ECU problems

mykscholze said:

Well we took the car to the shop to get gears installed and have them troubleshoot the the cause of the Check Engine Light.

My mechanic said that there are hard codes in the computer that he can't reset and most likely the computer needs to be replaced.

Is this common and about how much will replacing the A9L cost?

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honestly, that sounds like some BS. do you know what codes you have? assuming its an 87-95 you can check codes yourself, its free and very simple. CHECK THIS THREAD . let us know what codes you get and we'll help you fix it.

I think you'll get better results by replacing your mechanic.

^^^
LOL

Find out what the codes are and work through them yourself.

The is a link in my sig that will walk you through pulling the codes if you don't have a scanner.

Once you have the codes, you can find plenty of info here to correct the problem.

What is this person's definition of a Hard code? Andy, Jason and Tengram have provided some excellent advice. There are but a couple codes that I can think of which *might* be solved with a new puter.

Good luck.

mykscholze said:

The codes I got from the shop are:

34 - EVP or PFE voltage above closed limit during operation.
Thermactor tube to back of heads and bypass valves have been removed, not sure if they are part of the problem here or not. Earlier we were also getting code 84, I replaced the vaccume regulator and that code went away.

66 - MAF (2.3 Turbo, VAF) below minimum test voltage.
Have a new MAF sensor, granitelli calibrated for 24lb. injectors and BBK Cold air intake. MAF is not calibrated for cold air intake could this be the problem?

67 - Clutch switch open, AC left on, transmission in gear.
?

96 - FP circuit failure, battery to processor.
?

Idle is surging bad, occasionally feels like it is missing and smells fat.

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34 - egr not closed when its supposed to be...might want to take it off and clean it, carbon buildup will cause this. otherwise you may need a new egr sensor. could be causing some of your driveability quirks.

66 - MAF below test voltage...this is a real problem and will cause driveability problems. try these test:


67 - gear switch is probably faulty or wiring not hooked up. shouldn't cause much trouble though...possible idle issues though i've never had any (my switch is faulty)

96 - fuel pump secondary circuit failure...could simply be a faulty relay or open wiring going to the relay. you could check the wire going to pin 19 at the ECM with engine running for 12vdc...if present than it could actually be an ECM problem. my suggestion though, reset codes and see if this one comes back. i've gotten it from time to time and have had no problems because of it.

actually it would be a good idea to reset codes(by disconnecting the battery for 15 minutes) and see what codes return. also run the self-test and follow the KOER test with a quick tap of the throttle to initiate the cylinder balance test. this will tell you if you have a compression issue, bad spark, or a stuck fuel injector on one cylinder...and it'll tell you which cylinder. let us know

BTW, that yellow text was nearly impossible for me to read. probably have better luck getting responses with a different color. my2cents

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1.5 ohm.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.

This will affect idle quality by diluting the intake air charge

Code 66 MAF below minimum test voltage.
Insufficient or no voltage from MAF. Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for computer power relay switched +12 volts. Check for 12 volts between the red and black wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF. This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater heats the MAF sensor element causing the resistance to increase. The amplifier buffers the MAF output signal and has a resistor that is laser trimmed to provide an output range compatible with the computer's load tables.

The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element, remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable brake parts cleaner (same stuff in a bigger can and cheaper too).

The MAF output varies with RPM which causes the airflow to increase or decease. The increase of air across the MAF sensor element causes it to cool, allowing more voltage to pass and telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins 50 & 9 on the computer.

At idle = approximately .6 volt
20 MPH = approximately 1.10 volt
40 MPH = approximately 1.70 volt
60 MPH = approximately 2.10 volt

Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the computer (tan/light blue wire) should be less than 2 ohms.

There should be a minimum of 10K ohms between either pin C or D on the MAF and ground.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Try cocking the MAF (rotating the MAF housing) if everything checks out good. Some CAI kits cause turbulence in the airflow that upsets the MAF sensor readings.

mykscholze said:

Am I correct in saying that the MAF for a 1993 Cobra is 70mm and calibrated for 24lb injectors? Would this work with the cold air intake?

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The CAI shouldn't make a HUGE difference, but every car seems to be a little different.

Ford calibrated all of its MAF meters to the computer, not to a particular injector size.
There are separate settings in the computer for the injector size.

While running 24Lb injectors the options for MAF meters are limited to...
An aftermarket MAF (which will be calibrated for your injector/computer combo)

OR

Convert to 93 Cobra computer (X3Z), MAF, and MAS (the little black sensor on the MAF tube).
There aren't any performance gains to be realized by converting to the Cobra setup, but you would retain stock type drivability.


jason

mykscholze said:

Well I replaced the EGR position sensor, and tested the EGR valve (we just put some alcohol on the pintle valve to see if it leaked) and both of them seem to be working but the codes still came up and it is still surging and running rich.

Vacuum at idle is as low a 5" and we think that we might have a vacuum leak at the manifold... (part of the reason we think this is we pumped vacuum to the EGR and there was no change in the idle)

Would this cause the computer to read errors in the EGR and MAF if unmetered air was getting into the air stream?

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It will not affect the MAF codes.


The 5" of vacuum is definitely not good. It might have some influence on the EGR problem.