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Thread: No Start

  1. #1
    Randy in NM
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    No Start

    Hi all,

    I have an 88 535is that will not start. I put the key in the on position with dash lights but the fuel pumps do not run. I've replaced both the main and fuel pump relays. The fuel pumps run when relay is jumped and main pump shows 3.x amps when tested, below bently specs. Should I expect the fuel pumps to run with the key in the on position without an attempt to start? Also, reference sensor shows 1018 ohms resistance between 1 & 2 but nothing between 2 & 3 and 1 & 3 with my ohmeter set to 200k. Any ideas?

    Thanks in advance,
    Randy


  2. #2
    KevinD
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    Re: No Start

    Fuel pumps start working when the engine starts to crank over...not when the key is only in the on position.

    Your reference sensor ohms are fine...960-1050 range. For maintenance purposes, change the sensors every 80-100k miles.

    Please explain "will not start:
    1/ Crank-no start?
    or
    2/ Nothing?

  3. #3
    Randy in NM
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    Re: No Start

    Thanks for the reply. Car cranks strong and actually ran again after installing the new relays. Then died after about two blocks of driving, wouldn't start, then started again hours later and the next morning. I'll check for spark next.

  4. #4
    Randy in NM
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    Re: No Start

    I pulled a spark plug and grounded it to the valve cover to test for spark and there was none. I am stumped and any help would be great.
    Randy

  5. #5
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    Re: No Start

    It still could be your flywheel sensors. They can test good by resistance and still be faulty. I had one go in my old white car. I shut it off at a gas station and it wouldn't restart. With the key in the run position it was ready to run, but it just didn't know the engine was cranking. Another thing to check is the idle control valve. It should buzz very slightly with the ignition on. That tells you the ecu is powered up and the relays are good.

    I might have a set of sensors at my house, either the ones from your old 533 or the ones from one of my old 528's. I'll check when I get home if I remember. Swapping them out with a known good set is the only way to really eliminate them as a possibility.

    Other than that it can be a bad OBC anti-theft relay. I've never had one fail, but its not unheard of. The flywheel sensors fail much more frequently.1988 528e- 299rwhp/360rwtq
    1983 528e- stock 2.7e motor, 4hp22 from an '86
    1985 528e - RIP
    1984 533i - RIP

  6. #6
    Randy in NM
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    Re: No Start

    Still no spark, no running fuel pumps (only when jumped). I am beginning to suspect the Motronic control unit. Anybody in Albuquerque have one? Last three numbers are 059. I have yet to test the sensors with alternates but ohms look good.

    Randy

  7. #7
    butlertron
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    Re: No Start

    The pumps wont run unless the speed and reference sensors are good. If the engine is stopped or the ecu doesn't know its running, it wont run the fuel pumps.

    Can you solder? The -059 has a few notorious solder joints. I doubt this is the issue, but it could be. If you're handy with a soldering iron you can pop the cover off and reflow some of the joints. That could do it.

  8. #8
    Randy in NM
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    Fixed!

    It was the classic 059 Motronic ECU cracked solder joint to the power transistor that controls spark to the coil. Reflowed and reinstalled...started right up. Thanks to butlertron for the test sensors and encouragement.

    Randy

    http://www.e38.org/e28/louielouie/dme_fix.html

  9. #9
    butlertron
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    Re: Fixed!

    Great news!

    I should have suggested that you check for 12 volts at the 15+ terminal on the coil with the key in the "run" position. That would have been a big red flag, but I didn't even think of it. At least it worked out though.

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