ECU Question Please help

Posted by DJ23GSX, Nov 1, 2006
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  1. DJ23GSX

    DJ23GSX Proven Member

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    Right now my ecu (90 gsx) has a leaky cap and shuts off once in a while so i purchased another 90 Ecu that has been rebuilt. After swapping them out i noticed that the new rebuilt ecu idles at 1200rpms and reads 52hz airflow according to my datalogger. I can only manage to get the idle down to around 900 if i lean out the afc 17% but my airflow reading is still around 45hz. My leaky cap ecu idles fine and only reads 27hz at idle. I also noticed that with the rebuilt ecu the iac doesn't move from 0 but with the leaky one it goes up and down just like its supposed to.

    My first question is this rebuilt ecu junk? or is it maybe a 91-92 ecu?
    What if its a 91-92 ecu and i didn't switch pins 6 and 14 would the car even run?

    The part number on my leaky ecu is MD145903
    and the rebuilt one is MD128625. I understand the rebuilt one is a fwd but does that make a difference?

    Is there any way i could tell if the shop that rebuilt this ecu used a different year circuit board than the part number states on the case?

    Any help would be great.
    Thanks
     
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  2. JayRolla

    JayRolla Proven Member

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    Have you put the old one back in just to make sure it fix's the problem. Also I know ive used a 90 ecu in my 91 and it worked fine, just the speedo was wierd.
     
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  3. DJ23GSX

    DJ23GSX Proven Member

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    Yes the old leaky one is back in and it idles fine and the iac is working again according to the datalogger
     
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  4. JayRolla

    JayRolla Proven Member

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    Hmmm, do you have any buddys that will let you use there ECU? Just to try another one.
     
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  5. DJ23GSX

    DJ23GSX Proven Member

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    No one with a 90 ecu.
     
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  6. steve

    steve DSM Wiseman

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    MD145903 90 Federal Turbo MT AWD ECU
    MD128625 90 Federal Turbo MT FWD ECU

    If the ECU actually matched the case the four digit number on the edge connector will match the last 4 digits of the E2T number on the label on the top case.
    For example the MD128625 is E2T34474 and the connector should say 4474.

    A correctly working ISC will start out at around 120 steps when the ignition is first turned on and than after the engine fires it will drop to 0 steps until the FIAV begins closing. Then depending the the ECT and RPMs the ISC will work it's way up to 13 to 20 steps at idle on a warmed up car and stay pretty stable, not jump around, not max out in either direction.

    The quality of final testing, including the ISC operation, ranges all over the map on rebuilds. One test is to check how the car idles up when you turn on the AC and idles down when you turn it off after a ECU reset.

    Steve
     
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  7. DJ23GSX

    DJ23GSX Proven Member

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    The rebuilt ecu doesn't do anything at all with the iac. It sits at 0 the whole time. It idles at 1200rpm and doesn't move no matter what i turn on for accesories. Like i said before the only way i can get the idle down is to lean the afc 15% and even then it still idles around 900 and almost stalls when i touch the gas. My leaky ecu does exactly what its supposed to it starts at 120 then goes right down and settles around 25 at idle. When i turn on the a/c the iac goes up and keeps the idle at 750. The numbers on the connector match so i guess its the correct board.
     
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  8. DJ23GSX

    DJ23GSX Proven Member

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    I spoke to the seller of this ecu and he claims he is a mechanic and keeps telling me that the ecu is fine and its the car that is rejecting the ecu.

    Is there any truth to this at all?
     
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  9. steve

    steve DSM Wiseman

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    No. How does a car reject an ECU? It's not like an organ transplant.


    For testing purposes you can either put the 90 ECU in a friends 91+ Car or put a 91+ ECU in your car by swapping pin 6 and 14 on the harness. That takes all of a minute with a jewelers screwdriver to release the pin and switch them.

    Off hand I'm guessing that the "new" ECU has problems with it's ISC drivers and can't move the pintle in to lower the RPM at idle.

    Steve
     
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  10. TSisleeper

    TSisleeper Proven Member

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    I have a MD145903 eprom ecu that I'm selling, not that it helps your situation, good luck though man
     
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  11. DJ23GSX

    DJ23GSX Proven Member

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    That what i thought and i bet his claims of being a mechanic are total B.S. too. I will try and get my hands on another ecu to test.

    Thanks
     
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