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  1. #1

    Default How bad did I kill it?

    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!
    Joe

  2. #2

    Default

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

    2004 SILVERADO 2500HD LS
    Pro Comp Leveling Kit
    285-75-16 Cooper ST All Terrains
    Pro Comp Programmer
    Bilstein Shocks
    Linux Bed Liner
    Tinted Windows



    Other rides:

    1967 Landcruiser <350 Chevy>
    1970 Camaro
    1990 Geo Metro Convertible
    2007 FJ Cruiser

  3. #3

    Default

    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!
    Joe

  4. #4
    Sr. Apprentice brianj's Avatar
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    Default

    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. #5

    Default

    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.
    Jim

    2004 SILVERADO 2500HD LS
    Pro Comp Leveling Kit
    285-75-16 Cooper ST All Terrains
    Pro Comp Programmer
    Bilstein Shocks
    Linux Bed Liner
    Tinted Windows



    Other rides:

    1967 Landcruiser <350 Chevy>
    1970 Camaro
    1990 Geo Metro Convertible
    2007 FJ Cruiser

  6. #6

    Default

    Quote Originally Posted by brianj View Post
    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!
    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.
    Jim

    2004 SILVERADO 2500HD LS
    Pro Comp Leveling Kit
    285-75-16 Cooper ST All Terrains
    Pro Comp Programmer
    Bilstein Shocks
    Linux Bed Liner
    Tinted Windows



    Other rides:

    1967 Landcruiser <350 Chevy>
    1970 Camaro
    1990 Geo Metro Convertible
    2007 FJ Cruiser

  7. #7
    Sr. Apprentice brianj's Avatar
    Join Date
    Oct 2009
    Location
    New Hampshire
    Posts
    68

    Default

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

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