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Thread: 1985 E23 745i ECU/DME repair?

  1. #1
    Join Date
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    Exclamation 1985 E23 745i ECU/DME repair?

    IMG_7866.jpg
    In desperate search of a complete replacement ECU for my new to me '85 745i, or information on how to repair my original DME.

    The original ECU in my car will not fire the coil or injectors, despite verifying the function of the wire harness itself, fuses, main DME relay, ignition coil, ignition switch, battery grounds and 12v leads, crank position sensors, and the double checking the timing tab on the torque converter.

    When I first began testing the engine electronics, I installed an injector noid test light on one of the fuel injector wire connectors, and I also installed a calibrated spark tester on the main ignition coil lead.
    Upon turning the key on, and without cranking the engine, the injector noid light lit up continuously without pulsing, and the ignition coil fired for less than a second, and did not fire again.
    Despite the engine cranking, +12v DC to both sides of coil, and properly functioning crank position sensors, there was no signs of life, no pulse from the noid light, and no further spark from the coil.
    Repeated attempts to start the car made no difference, and eventually the injector noid light stopped illuminating completely, and the coil ceased to fire on any other key off/key on attempts.

    Any advice would be greatly appreciated, I'll even entertain aftermarket ECU solutions if anyone is aware of one!


    BMW part #12 14 1 286 050
    Bosch part #0 261 200 013
    Last edited by E30 FTW; 12-30-2017 at 04:11 AM.

    •2000 X5 4.4i •1991 325i •1991 318iS •1984 318i •1985 745i •1988 635CSi •1972 2002 •1972 Datsun 510 Wagon •1978 Datsun 280z SCCA racecar •1978 Mercedes-Benz 450SEL •1978 Silver Streak Continental •1963 Jeep Gladiator J300 •1994 Ford Ranger

  2. #2
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    I don't know if this will help but Alan hardy of h & b BMW in Berkeley ca imported those cars back in the day along with 323's, m6's, m1's

  3. #3
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    Can you open up the casing so we can see clear pictures of the board? May be tough to find board level replacement parts for something this old
    Buy my native installed ISIS ISTA-D/ISTA-P bmw diagnostic laptop. More Info Here!

  4. #4
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    Quote Originally Posted by Driiven View Post
    Can you open up the casing so we can see clear pictures of the board? May be tough to find board level replacement parts for something this old
    Sure thing.

    I opened the case up after attempting to start the car the first time to see if I could locate any issues.
    I found the typical cracked solder joints on the large driver transistors and went ahead and re-flowed those joints and any other suspect areas.
    I also found a badly burned trace on the board, so I cleaned up the carnage the best that I could, and added a jumper wire in an attempt to bypass the damaged portion of the trace...
    Reinstalled the DME into the car after my "repairs", and there was zero change/improvement; upon turning the key on (ignition on) the injector noid test light stayed on constantly without pulsing, and the coil briefly fired. After multiple attempts of turning the key on and off for testing, the noid light stayed off and the coil failed to trigger again. No fuel pump trigger either.

    Another weird issue/symptom I forgot to mention was the behavior of the transmission fault light; before I opened the DME up and reflowed the solder joints/repaired the burned trace, the transmission fault light would come on when the key was turned on, but would extinguish when I tried to crank the engine. After I opened the DME and then reinstalled it, the transmission fault light no longer lit up when the key was turned on, but oddly enough disconnecting one or the other of the large DME harness connectors would cause the transmission fault lamp to light up (while the ignition is on)...

    IMG_7850.jpg

    - - - Updated - - -

    IMG_7861.jpg

    •2000 X5 4.4i •1991 325i •1991 318iS •1984 318i •1985 745i •1988 635CSi •1972 2002 •1972 Datsun 510 Wagon •1978 Datsun 280z SCCA racecar •1978 Mercedes-Benz 450SEL •1978 Silver Streak Continental •1963 Jeep Gladiator J300 •1994 Ford Ranger

  5. #5
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    Sounds like either the drive transistor has failed or the circuit it trying to drive has a short or faulty component attached(if you had it plugged into the loom when you tried to power it up). try measuring the ohms of the injectors/wiring and coil. You should be able to source a replacement transistor if it has failed.
    Last edited by Omega man 1969; 12-30-2017 at 07:59 AM.

  6. #6
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    The DME provides a ground to an injector when the injector is supposed to “fire.” I’m betting the DME is toast as the burned “trace” means that excessive current flowed through the trace. That means whatever is at the “drain” side of the trace is likely shorted, and therefore bad.

  7. #7
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    Quote Originally Posted by Omega man 1969 View Post
    Sounds like either the drive transistor has failed or the circuit it trying to drive has a short or faulty component attached(if you had it plugged into the loom when you tried to power it up). try measuring the ohms of the injectors/wiring and coil. You should be able to source a replacement transistor if it has failed.
    Good call sir, that's the conclusion I think I'm headed too.

    I will take a little extra time and ohm out the injectors, coil, and wiring.

    - - - Updated - - -

    Quote Originally Posted by MarcoZandrini View Post
    The DME provides a ground to an injector when the injector is supposed to “fire.” I’m betting the DME is toast as the burned “trace” means that excessive current flowed through the trace. That means whatever is at the “drain” side of the trace is likely shorted, and therefore bad.
    Omega man 1969 is thinking the same thing, good call.

    •2000 X5 4.4i •1991 325i •1991 318iS •1984 318i •1985 745i •1988 635CSi •1972 2002 •1972 Datsun 510 Wagon •1978 Datsun 280z SCCA racecar •1978 Mercedes-Benz 450SEL •1978 Silver Streak Continental •1963 Jeep Gladiator J300 •1994 Ford Ranger

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