and most likely worse performance. 


Performance chips – These commonly available chips (Hypertech, Superchips, etc.) are a waste of time.  Other chips out there are often referred to as “can tunes” and are nothing more than a mail order tune package where a company or individual tunes your car over the internet and sends you a chip to install.  “Can tunes” as some are called are of questionable benefit.  If you want to do any tuning with a chip, go to a reputable tuner that has a dyno and tune the right way.



Factory Mass Air and Speed Density system information

Most people have the opinion that you can not modify a factory speed density car whether it be a Mustang, Lincoln or any other vehicle because it will "run like crap".  Another one I've heard is a modified factory speed density car will run too lean and melt the engine down.  Its common to hear "speed density sucks" also.  All of these opinions are just that, opinions.  None of it is fact.  Speed density cars run well when modified.  The major issue is with camshaft selection.  The factory speed density system runs off of vacuum and has a predetermined idle vacuum amount and with more duration than a factory camshaft manifold vacuum at idle is reduced.  This causes a surging or hunting idle and stalling.  At all other throttle positions the car will probably run normal.  There are camshafts out there that claim to work with speed density but the factory camshaft is not a bad camshaft to work with in mild applications.  The factory speed density computer can not measure airflow and can not compensate for big airflow increases so you are somewhat horsepower limited.  Chances are if you are using a factory speed density system it is going to be a mild application anyway.  You can run aftermarket cylinder heads, intake manifolds, headers, throttle bodies and injectors with the factory speed density systems as well as superchargers, turbos and nitrous.  There are some tricks to running superchargers and turbos though because the factory MAP sensor does not read boost.


In 1988 California 5.0 Mustangs, Ford switched their system of measuring air intake from Speed Density (SD) to Mass Air Flow (MAF) in order to meet the ever increasing emissions standards. In 1989, Ford switched all 5.0 Mustangs to MAF. All 4.6L Mustangs are MAF, as well. The biggest benefit of MAF over SD is how it measures incoming airflow. The older SD system determined engine load and timing/fuel requirements based on manifold vacuum measured by a MAP sensor (Manifold Absolute Pressure). By looking at engine vacuum and RPM, the EEC could figure out how much air was entering the engine and determine what the fuel requirement was for the engine’s operating conditions. This is the main problem with SD for the person who wants to modify their 5.0. Since SD relies on manifold vacuum, when you change anything that modifies engine vacuum (such as camshaft) you can create drivability issues because the EEC gets confused, so to speak.  Furthermore, the factory SD systems are somewhat limited in the horsepower they support because of the Volumetric Efficiency (VE) table that they refer to.  MAF can calculate VE without a VE table. MAF systems can handle vacuum and airflow changes and correctly calculate the needed fuel with basically no idle or drivability problems. There are some issues with MAF systems, but we will look at them later. First let's look at how MAF works.

The MAF is fitted in the air intake system before the throttle body. The MAF sensor is a hollow body where the air entering the engine flows through. Inside the MAF sensor is a small tube with two sensing elements exposed to the incoming airflow.  The smaller tube is a percentage in size compared to the larger tube in the body so the smaller tube can “sample the correct amount of incoming air.  This smaller tube is sometimes called a “sample tube”.  The two sensors consist of very thin platinum wires wrapped around ceramic bobbins. One sensor is used to measure the temperature of the incoming air charge. The other sensor is heated to maintain 200 degrees C above the temperature sensing element. As air flows over the heated element, the element cools. Electronics in the MAF sensor vary the current to the heated element to maintain the 200 degrees C above the temperature sensing element. This change in current is directly related to the mass of air flowing over the sensing elements. The MAF electronics convert this current change into a voltage output reading which is sent to the EEC. Inside the EEC there is a transfer function that converts MAF voltage to an airflow value. By using this table, the EEC can tell how much air is entering the engine at any given time. Also inside the EEC, there is a calibration parameter that refers to the size of the injectors installed in the engine at 39 PSI. Stock 5.0 and 4.6L 2V Mustangs were originally equipped with 19# injectors. The 5.0L / 5.8L and 4.6L 4V Mustang Cobras came with 24# injectors. When relating MAF sensors and injector size, one of the biggest misconceptions about the MAF system is that the MAF is 'calibrated' for a given injector. This is only true with aftermarket MAF sensors, not the stock Ford air meters. What Ford does, is select a MAF sensor and inform the EEC about it by calibrating the airflow Vs voltage transfer function with data obtained from a flow bench. Then they determine how much fuel the engine will require under worst case scenarios, select an injector size, and put that value into the EEC calibration. The MAF sensor and injector size are basically un-related which means a stock 5.0 Mustang's MAF sensor IS NOT calibrated for 19# injectors - the EEC is. Now that the EEC knows what air meter it has and what injectors are being used, it can correctly calculate how much to pulse the injectors to get the desired fuel flow. In simple terms, here is how the EEC figures out how much to pulse the injectors.

When the engine runs, the EEC looks at the air meter voltage and converts this to an airflow value. This airflow value is used to calculate a term called Load. Load is roughly VE and is determined by the ratio of incoming air over how much the engine can hold. If the air meter tells the EEC it is measuring 50 CFM of air and the engine can hold 100 CFM, then 50 / 100 = .5 (Load) or 50% (VE). Actually, the EEC doesn't measure in CFM, since CFM is a VOLUME measurement and the MAF sensor measures the incoming air by MASS. CFM is a bit easier to understand and the result is the same. Now that the EEC has the Load value, it can go to it's fuel lookup tables and get the A/F ratio the engine should be operating at based on Load and RPM. With this number, and by using some math, it figures out how much pulse width to give the injectors based on how much air is entering the engine. Since it knows both airflow and injector size, it's not that difficult a task. The more air, the more fuel is needed which means the injectors need to be pulsed at a larger pulse width. This applies in Open Loop mode only, where the EEC isn't looking at the O2 sensors. During Closed Loop where the EEC IS looking at the O2 sensors, the A/F lookup table is not used. The O2 sensors basically tell the EEC what A/F ratio it needs to run at. Of course there is a lot more to this whole situation as the EEC must also do compensations for things such as engine coolant temp, intake manifold temp, barometric pressure and the accelerator pump, because they all affect how much fuel is needed. We won't go into all of the compensation routines here since it would make things way to complex for the scope of this topic.

Now understanding how the EEC handles fuel, lets look at spark advance. Load is also used in the spark calculations. There are lookup tables that tell the EEC how much timing to run at any given Load and RPM. Again, the EEC looks at the MAF sensor, converts the voltage to an airflow value and ratios that over how much the engine can hold in order to arrive at a Load (VE) value. It then uses this as an input for the spark tables. An engine operating at lighter Loads, or lower VE, requires a lot more spark advance to operate efficiently.

Getting back to the MAF sensor itself, the original 5.0L Mustang air meter is SMALL! Roughly 55mm in diameter and is a restriction in the intake system. 5.0L Cobras and 4.6L 2V Mustangs use a 70mm MAF sensor which is much better and the 5.8L Cobra R and 4.6L 4V Cobra use an 80mm MAF sensor which is rather big and doesn't pose a real restriction until you massively increase the airflow capacity of the engine. As far as MAF sensors go, the 55mm sensor on a 5.0L Mustang should be the first thing to go, as it can limit the amount of power the engine is capable of making. A larger diameter air meter will create less of a pressure drop and be less restrictive. Although you can make lots of power with the stock air meter, it's generally a good idea to swap it out for a larger piece. How much power can you get with the stock MAF? Some have gotten 400+ HP using the stock MAF, but that takes a significant amount of time and effort calibrating the EEC. One example is a car has gone 11.51 @ 118 mph with the stock 55mm MAF sensor and after switching to a larger 80mm Ford air meter and went 11.21 @ 122.

There are various manufacturers of aftermarket MAF sensors, in various sizes, but they all work the same way. They attempt to fool the EEC. All this fooling around can be good, or it can be bad. Surely you've heard about someone installing larger injectors, a ’re-calibrated' MAF sensor, and having drivability problems. Things like surging, poor economy, black smoke coming out of the tailpipes, and part throttle detonation or blown head gaskets from running too lean. These are caused by aftermarket MAF sensors re-calibrated for larger injectors. I'd estimate that 60% of Mustang owners who use these aftermarket MAF meters have one or more drivability problems. Aftermarket MAF sensors calibrated for stock injectors don't really have much of a problem most of the time, but can under certain situations. Let's look at how the aftermarket sensors do their job (or don't do their job) to see why.

When airflow increases, the amount of voltage also increases. If you were to install 30# injectors into a 5.0 Mustang and not re-calibrate the air meter or the EEC, it would run way to rich and pump out lots of black smoke. The reason for this is because the EEC still thinks it has 19lb injectors installed, which flow much less fuel at any given pulse width than the 30lb injectors. So when the EEC goes through its calculations to figure out how much to pulse the injectors, way too much fuel will be injected. Here's the trick the aftermarket MAF people do (not including Kenne Bell which is calibrated in the same fashion as the stock Ford MAF is). Since the EEC looks at the MAF sensor voltage to determine airflow, what if we were to fool the EEC into thinking it had less air coming in, therefore it would calculate a smaller pulse width? That is exactly what a lot of aftermarket companies do. There are a couple different ways to accomplish this. One way is how Pro-M and Ford Motorsport do it. They open up the electronics on the MAF sensor and modify the circuit to lower the output voltage of the MAF sensor. The shape of the voltage airflow curve remains the same (hopefully), but it is shifted down by a ratio of old injector over new injector. This means the output voltage curve of the MAF electronics is scaled by the ratio of the two injectors. Lets say you have 19lbers and switched to 30lbers (19 / 30 = .63). This means the new curve is only 63% of the old curve. Now when the EEC looks at the voltage, it now thinks it's getting less air, and less air means less fuel needed, so it will calculate a smaller pulsewidth which is hopefully close enough to deliver the right amount of fuel. Another method of fooling the EEC is the way C&L/Vortec do it. By changing the ratio of the main bore of the MAF sensor to the sampling tube, you can make the MAF look like it's getting less airflow too. These MAF's use the stock MAF electronics and vary the output voltage curve mechanically. The last way I have seen to fool the EEC is the way Auto Specialties does it. Their method is similar to C&L/Vortec, but they also use a screw positioned in the sampling tube in order to fine tune the bore to sampling tube ratio. By moving the screw in and out, you change the ratio. Each of these methods looks like it should work well, in theory. There is a problem with fooling the EEC in this way and it's called Load. Remember Load is calculated by the ratio of incoming air to how much the engine can hold. Well, now the incoming air information is all wrong so the Load calculation is all wrong also. Since Load is used to determine what A/F ratio and what spark advance to run at any given RPM, you can probably guess that with a re-calibrated air meter you no longer run correct fuel and spark - and you'd be right! As you go up in Load, the amount of spark advance goes down. With the 30lb re-calibrated air meter installed, Load is going to be roughly 35% less than what it actually is. What you end up with is at some RPM / Load points your running more spark advance which is like bumping up the base timing and makes the car a bit quicker. At other RPM / Load points the spark is so over advanced you can get surging, detonation at part throttle or just plain slow down. Let's say the engine is operating at a true .60 Load, but the re-calibrated air meter is tricking the EEC into thinking it's only running at .40 Load (roughly 35% lower than actual). The base spark advance is about 17 degrees over advanced at this point. That's just like setting your base distributor timing at 27 degrees. At Wide Open Throttle on a 93 5.0L Mustang, the over advanced situation goes away since the EEC only uses RPM to figure out spark advance, but the SN-95's use Load all the time.  Let's say we are running 180 degrees engine coolant temp and .70% load on a modified 93 Mustang GT. Normally we would want to run somewhere around a 13.04:1 A/F ratio, but since Load is goofed up we actually run near 14.64:1 which is quite a bit leaner than you'd want to be.  SN95 5.0L are even worse which is why they are evein trickier to get running good.

The larger the injector the MAF is calibrated for, the worse everything gets since the error in the Load calculation gets bigger and bigger. Now these problems don't happen to everyone and hopefully this doesn’t scare, but if you are experiencing derivability problems and you have a re-calibrated MAF, now you know the reason why it runs like it does. Now there is a benefit of having a MAF sensor re-calibrated and it's sort of a side effect of the process. If you run a stock air meter on an engine that can really pull a lot of air, such as those with a supercharger, you can peg the MAF sensor's electronics. Depending on what year Mustang you have, the 'peg' voltage is somewhere around 4.85 or so volts. The EEC will look at this voltage and think there is something wrong. The check engine light will pop on and depending on how your engine is set up, you could blow a head gasket or worse. What happens is the EEC will think the MAF sensor is bad and use a default air charge table to get its airflow values based on throttle position and RPM. Normally this table is calibrated so the engine will run richer than normal which doesn't do any harm. But if you’re pushing lots of boost, it might not be enough fuel. Since the re-calibrated MAF sensor's voltage curve is now lower than the stock one, it takes an awful lot of airflow to peg the meter. That's the good side effect from this type of MAF re-calibration.



Mass Air Flow Sensor Facts
The MAF sensors used on many of today's cars primarily use the two-wire, hot/cold wire, setup to detect the mass of the air passing through it. These wires are designed to give a feedback voltage to the engine control system (EEC, PCM, ECM, whatever) using an electronic function wired into the sensor. Many misconceptions have arisen in the realm of modifying the MAF to gain power on the vehicle. Here are some facts and information to help you better understand the use and function of the system.

The MAF is a sensor. It cannot take an active role in the operation of your vehicle, which is what the PCM does. The PCM uses all of the various inputs and runs the engine according to its program. The MAF transfer function not only tells the computer how much air is coming into the motor, but the function is used to calculate load using other inputs which profiles spark and fuel. As far as sensors go, it is a somewhat complex unit. It basically uses two wires within its body to create a current draw and output based on the different characteristics of the wires. But the way these wires act in the sensor body itself can be somewhat problematic. First, there is the flow of air entering the sensor. The air stream can have many influencing characteristics that can affect the sensor's ability to give accurate output. Turbulence and velocity variations can give false output based on the original flow profile of the sensor. So let's talk about the design for a second. When the engineers at the factory incorporate the sensor into an intake system, they must not assume it to be a perfect flow of air. The air filter, air box, sensor placement and many other factors affect the true sensing capability of the sensor. This is why when a MAF transfer function, the data stored in the computer about the sensor, is derived for one vehicle it may not be identical to the transfer function for a similar vehicle with the same exact sensor. The load calculations will also vary. Likewise, the downstream inputs that can affect the sensor vary from one design to another.

A running engine creates impulses that flow upstream, intake growl noise, that are waves of air that are now impinging on the sensor from behind. In an effort to eliminate the effect of various intake feedbacks the designers use a backflow-preventor in the form of a bar across the MAF sensor cavity using a backing plate to deflect these impulses away from the sensor elements. When the engineers develop the transfer function for a system they measure the flow of the sensor in a real-life situation. Designers actually use a laser Doppler system to precisely measure the flow characteristics. Designing a single basic design that can be used across many applications is the goal so costs can be minimized. Suffice it to say that a MAF from identical cars will not be identical. The variations in the electronics that drive the sensor have some influence on the way the car runs. As a model year progresses other variables, like part lot numbers and such can cause one car to run much better than the next. If all of the variation of the sensors and devices like injectors are taken into account, you could have a marginal car to begin with. This is why some people see great gains with slight mods and others see nothing or it gets worse.

Modifying the MAF has risks as well as potential benefits. Changing the flow characteristics can cause great problems. First, let's look at the post removal issue. Removing the post does increase the flow capacity of the meter, but now has the potential for noise from the intake causing other problems. This is more important at idle and low throttle settings.
Why? The MAF transfer function is not linear. The function is flatter at low flows and increases at an increasing rate as flow increases. If there is airflow noise at the flatter portion of the curve, the noise voltage is a much greater percentage of the total voltage being sent to the computer and the computer may balk. Thus you end up with rough or poor idle. At high flows the noise can be greater but the curve is exponential and the noise is less influential. Also, the velocity of the air in the sensor with no post has dropped at the same load. This affects the load calculation that causes the injector pulses to be off the intended design. They may be better they may be worse. Cars with closed loop operation capabilities can detect the lean or rich condition caused by the change and make adjustments on the fly. Car may start rough but smooth out as you drive. As you drive in the Wide open throttle condition, open loop, the car is now only relying on the data stored in the computer and modifications, which are not "good" or beneficial, will now affect the performance of the motor. The one perceived increase in performance has to do with the fact that the original programming of the PCM is on the rich side, extra fuel for reduced wear and tear on the motor. This modification effectively leans out the mixture and provides more efficient combustion. Over the long run though, the PCM will use it's adaptive capabilities to make the mixture correct as read by the Oxygen sensors. But having changed the flow characteristics of the sensor, the flow across the elements is also changed, possible reduced. Thus the voltage would be lower and the effective flow would cause even leaner conditions. Also, load calculations will probably be off their original curve and injector pulses may be affected. One trick to provide for the change in flow of the no-post MAF is to make a proportional change in the sample tube that contains the sensor wires. Assuming you get the hole size just right, the transfer function of the MAF is still not likely to match that of the original function map in the computer. The curve could be steeper sooner or flatter later or shifted completely.

At a given MAF voltage the air coming into the meter is known through the transfer function table. Knowing that most people drive around in closed loop situations these variations are quenched by other inputs. Just unplug the MAF all together and you will see that it will run however poorly, but it is not dead. The problem with the sample tube issue is that the overall flow characteristics of the MAF are just different than before. If you were to compare the two curves against each other, they will be very close. And it seems for the most part that the increased airflow, especially at WOT, is of greater benefit than the slight miscalibration of the sensor. What has to take place is the voltage should still represent a given flow, the modification just shifts the curve to provide flows at lower throttle levels. Again this can affect load.

Other modifications can affect even a stock sensor. The air box, inlet tube and intake tube to the throttle body will cause the system as a whole to be slightly different. Let's not get too freaked out though. Again, the benefits of these modifications are often marginally good. One key thing to remember is that the closer the MAF is to the throttle body the higher the effect the intake feedback has on the meter's accuracy. The fewer restrictions you have between these parts also can cause problems, usually rough idle and poor performance at low throttle positions. Ideally get the MAF farther away from the throttle body. For the greatest benefit from any modification to the MAF, its flow characteristics must be input into the transfer function table in the PCM. Recalibrating the MAF for larger injectors works somewhat but load calculations will be wrong. Most MAFs are limited by their size as to how much they can flow, but even then you can peg the electronics.
Adding a supercharger can cause the meter to not function to its full potential if flows above the transfer function table range occur. The sample tube size can be adjusted to give a broader range than the .5v to 5.0v the current Ford sensors have. Below are two side by side lists of MAF transfer function for two different setups on the 1994 Mustang GT. The first number in the parenthesis is the voltage and the second is the airflow in KG/hr. Notice that there is a maximum flow of 932 kg/hr on the first and 882 kg/hr on the second. Model year changes or different options in the system caused the difference. Also, the curve for the first one is very similar to the second all the way up to 4.0v and then the first one climbs rapidly.

So even though these are the same model and year, just a MAF swap will cause a discrepancy in the way WOT is computed. This swap is a full swap. The sensor bodies have been very standardized. Swapping just the bodies wouldn't make as much a difference as swapping the electronics. Put the first one in the second car and at the high end the car will get a voltage that represents a flow rate less than the actual flow which is higher, it will run leaner and possibly cause detonation. Now these are just examples and to specifically say what will really happen depends on the other variables. Dirty sensor elements gives less voltage at same flow.
Dirty injectors may cause a lean condition as well as fuel pressure and volume.

U4P0 J4J1
# Mass Air Transfer Function
( 15.9998, 932.145 ) ( 15.9998, 882.085 )
( 5, 932.145 ) ( 5, 882.085 )
( 4.75, 808.577 ) ( 4.6001, 717.327 )
( 4.5, 697.683 ) ( 4.19995, 568.729 )
( 4.25, 598.512 ) ( 3.80005, 443.577 )
( 4, 510.114 ) ( 3.5, 362.466 )
( 3.80005, 446.745 ) ( 3.30005, 313.989 )
( 3.6001, 389.397 ) ( 3.1001, 270.265 )
( 3.3999, 337.118 ) ( 2.8999, 230.66 )
( 3.19995, 290.86 ) ( 2.69995, 195.491 )
( 3, 249.037 ) ( 2.5, 163.173 )
( 2.80005, 211.65 ) ( 2.3999, 148.281 )
( 2.6001, 178.381 ) ( 2.30005, 134.974 )
( 2.3999, 149.232 ) ( 2.19995, 122.301 )
( 2.19995, 123.568 ) ( 2.1001, 110.894 )
( 2.1001, 112.162 ) ( 2, 100.122 )
( 2, 101.389 ) ( 1.8999, 89.9828 )
( 1.8999, 91.2501 ) ( 1.80005, 80.7944 )
( 1.80005, 82.0617 ) ( 1.69995, 72.2397 )
( 1.6001, 65.2692 ) ( 1.6001, 64.3187 )
( 1.5, 57.9818 ) ( 1.5, 57.0313 )
( 1.30005, 44.9914 ) ( 1.3999, 50.3777 )
( 1.19995, 39.2882 ) ( 1.30005, 44.3577 )
( 1, 29.4662 ) ( 1.19995, 38.9714 )
( 0.75, 19.961 ) ( 1, 29.1493 )
( 0.600098, 15.2084 ) ( 0.899902, 25.0304 )
( 0.399902, 10.4557 ) ( 0.800049, 21.2283 )
( 0, 8.87154 ) ( 0.600098, 14.5747 )
( 0.5, 11.7231 )
( 0, 11.7231 )

To modify the MAF sensor is in all practicality a bad move without telling the computer that the flow has increased via the transfer function table. Also, modified intakes will not be as effective as presumed unless the flow changes are calculated also. The best way to increase the flow to the motor and let it know is to get the system tested or get a system that has been flow profiled and includes the ability to program the PCM. You can't just "recalibrate" the MAF. Load will be incorrect. This can effect the durability of the motor especially during WOT driving.



Using an SCT MAF or Lightning MAF With Your Vehicle (Re: LaSota Racing)

One of the real problems you might face when you start making more power with your vehicle is you might just "peg" your mass airflow sensor (MAF). What is pegging? When you peg your MAF, you have not reached the airflow limit of the MAF - MAFs, even smaller sized ones, will flow enormous amounts of air. Pegging refers to hitting the electronic capacity of the sensor.

MAFs use a tiny heated wire in the airflow stream and a thermistor - which is a resistor that varies resistance according to temperature. The ECU keeps scaling voltage up to keep the temperature of the wire the same, but as airflow increases, the wire keeps getting cooler and cooler, and the ECU increases current to keep the temp the same. The current flow is measured and a voltage signal is sent back to the ECU and the ECU uses this to measure the mass or weight of the incoming air. It's a little more complicated than that, but that's basically how it works.

On Ford MAFs, which are manufactured by Hitachi, the MAF will output voltage to battery voltage. However, the ECU is set up to only acknowledge a maximum of about 4.7 volts. This is without a tune. At LaSota Racing we can extend that 4.7 limit to 5.0 volts in your tune to give you a bit more headroom. After the MAF gets past the maximum limit that the ECU can use, bad things start happening.


Bad thing #1 - The ECU controls injector pulse width based on the data it is receiving from the MAF signal. It tries to maintain the commanded air to fuel ratio in the base fuel table. For a naturally aspirated engine at wide open throttle, this is usually around 12.5:1. On a blower or turbo motor, this is 11.5-12.0 depending on a number of variables. Once the voltage limit is attained, the ECU 'thinks' that there is no more air coming into the engine so it does not increase fuel flow. But there is an ever increasing airflow - so what happens is the engine goes lean very quickly. The end result is burned pistons, valves, detonation, blown head gaskets... you get the picture, the bottom line is you better be in a spending mood, because you'll need a new engine. This is especially bad with a blower or turbo motor.


Bad Thing #2 - The MAF does another key function for engine control. It supplies data to the ECU so the ECU can calculate "load". Load is similar to volumetric efficiency, it is a measure of the engine's capacity to fill each cylinder with air/fuel. What's important is that load is used by the ECU for a number of things, two of the things are timing and air to fuel ratio. Generally at low loads, timing is much higher and fuel is much leaner than at higher loads. When the MAF pegs however, the load measurement starts drifting down. So timing goes up and fuel goes even leaner.


Usually on a stock 1989-2004 GT, the MAF is good to around 300 RWHP - some will peg sooner, some later. 80mm Lightning MAFs add a little to that, about 350-375 RWHP, while 90mm Lightning MAFs will peg at about 450 RWHP. SCT BA 2400 MAFs are good to around 625 RWHP and the BA 2800 are good to near 800 RWHP or so. Any of the SCT MAFs will give almost stock drivability, but they need a tune to work properly. Most people skip the 80mm Lightning MAF and go right to the 90mm unit.


Any Ford MAF as well as the SCT MAFs are NOT calibrated for any injector size. The injector size is set in the ECU. We do NOT recommend MAFs that are 'calibrated' to injector size mainly because the calibration is usually not correct and the curve is out of line. These types of MAFs also skew load calculations throwing timing calculations off. We CAN work with these types of MAFs, but drivability will usually never be as good as stock.


Late model cars have the right connector and usually only need a filter adapter, a 4" cone filter and a silicon adapter to adapt the MAF to the powerpipe. Earlier model cars need a pigtail harness. LaSota Racing sells these here. We also sell the filter adapter. We do NOT sell the filters or silicon adapters because there are so many variations. We suggest you contact Summit Racing for the filters - any 4" inlet cone filter that fits should work and conatct Hose Techniques for a silicon adapter.  Late Model cars incorporate the ACT (temp sensor) in the MAF - all SCT MAFs have the temp sensor included. The two outer wires are for the temp sensor and are not used by earlier models using and external sensor.






Air/Fuel Ratios

14.6:1-14.7: is stoich, which is the best burn for ecomomy and emissions. Best power in most cases is between 12.5:1 and 13.5:1 for naturally aspirated engines and around 11.5:1 for forced induction engines.


Fuel Injector and fuel pump information and sizes

Production vehicles with 24 lbs. Injectors
93-95 Mustang Cobra

93-98 Lincoln Mark VIII 4.6L DOHC
95-up Lincoln Continentals 4.6L DOHC
'03 Lincoln Aviator 4.6L DOHC
F-350 with the V10 engine
7.5L 460 V8 trucks
5.4L DOHC Navigator







More EFI Info

Once upon a time an engine needed three things to run: fuel, air, and fire. That’s what carbs, coils, and distributors are for. Modern EFI engines still need these three elements, but they use different hardware to provide them, and a computer to run the whole process.

Today’s electronic engine management systems can process millions of instructions per second to continuously adjust spark and fuel for optimum performance. The computer regulates the electronic fuel-injector pulse width (the time that the fuel injector is open) and ignition lead with input from various sensors. One of the key things the computer needs to know is how much air the engine consumes under a given set of conditions. Three different measurement strategies have evolved to supply the computer with this basic information; in order of sophistication they are: N Alpha, Speed Density, and Mass Flow metering.

N Alpha
A relatively simple design, N Alpha systems use only engine speed and throttle angle to calculate the amount of fuel needed by the engine. This system doesn’t measure airflow directly; instead, engine load is assumed based on throttle-angle versus engine rpm. The various load-rpm points make up the computer’s lookup table, with the amount of fuel needed at each point manually programmed by the tuner. N Alpha systems work well on engines that operate primarily at wide-open throttle—such as race cars—but are much less accurate at part-throttle than more sophisticated systems because of their relatively simple fuel map. They generally do not have a closed-loop mode for air/fuel correction, resulting in part-throttle calibration that is crude at best when compared to other systems. This also makes them incompatible with modern catalytic converters. Any significant engine change requires remapping.

Speed Density
Speed Density systems accept input from sensors that measure engine speed (in rpm) and load (manifold vacuum in kPa), then the computer calculates airflow requirements by referring to a much larger (in comparison to an N Alpha system) preprogrammed lookup table, a map of thousands of values that equates to the engine’s volumetric efficiency (VE) under varying conditions of throttle position and engine speed. Engine rpm is provided via a tach signal, while vacuum is transmitted via an intake manifold-mounted Manifold Air Pressure (MAP) sensor. Since air density changes with air temperature, an intake manifold-mounted sensor is also used.

Production-based Speed Density computers also utilize an oxygen (O2) sensor mounted in the exhaust tract. The computer looks at the air/fuel ratio from the O2 sensor and corrects the fuel delivery for any errors. This helps compensate for wear and tear and production variables. Other sensors on a typical Speed Density system usually include an idle-air control motor to help regulate idle speed, a throttle-position sensor that transmits the percentage of throttle opening, a coolant-temperature sensor, and a knock sensor as a final fail-safe that hears detonation so the computer can retard timing as needed.

GM’s Tuned Port Injection (TPI) set-ups used Speed Density metering from ’90-’92, as did ’91-’93 LT1 engines. All ’86-’87 and ’88 non-California Ford 5.0L-HO engines used Speed Density metering. Most Mopar fuel- injection systems have used Speed Density too.

Because a Speed Density system still has no sensors that directly measure engine airflow, all the fuel mapping points must be preprogrammed, so any significant change to the engine that alters its VE requires reprogramming the computer.

Mass Air Flow
By contrast, Mass Air Flow (MAF) systems use a sensor mounted in front of the throttle body that directly measures the amount of air inducted into the engine. The most common type of mass-flow sensor is the hot wire design: Air flows past a heated wire that’s part of a circuit that measures electrical current. Current flowing through the wire heats it to a temperature that is always held above the inlet air temperature by a fixed amount. Air flowing across the wire draws away some of the heat, so an increase in current flow is required to maintain its fixed temperature. The amount of current needed to heat the wire is proportional to the mass of air flowing across the wire. The mass-air meter also includes a temperature sensor that provides a correction for intake air temperature so the output signal is not affected by it.

The MAF sensor’s circuitry converts the current reading into a voltage signal for the computer, which in turn equates the voltage value to mass flow. Typical MAF systems also use additional sensors similar to those found in Speed Density systems. Once the electronic control module (ECM) knows the amount of air entering the engine, it looks at these other sensors to determine the engine’s current state of operation (idle, acceleration, cruise, deceleration, operating temperature, and so on), then refers to an electronic map to find the appropriate air/fuel ratio and select the fuel-injector pulse width required to match the input signals.

GM used MAF sensors on the turbo Buick V-6 Grand National, ’85-’89 TPI, ’94-’98 LT1, ’96 LT4, and all LS1 engines. Ford has used MAF metering on ’88 California 5.0L engines and all ’89-and-later V-8 engines.

MAF systems are much more flexible in their ability to compensate for engine changes since they actually measure airflow instead of computing it based on preprogrammed assumptions. They are self-compensating for most reasonable upgrades, as well as extremely accurate under low-speed, part-throttle operation. On the other hand, the MAF meter, mounted as it is ahead of the throttle-body, can become an airflow restriction on high-horsepower engines. On nonstock engine retrofits or EFI conversions on engines never produced with fuel injection, it may be hard to package an MAF meter within the confines of the engine bay and available intake manifolding.

Which Is Best?
In a perfect world, virtually all street-performance engines would use Mass Air, due to its superior accuracy and greater tolerance for engine changes. In the past there was a problem on high-horsepower engines because larger-capacity MAF sensors were scarce and prohibitively expensive. Nowadays, oversize MAF sensors are available from Pro-M, Granatelli Racing, and other sources that are compatible with Ford engines and computers. Custom MAF calibration keyed to the specific vehicle, engine, and injector size is also available. With a correctly calibrated oversize meter, reflashing the Ford computer usually isn’t required. (However, before you run out for a larger Ford MAF meter, Fast Track Performance points out that the first limiting factors are the puny Ford 19 lb/hr injectors, which can only support about 320 hp.)

Some oversize MAF meters have also become available for the second-generation (’94-and-later) GM MAF systems, but the selection isn’t as broad as for the Ford guys. The GM MAF engine management computer isn’t as adaptable as Ford’s. Although it will accept larger MAFs, you can’t go up and down more than one injector size with reflashing the computer.

Bigger MAF meters are not readily available for old GM TPI systems, but Granatelli says it is possible to adapt Ford meters to them via a conversion wiring harness. Custom calibration is required, so Granatelli prefers to do the changeover in-house.

For radical engines or engines never produced with fuel injection, an aftermarket user-programmable computer system is usually preferred. Unfortunately, the more-or-less affordable aftermarket systems—including ACCEL/ DFI, Speed-Pro, and Holley—are Speed Density–based and don’t support Mass Air metering. Those systems that do—including Electromotive, Motec, and Pectel units—are more costly, sometimes considerably so. However, Westech Performance reports that it is possible to use Pro-M’s adjustable Optimizer MAF meter and a stock Ford Mustang computer with Ford’s EPEC piggyback programmable unit to run Mass Air on any engine.

If it is not practical to use MAF on your engine due to packaging or hardware constraints, the programmable Speed Density systems are the next best choice because production-based Speed Density systems won’t tolerate major engine changes without computer reprogramming, which usually requires the services of an outside specialist; if the reprogrammer isn’t specifically familiar with your combo, the end results may be less than satisfactory.

On radical engines (those with cam duration over 240 degrees at 0.050 or less than 10 inches of idle vacuum), even user-programmable Speed Density systems have difficulty due to an erratic or insufficient manifold vacuum signal. If the application is for a race car operated primarily under full throttle, N Alpha is the solution. If you intend to drive on the street, a system that blends N Alpha with Speed Density—varying which is in control per specific operating point and conditions—may be the answer. The higher-end aftermarket systems, including Electromotive’s, support this option.

As electronic engine-management system usage becomes more widespread in the car crafting community, prices and ease of use should become more user-friendly. Already, the latest Gen VII ACCEL/DFI system has the ability to construct its own baseline fuel curve, and the new user programming interface is a full-fledged, Windows-compatible program.



Injector Flow Rate (lb/hr) = Engine HP(1) x BSFC(2)
Number of Injectors x Injector duty cycle(3)


Injector Flow Rate (cc/min) = Engine HP(1) x BSFC(2) x 10.5
Number of Injectors x Injector duty cycle(3)


Fuel injectors max HP (lb/hr)* =
Injector flow rate x Number of injectors x 0.8


Fuel injectors max HP (cc/min)* =
Injector flow rate x Number of injectors x 0.8
BSFC x 10.5

Injector flow rate conversions:

Fuel injectors flow (lb/hr)* =
Fuel injector flow (cc/min)


Fuel injector flow (cc/min)* =
Fuel injectors flow (lb/hr) x 10.5


<Ford EEC Trouble Codes>

(O) = Key On Engine Off test (KOEO)
(R) = Key On Engine Running test (KOER)
(M) = Memory code

11 System checks OK -

12 Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too low) - ISC

13 (O) ISC did not respond properly (extends to touch throttle then retracts for KOEO) - ISC
(R) Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle too high)
(M) ISC sticking, open ITS circuit or TP sticking

14 Ignition pickup was erratic - Ignition Systems
E4OD Transmission diesel RPM sensor - Diesel RPM sensor

15 (O) No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test Failure)
(M) KAM (pin 1) was interrupted (was battery disconnected ?)

16 1.9L & 2.5L - Throttle stop set too high - IDLE or Idle Set Procedures
2.3L - RPM's too low - IDLE
(O) Electronic ignition - IDM circuit fault - Ignition Systems

17 1.9L & 2.5L - Throttle stop set too low - IDLE

18 (R) Check base timing & advance function - Timing Tests
(M) Ignition TACH signal erratic - Ignition Systems

19 (O) No Vehicle Power (pins 37 + 57) or bad PCM VPWR Diagnosis
(R) Erratic idle during test (reset throttle & retest) - Idle Set Procedures
Electronic ignition Cylinder ID sensor/circuit problem - Ignition Systems

21 Engine Coolant Temperature (ECT) sensor out of range - ECT

22 MAP (vacuum) or BARO signal out of range - MAP

23 Throttle sensor out of range or throttle set too high - TPS

24 Intake Air Temperature (IAT) or Vane Air Temperature (VAT) sensor out of range - IAT VAT

25 Knock sensor not tested (ignore if not pinging) - KS

26 Mass Air Flow (MAF) or Vane Air Flow (VAF) out of range - MAF VAF
Transmission Oil Temperature (TOT) sensor out of range - Transmissions

27 Vehicle Speed Sensor problem - VSS

28 Vane Air Temperature (VAT) sensor out of range - VAT
2.3L w/Electronic Ignition - Cyl ID, IDM low or right coil pack failure - Ignition Systems

29 Vehicle Speed Sensor problem - VSS


EVP is for vehicles equipped with EGR solenoid(s), with or without an EVP sensor

EVR is for vehicles equipped with an EGR Vacuum Regulator (EVR) and an EGR Valve Position (EVP) sensor

PFE is for vehicles with Pressure Feedback EGR (PFE) sensor and and an EGR Vacuum Regulator (EVR)

If you don't know what type of system you have, go to the EVP heading, which is the first one.
There are pictures under the different headings to help you identify the system.

31 EVP - (O, R, M) EVP signal is/was out of range - EVP
EVR - (O, R, M) EVP signal is/was low - EVR
PFE - (O, R, M) PFE signal is/was low - PFE

32 EVP - (R) EGR not responding properly during test - EVP
EVR - (O, R, M) EVP signal is/was low - EVR
PFE - (R, M) PFE shows low pressure, EGR not seating or memory, not seating intermittently - PFE

33 ALL - (O, M) EGR did not open/ respond during test or if memory code, did not open intermittently - EVP EVR PFE

34 EVP - (R) EGR did not respond properly during test - EVP
EVR - (O, R, M) EVP sensor is/was high - EVR
PFE - (O, R, M) PFE sensor is/was out of range - PFE

35 EVP - (R) Engine RPM's too low to test EGR system - EVP
EVR - (O, R, M) EVP sensor signal is/was high - EVR
PFE - (O, R, M) PFE sensor signal is/was high - PFE

38 Idle Tracking Switch signal was intermittent - ISC

39 Transmission Torque Converter clutch not engaging - Transmissions


41 (R) System lean - Fuel control
(M) System was lean for 15 seconds or more (no HO2S switching) - Fuel control

42 (R) System rich - Fuel control
(M) System was rich for 15 seconds or more (no HO2S switching) - Fuel control

43 (R) HO2S sensor not reading (run at 2000 rpm's for 2 minutes and retest - check for HO2S switching)
(M) Was lean at WOT for 3 seconds or more - Fuel control

44 AIR system inoperative - Air Injection

45 AIR not Diverting (AIRD) - Air Injection
Electronic Ignition - coil primary circuit failure - Ignition Systems

46 AIR Bypass (AIRB) not working - Air Injection
Electronic Ignition - primary circuit failure coil 2 - Ignition Systems

47 Low flow unmetered air (check for small vacuum leaks, injector o'rings, gaskets etc.)
E4OD transmission 4x4 switch/circuit problem - Transmissions

48 High flow unmetered air (check for large vacuum leak, inlet hoses etc.)
Electronic Ignition - coil primary circuit failure - Ignition Systems

49 Electronic Ignition - spout signal circuit problem - Ignition Systems
Transmission 1/2 shift problem - Transmissions

51 Engine Coolant Temperature (ECT) sensor signal is/was too high - ECT

52 Power Steering Pressure Switch/circuit open - PSP
(R) Did you turn wheel during test ?

53 Throttle Position sensor too high - TPS

54 Intake Air Temperature (IAT) or Vane Air Temperature (VAT) signal high - IAT VAT

55 No or low (under 7.5 V) Key Power to PCM pin 5

56 Vane Air Flow (VAF) or Mass Air Flow (MAF) sensor high - VAF MAF
Transmission Oil Temperature sensor too high - Transmissions

57 Intermittent in Park/Neutral/ Switch or Neutral Pressure switch circuit - PNP or Transmissions
1990 Scorpio - Octane jumper installed (information only code - to inform you if it is installed or not)

58 Idle Tracking Switch (ITS) signal problem ISC
Vane Air Temperature (VAT) sensor out of range or open - VAT

59 AXOD 4/3 circuit fault - Transmissions
3.0L SHO - Low speed fuel pump circuit problem - Power / Fuel Pump Circuits
Transmission 2/3 shift problem - Transmissions
1990 Scorpio - Idle jumper installed (information only code - to inform you if it is installed or not)

61 Engine Coolant Temperature (ECT) sensor is or was too low - ECT

62 AXOD (KOEO only) 3/2 circuit short to ground - Transmissions
AXOD (KOEO AND KOER) 4/3 circuit failure - Transmissions
E4OD excessive converter clutch slippage - Transmissions

63 Throttle Position Sensor (TPS) signal too low TPS

64 Intake Air Temperature (IAT) or Vane Air Temperature (VAT) signal low or grounded - IAT VAT

65 Check intermittent HO2S (signal or ground) - Fuel Control
(R) E4OD truck - cycle OD cancel switch after engine ID is received - Transmissions
1984 3.8L ONLY - O, M Battery voltage high (check for electrical system overcharging)

66 Vane Air Flow (VAF) or Mass Air Flow (MAF) signal low - VAF MAF
Transmission Oil Temperature (TOT) signal low (possibly grounded) - Transmissions

67 Park/Neutral circuit fault - PNP
Transmission Manual Lever Position (MLP) sensor circuit - Transmissions
(M) Intermittent Park Neutral Position (PNP) sensor fault - PNP

68 Idle Tracking Switch (ITS) circuit (possibly grounded) - ISC
Vane Air Temperature (VAT) sensor out of range or grounded - VAT
3.8L AXOD -Transmission Temperature Switch (TTS) open - Transmissions
Electronic Transmission - Transmission Oil Temperature (TOT) sensor was overheated - Transmissions

69 AXOD transmission (O) 3/2 switch closed (possible short circuit) - Transmissions
AXOD (M) 3/2 switch open (poss short to power) - Transmissions
E4OD 3/4 shift problem - Transmissions

70 (M) 3.8L AXOD - Data link to instrument cluster fault. Service any other EEC codes, erase memory and retest.
If code is still present refer to instrument cluster diagnosis manual.

71 (M) 1.9L TBI, 2.3L TBI, 2.5L TBI - ITS signal was grounded when throttle should have been opening ITS - ISC
ISC motor problem or Idle Tracking Switch (ITS) signal wire shorted to ground - ISC
(M) 1.9L MFI - PCM re-initialized. Possible electrical noise, case ground or intermittent VPWR problem - VPWR Diagnosis
(M) 3.8L AXOD - Data link to instrument cluster fault - See code 70

72 (R) No MAP or MAF change in "goose" test - retest, check for frequency or voltage change - MAP MAF
(M) 1.9L MFI - VPWR circuit to PCM was intermittent - VPWR Diagnosis
(M) 2.3L T/C - PCM re-initialized. Possible electrical noise, case ground or intermittent VPWR problem - VPWR Diagnosis
(M) 3.8L AXOD - Message center data link circuit fault - See code 70

73 (O) Rerun test, if 73 is still output replace TPS
(R) No Throttle Position Sensor (TPS) change in "goose" test. Must get at least 25% throttle rotation - TPS

74 Was brake depressed after engine ID was received ?
Brake On Off (BOO) signal open or short to ground - BOO

75 Brake On Off (BOO) signal shorted to power - BOO

76 Vane Air Flow (VAF) did not respond to "goose" test - VAF

77 System did not receive "goose" test - see TESTS

78 (M) VPWR circuit to PCM was intermittent or the PCM is bad VPWR Diagnosis

79 A/C is on or pin 10 is shorted to power


81 Boost control solenoid - Solenoids
AIRD solenoid - Solenoids and Air Injection
3.0L SHO - Inlet Air Solenoid - Solenoids

82 2.3L TC - Fan Control wire shorted to ground - A/C and Fan Circuits
AIRB solenoid - Solenoids and Air Injection
3.8L SC - Super Charger Bypass Solenoid - Solenoids

83 High Electro Drive Fan circuit fault - A/C and Fan Circuits
EGR Control solenoid - Solenoids
3.0L SHO - Low Speed Fuel Pump Relay circuit - Power / Fuel Pump Circuits

84 EGR Vacuum Regulator - Solenoids
EGR cutoff solenoid - Solenoids
EGR Vent solenoid - Solenoids

85 2.3L T/C Automatic - 3/4-4/3 Shift solenoid - Transmissions
CANP solenoid (ALL 1989) - Solenoids
(M) 1.9L MFI - System has corrected rich condition - Fuel control

86 2.3L or 2.9L Truck - A4LD 3/4 shift solenoid - Transmissions
(M) 1.9L MFI - System has corrected lean condition - Fuel control

87 (O) Fuel pump circuit fault (check inertia switch) - Power / Fuel Pump Circuits
Vehicles with 2BBL carb - Temperature Compensated Accelerator Pump Solenoid - Solenoids
(M) intermittent in fuel pump primary circuit - Power / Fuel Pump Circuits
NOTE: On some Escorts with automatic seat belts this code is normal IN MEMORY due to the wiring

88 Throttle Kicker Solenoid - Solenoids
Variable Voltage Choke relay circuit fault - VVC
Fan Control circuit fault - A/C and Fan Circuits
A4LD - Converter Clutch Override solenoid - Transmissions
Electronic Ignition - IDM, DPI or spout circuit fault - Ignition Systems

89 A4LD - Converter Clutch Override solenoid - Transmissions
AXOD Torque Converter Control solenoid circuit - Transmissions
Exhaust Heat Control (heat riser) solenoid circuit - Solenoids


91 (R, M) System running lean - Fuel control
Transmission SS 1 circuit/solenoid problem - Transmissions

92 (R) System running rich - Fuel control
Transmission SS 2 circuit/solenoid problem - Transmissions

93 (O) Throttle linkage binding or bad ISC motor ISC (R) HO2S not reading - Fuel control
Transmission TCC circuit/solenoid problem - Transmissions

94 AIR system inoperative - Air Injection
Transmission TCC circuit/solenoid problem - Transmissions

95 (O) Fuel pump: open, bad ground or always on - Power / Fuel Pump Circuits
(R) AIR not Diverting (AIRD) - Air Injection
(M) Possible bad fuel pump ground or open between fuel pump and pin 8 at PCM (Fuel Pump Monitor signal) - Power / Fuel
Pump Circuits

96 (O) Fuel pump monitor circuit shows no power - Power / Fuel Pump Circuits
(R) AIR Bypass (AIRB) not working - Air Injection
(M) (Service 87 code first if present) Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits

97 E4OD OD cancel light circuit failure - Transmissions

98 (R) Did not pass KOEO yet (Get 11 in KOEO first)
Transmission EPC circuit/solenoid failure - Transmissions

99 (R) ISC needs to learn (Let idle for 2 minutes; Erase memory and retest)
Transmission EPC circuit/solenoid failure - Transmissions

111 System checks OK

112 (O,M) Intake Air Temperature (IAT) sensor is/was low or grounded - IAT

113 (O,M) IAT sensor is/was high or open - IAT

114 (O,R) IAT sensor out of range - IAT

116 (O,R) Engine Coolant (ECT) sensor out of range - ECT

117 (O,M) ECT sensor is/was low or grounded - ECT

118 (O,M) ECT sensor is/was high or open - ECT

121 (O,R,M) Throttle Position (TP) sensor out of range - TPS

122 (O,M) TP low (possibly grounded or open circuit) - TPS

123 (O,M) TP is/was high or short to power - TPS

124 (M) TP voltage was higher than expected - Fuel control

125 (M) TP voltage was lower than expected - Fuel control

126 (O,R,M) MAP or BARO sensor out of range - ">MAP

128 (M) MAP vacuum has not been changing - check vacuum lines - ">MAP

129 (R) No MAP or Mass Air Flow sensor change during "goose" test - MAP MAF

136 (R) Oxygen sensor not switching/system lean Left or Front HO2S - Fuel control

137 (R) Oxygen sensor not switching/system rich Left or Front HO2S - Fuel control

138 (R) Fault in Cold Start Injector circuit - Fuel control

139 (M) Oxygen sensor not switching Left or Front HO2S - Fuel control

144 (M) Oxygen sensor not switching Single, Right or Rear HO2S - Fuel control

157 (R,M) Mass Air Flow signal is/was low or grounded - MAF

158 (O,R,M) MAF sensor is/was high or short to power - MAF

159 (O,R) MAF sensor is/was out of range - MAF

167 (R) No Throttle Position sensor change in "goose" test (must get at least 25% rotation) - TPS

171 (M) Oxygen sensor not switching - system was at adaptive limits - Single, Right or Rear HO2S - Fuel control

172 (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S - Fuel control

173 (R,M) Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S - Fuel control

174 (M) Oxygen sensor was slow in switching Single, Right or Rear HO2S - Fuel control

175 (M) Oxygen sensor not switching - system was at adaptive limits - Left or Front HO2S - Fuel control

176 (M) Oxygen sensor not switching - system is or was lean Left or Front HO2S - Fuel control

177 (M) Oxygen sensor not switching - system was rich Left or Front HO2S - Fuel control

178 (M) Oxygen sensor was slow in switching Left or Front HO2S - Fuel control

179 (M) Fuel system was rich at part throttle Single, Right or Rear HO2S - Fuel control

181 (M) Fuel system was lean at part throttle Single, Right or Rear HO2S - Fuel control

182 (M) Fuel system was rich at idle Single, Right or Rear HO2S - Fuel control

183 (M) Fuel system was lean at idle Single, Right or Rear HO2S - Fuel control

184 (M) Mass Air (MAF) output higher than expected - Fuel control

185 (M) Mass Air (MAF) output lower than expected - Fuel control

186 (M) Injector pulse width longer than expected or Mass Air Flow (MAF) lower than expected - Fuel control

187 Injector pulse width shorter than expected or Mass Air Flow (MAF) higher than expected - Fuel control

188 (M) Fuel system was rich at part throttle - Left or Front HO2S - Fuel control

189 (M) Fuel system was lean at part throttle - Left or Front HO2S - Fuel control

191 (M) Fuel system was rich at idle - Left or Front HO2S - Fuel control

192 (M) Fuel system was lean at idle - Left or Front HO2S - Fuel control

193 Failure in Flexible Fuel (FF) sensor circuit - Fuel control

194 (M) Perform cylinder balance test to check for inoperative injectors

195 (M) Perform cylinder balance test to check for inoperative injectors

211 (M) Ignition PIP signal was erratic or missing - Ignition Systems

212 (M) Ignition TACH signal was erratic (module/wiring) or SPOUT circuit fault - Ignition Systems

213 (R) Ignition SPOUT or SAW circuit open or shorted - Ignition Systems

214 (M) Error in Cylinder ID (CID) circuit or signal - Ignition Systems

215 (M) Primary circuit failure - ignition coil 1 - Ignition Systems

216 (M) Primary circuit failure - ignition coil 2 - Ignition Systems

217 (M) Primary circuit failure - ignition coil 3 - Ignition Systems

218 (M) IDM signal open or high or left coil pack failure - Ignition Systems

219 (M) SPOUT circuit failure, timing defaulted to 10 degrees - follow code 213 diagnosis

222 (M) IDM open or high or right coil pack failure - Ignition Systems

223 (M) Dual Plug (DPI), SPOUT or IDM circuit fault - Ignition Systems

224 (M) Failure in ignition coil primary circuit - Ignition Systems

225 (R) Knock sensor not tested (ignore if not pinging) - KS

226 (O) Ignition Diagnostic Monitor (IDM) signal fault - Ignition Systems

232 (M) EI primary coil circuit failure - Ignition Systems

238 (M) EI primary circuit failure - ignition coil 4 - Ignition Systems

311 (R) AIR system not working - Single, Right or Rear HO2S - Air Injection

312 (R) AIR not diverting - Air Injection

313 (R) AIR not bypassing - Air Injection

314 (R) AIR inoperative, Left or Front HO2S - Air Injection

326 (R,M) Pressure Feedback EGR shows low pressure EGR not seating or not seating intermittantly - PFE

327 (O,R,M) EGR feedback signal is/was low - EVR or PFE

328 (O,R,M) EGR Valve Position (EVP) is/was low - EVR

332 (R,M) EGR did not open/respond during test or if memory code, did not open intermittantly - EVR or PFE

334 (O,R,M) EVP sensor is/was high - EVR

335 (O) EGR feedback signal is/was out of range - EVR or PFE

336 (O,R,M) PFE sensor signal is/was was high - ">PFE

337 (O,R,M) EGR feedback signal is/was was high - EVR

338 (M) Cooling system did not heat up (check cooling system / thermostat operation)

339 (M) Cooling system overheated (check cooling system / thermostat operation)

341 (O) Octane jumper installed (information only code to notify you if it is installed)

411 (R) Idle speed system not controlling idle properly (generally idle too high) - ISC

412 (R) Idle speed system not controlling idle properly (generally idle too low) - ISC

452 (M) Vehicle Speed Sensor (VSS) problem

511 (O) No power to PCM pin 1 or bad PCM (processor)

512 (M) Memory power (PCM pin 1) was interrupted - Was battery disconnected ?

513 (O) Replace processor (PCM) (internal failure)

519 (O) PSP switch/circuit open - PSP

521 (R) Wheel not turned during test or PSP problem - PSP

522 (O) Park/Neutral Position (PNP) or Clutch Pedal Position (CPP) circuit fault - PNP
Transmission MLP sensor out of range in park - Transmissions

524 Problem in low speed fuel pump circuit - Power / Fuel Pump Circuits

525 (O,M) Park/Neutral Position (PNP) or Clutch Pedal Position (CPP) circuit fault - PNP

528 (M) System shows voltage at pin 10 (is A/C on ?) or pin 30 (PNP, CPP switch) - PNP

529 (M) Data Communications Link to processor failure
Service any EEC codes, erase memory and retest. If code is still present refer to instrument cluster diagnosis manual.

533 (M) Data Communications Link to instrument cluster failure - see 529

536 (O,R,M) Brake On Off open or shorted to ground - BOO

538 (R) System did not receive "goose" test - TESTS

539 (O) System shows voltage at PCM pin 10. Is A/C on ?

542 (O,M) Fuel pump open, bad ground or always on - - Power / Fuel Pump Circuits

543 (O) Fuel pump monitor circuit shows no power - Power / Fuel Pump Circuits
(M) (Service 556 code first if present) Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits

551 Problem in Intake Manifold Runner Control (IMRC) solenoid/circuit - Solenoids

552 (O) AIRB solenoid/circuit failure - Solenoids

553 (O) AIRD solenoid/circuit failure - Solenoids

554 (O) Fuel Press Regulator Control solenoid/circuit fault - Power / Fuel Pump Circuits

556 (O,M) Fuel pump relay primary circuit fault - Power / Fuel Pump Circuits

557 (O,M) Low speed pump relay primary circuit fault - Power / Fuel Pump Circuits

558 (O) EGR vacuum regulator solenoid/circuit failure - EVR or PFE or Solenoids

559 (O) A/C relay primary circuit fault - A/C and Fan Circuits

563 (O) High Fan Control (HFC) circuit failure - A/C and Fan Circuits

564 (O) Fan Control (FC) circuit failure - A/C and Fan Circuits

565 (O) Canister Purge 1 solenoid/circuit failure - Solenoids

566 (O) transmission 3/4 shift solenoid/circuit - Transmissions

569 (O) Canister Purge 2 solenoid/circuit failure - Solenoids

578 (M) A/C pressure sensor VREF short to ground - A/C and Fan Circuits

579 (M) ACP sensor did not change with A/C on - A/C and Fan Circuits

581 (M) Cooling fan current was excessive - A/C and Fan Circuits

582 (O) Open cooling fan circuit - A/C and Fan Circuits

583 (M) Fuel pump current was excessive - Power / Fuel Pump Circuits

584 (M) Open power ground circuit - Power / Fuel Pump Circuits

585 (M) A/C clutch current was excessive - A/C and Fan Circuits

586 (M) Open circuit in A/C clutch - A/C and Fan Circuits

587 (O, M) Communication problem between PCM and Variable Control Relay Module (VCRM) - Power / Fuel Pump

617 (M) Transmission shift failure (1/2 shift) - Transmissions

618 (M) Transmission shift failure (2/3 shift) - Transmissions

619 (M) Transmission shift failure (3/4 shift) - Transmissions

621 (O) Solenoid/circuit failure - shift solenoid 1 - Transmissions

622 (O) Solenoid/circuit failure - shift solenoid 2 - Transmissions

624 (O,M) Solenoid/circuit failure -Electronic Pressure Control (EPC) current is high - Transmissions

625 (O,M) Solenoid/circuit failure - Electronic Pressure Control (EPC) current is low - Transmissions

626 (O) Transmission Coast Clutch (CCS) Solenoid/circuit fault - Transmissions

627 (O) Torque Converter Clutch circuit fault - Transmissions

628 (M) Excessive converter clutch slippage - Transmissions

629 (O,M) Torque Converter Clutch circuit fault - Transmissions

631 (O) Overdrive Cancel Light circuit problem - Transmissions

632 (R) E4OD - Transmission Control Switch (TCS) should be cycled once between engine ID and Goose test

633 (O) 4x4L switch should be in 4x2 or 4x4 high for the test

634 (O,M) Park/Neutral Position (PNP) or Clutch Pedal Position (CPP) circuit fault
Electronic shift transmission - Manual Lever Position (MLP) sensor out of range in PARK - Transmissions

636 (O,R) Transmission Oil Temperature (TOT) sensor out of range - Transmissions

637 (O,M) TOT sensor is/was high or open - Transmissions

638 (O,M) TOT sensor is/was low or grounded - Transmissions

639 (R,M) Transmission Speed sensor (TSS) circuit fault - Transmissions

641 (O) Transmission solenoid/circuit failure Shift Solenoid 3 - Transmissions

643 (O)(M) Torque Converter Clutch (TCC) circuit - Transmissions

645 (M) Transmission 1st gear failure - Transmissions

646 (M) Transmission 2nd gear failure - Transmissions

647 (M) Transmission 3rd gear failure - Transmissions

648 (M) Transmission 4th gear failure - Transmissions

649 (M) Transmission EPC system failure - Transmissions

651 (M) Transmission EPC solenoid/circuit fault - Transmissions

652 (O) Torque Converter Clutch (TCC) circuit fault - Transmissions

654 (O) Transmission selector not in PARK - Transmissions

656 (M) Torque Converter Clutch (TCC) slip - Transmissions

657 (M) Transmission temperature was excessive - Transmissions

998 (R) Did not pass Key On Engine Off test yet (Get 111 in KOEO first)
(O) Transmission Electronic Pressure Control (EPC) solenoid/circuit fault - Transmissions


ACT = Air Charge Temperature Sensor
BP = See MAP
EEC = Electronic Engine Control System
ECT = Engine Coolant Temperature Sensor
EGR = Exhaust Gas Recirculation Valve
EVP = EGR Valve Position Sensor
HEGO = Heated Exhaust Gas Oxygen Sensor
KOEO = Key On Engine Off
KOER = Key On Engine Running
MAF = Mass Air Flow Sensor
MAP = Manifold Absolute Pressure Sensor
MLP = Manual Lever Position
PCM = Powertrain Control Module
SPOUT = Distributor Jumper to Allow Initial Timing
TP = Throttle Position Sensor