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How bad did I kill it?

Discussion in 'General Chevy & GM Tech Questions' started by joescott, Oct 17, 2009.

  1. joescott

    joescott New Member

    Hello all.
    Thanks for this great site. I have a 1987 GMC suburban with a 350 engine. I rebuilt the engine (something I have not done in around twenty years) and think that is probably ok. During installation, I did inadvertently install the battery backwards.
    Other than the really awesome fire from the alternator, I am also blowing the "emcb" fuse with the key in the off position. because It is cold and rainy out right now I don't feel like digging into it at the moment. The haynes manual wire diagram indicates I may have taken out the "ECM". Does this seem reasonable? Or is a wire short more likely?

    Thanks in advance!
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    An easy way to find out is to unplug the ECM and see if the fuse still blows.
  3. joescott

    joescott New Member

    Thanks Jimmiee.
    I did as you suggested. With the ECM unplugged, the fuse does NOT blow. When I plug it in, it blows right away. This would indicate the ECM is bad, OR something the ECM drives is shorted. The ECM can be had for around $80 so I will take the gamble that it is what is shorting.
    Thanks for your help!
  4. brianj

    brianj Rockstar

    Nothing is realy "driven" by the ecm- it basicaly tells everything else what to do. I suppose it is possible to have a bad relay that is driven by the ecm signal, but I doubt it. This is a good example of why I still like points, though!
  5. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Next step is to check the fuse wire to the ECM. With ECM unplugged the wire from the fuse should test open with an Ohm meter. If the wire is open the ECM is probably shorted. If the wire is grounded <Short> then you need to replace the wire or find the short. Sometimes it's easier to just replace the wire rather then trying to find the short but it's up to you. Do not replace the ECM until you have fixed this wire.
  6. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The GM ECMs do have drivers. They are called Quad Drivers. They provide the ground to a solenoid or other accessory to turn it on or off. The Quad Driver is self protected similar to a circuit breaker. So if there is a short to ground the Quad Driver will stay open until the short is repaired. So Quad Drivers protect the ECM from damage. :glasses:
  7. brianj

    brianj Rockstar

    Got me on that one. This is also a good example of why I quit being an auto mechanic in 1995.:neutral:

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