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MSD 6A box install - Ground Signal issue

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    MSD 6A box install - Ground Signal issue

    Ok, so I installed a MSD 6A box and blaster 2 coil... yeah yeah yeah i know there are no power gains to be had, blah blah blah thats not why i did it (just so we don't waste time going through that part)

    After troubleshooting it for a while with MSD on the phone and many tests and hooking it up to a 2nd battery, we found that the voltage in the battery was under 12 so the box was not staying on.

    So battery charged up, and with good main + and - connections I tested it by pulling coil wire from distributor, put it 1/2" in from ground, then manually grounded the white trigger wire. When this is done the box/coil fire. So i know the box/coil works as it is wired if ground is triggered.

    Now when the trigger wire is connected to the wire that was the - coil wire that the DME uses to trigger ignition, the car will not start. So that leads me to believe that the DME is not grounding that wire like it should. Any ideas where i can start looking/testing for this? Or another way to wire? Thanks for any help you guys can provide!
    1989 325is - S52 Turbo Swap
    1995 M3 - SCCA CStock AutoX Car
    1991 318is - M20 swap - 5spd(SOLD)

    #2
    Ok so after further troubleshooting it seems to be an issue with the ground signal from the ECU. All running troubleshooting tests for no start the car passes all of them, and injectors are firing just no spark. Ground wire (orig - coil wire) has perfect continuity from DME pin 1 to the end at the coil. I swapped to another DME and still no fire. Coil? other ideas?
    1989 325is - S52 Turbo Swap
    1995 M3 - SCCA CStock AutoX Car
    1991 318is - M20 swap - 5spd(SOLD)

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      #3
      I would guess that the current flow required to fire the stock coil is higher than that required to trigger the MSD, but the pulse width could be too narrow to trigger the MSD. Seeing oscilloscope traces of the firing signal for the stock coil and for the MSD would be illuminating.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

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        #4
        update...
        figured it out...

        Ground signal wire had perfect continuity, but the resistance was off and there must have been a short to ground with it so the signal wasn't making it. Ran a new wire and boom! she fired right up with the MSD box!

        Thanks all for the help!
        1989 325is - S52 Turbo Swap
        1995 M3 - SCCA CStock AutoX Car
        1991 318is - M20 swap - 5spd(SOLD)

        Comment


          #5
          Do you have a wiring schematic for this? Can you draw one for us for reference? Thanks

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