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Thread: Car stalls when LM touches chassis

  1. #1
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    Car stalls when LM touches chassis

    Hi guys,
    Hope you are all well. Strange issue - I have an 85 SC. Whenever I mount the logic module in the kick panel the car will stall and not start. Apparently when the logic module comes into contact with the chassis it shorts out and the car will not run. Tried different logic modules with the same result. It appears there is a short somewhere in the harness. I looked at the wires going into the LM and it seems OK. Any ideas where to look and troubleshoot?

    Thanks, Ralph

  2. #2
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Car stalls when LM touches chassis

    I would be critical of the connectors. Have you verified that touching a jumper wire from ground to the case won't stall it?

  3. #3
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    Re: Car stalls when LM touches chassis

    inside the LM there should be a piece of plastic sheet .. you can make something from the top of a christmas card box or something similar

    this shields the circuit board from the case

    the LM should mount to the studs in the kick panel .. with TWO INSULATOR SLEEVES ON THE STUDS AND TWO 7/16 PLASTIC NUTS

    for the as now obvious reasons...

  4. #4
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    Re: Car stalls when LM touches chassis

    for the time being it should run just fine laying on the carpet .. I suspect you need the plastic hardware for mounting it.. so you can at least run it until the parts show up

    as long as no one kicks it by accident

  5. #5
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    Re: Car stalls when LM touches chassis

    note the holes in the LM mounting tabs are much larger than the studs ..
    -this accounts for the plastic insulator sleeve between the stud & case material ..caped with the plastic nut
    7/16 ..I remember as it's one of the few std imperial bolt sizes in our cars

  6. #6
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    Re: Car stalls when LM touches chassis

    Ah OK guys. Let me check that out. I do have the plastic nuts but maybe the sleeves are gone. So you are saying that is "normal" that when the board touches the case or the case touches the chassis that it should stall?

  7. #7
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Car stalls when LM touches chassis

    It's bad news for the board to touch the case. If I'm not mistaken, 5digits recommends painting the case back to prevent the board from grounding on it like Dr. Johny Dodge mentioned. Ideally, that wouldn't happen with the design of the plastic stand off section and the end of the board, but it has been 33 years since the last LM car left the factory, so you know how that goes...

  8. #8
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    Re: Car stalls when LM touches chassis

    OK thanks! I fixed it. Put some foam inside the LM for circuit board and thin cardboard between the LM and chassis surrounded by the bag it was supposed to have. Now on to the next issue.

  9. #9
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    Re: Car stalls when LM touches chassis

    new jersey ??
    any holes in the wheel well in front of the LM ?
    next issue will be keepin it dry if so

  10. #10
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    Re: Car stalls when LM touches chassis

    'scuse da double post

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