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Thread: Start circuit not working properly after engine swap

  1. #1
    Join Date
    Jan 2012
    Location
    Victoria, B.C. Canada
    Posts
    82
    My Cars
    1988 BMW 635csi

    Start circuit not working properly after engine swap

    I just replaced my half million km m20b27 with another 100,000km m20b27. I used the old wiring harness and after a fresh rebuild, the new engine plopped right in.

    All grounds are connected, starter motor is good, battery shows 13volts, main relay works.

    When I go to start, the cold start valve actuates/clicks and the main relay clicks and there is powrr across all components of the start circuit but that's all. The starter and it's relay both work and we're tested with multimeters as well as with a battery for functionality. I made sure this wasn't the issue 100 times over. For some reason, I can't get power to the starter. There's power to the whole start circuit otherwise. And yes it is wired correctly

    I'm thinking there must be a interruption in the power line to the relay on the starter motor?

    Any other ideas?

  2. #2
    Join Date
    Oct 2015
    Location
    Illinois
    Posts
    120
    My Cars
    740 735 635 535 318is
    Check for Batt+ at the starter on the large connection, and Batt+ on the starter solenoid when the ignition key is turned to start. Load test the engine ground, or hook a heavy gage (jump starting cable) between Batt - and the metal case of the starter. One of these has to be bad, or the starter itself does not work.

    Sent from my SM-G900V using Tapatalk

  3. #3
    Join Date
    Jan 2012
    Location
    Victoria, B.C. Canada
    Posts
    82
    My Cars
    1988 BMW 635csi
    So the wire going to the starter solenoid was getting power but the wire was eroded and broken between the ECU and power supply so it wasn't getting the message to do its thing. Now I have other problems but I'll start a separate thread

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