1998 Suburban 5.7l TBI. ECM-B fuse blows

Discussion in 'GMC Truck Forum' started by PatriotYS, Aug 22, 2012.

  1. PatriotYS

    PatriotYS Member

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    New to the forum and hoping to get some here.
    Just replaced the flywheel and got everything back together. As soon as I connected the battery back up, the ECM-B fuse blew. Replaced fuse and it did it again. Visually checked all plugs and wires I disconnected in the flywheel repair and found nothing bad, i.e. loose connection, wire harness cut or exposed wire. Broke out the schematic and it looks like ECM-b drives fuel pump relay to pump and also interacts with ECM. I removed relay, dropped tank and disconnected both fuel pump plugs, and all four plugs into the ECM. Fuse still blows. I know the ECM-B fuse is hot full time. I have traced the wire from the positive terminal to the main fuse block in engine compartment and have zero voltage drop from battery to ECM-B fuse plug hot.
    I noticed the emergency flasher push button was broken on the steering console so I am replacing the turn signal assy although I don't think it is related.

    I think I have a direct short to ground but do not know where to look from here.

    I guess my next step is to ohm the wire from battery to main fuse block. Then try to take apart the main fuse block and see if there is an internal short on the connections on the back.

    Any help I can get tracking this down and resolving is greatly appreciated. I already have 7 hrs it already.

    Thanks!!!! :help:

    Tom
     
  2. chevychase

    chevychase Semi-Admin
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    Usually this fuse will blow if fuel pump is getting ready to go bad. Seems you disconnected and still blows.
    Did this after trans work..i would look for a pinched wire /bare wire somewhere in that area.
    Look at bell housing area . Has to be in the fuel pump circuit.
    Welcome to the forum patriotYS
     
  3. PatriotYS

    PatriotYS Member

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    Thanks Chevychase. I was hoping you would respond.

    The Tranny harness was the first thing I thought after doing tranny work. Looked over all the wires in the harness that runs on top of the bell housing up the firewall. Nothing visually poped up.

    Do I need to trace the fuel pump harness back to the fuel pump?
    Where do I start?
     
  4. chevychase

    chevychase Semi-Admin
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  5. chevychase

    chevychase Semi-Admin
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    [​IMG]
     
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  6. PatriotYS

    PatriotYS Member

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    This condition did not occur until after flywheel replaced which had always had me suspecting it has something to do or in the vicinity of the tranny. I've seen stranger things unrelated things happen....like change oil and heater stops working.

    Since the fuel switch is located aft of the distributer and nearest the area where the tranny work was done, I can start there. I will go over every wire tomorrow and check plug on fuel swich and might as well replace the switch while I'm there. Do these switches fail and cause this condition ?

    My crappy Haynes manual schematic looks different and doesn't show the oil press/fuel pump sw-sender. That's pretty frustrating trying to resolve an issue and the guidance isn't complete. BTW...Neither of our schematics shows any connection to the electronic brake controller module. Should I unplug the ECMB also?

    Thank you for this help. I've got my work lined up for tommorow and will report back results.
     
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  7. chevychase

    chevychase Semi-Admin
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    No do not have to fool with it..it is in the pics for reference.
     
  8. PatriotYS

    PatriotYS Member

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    By my logic, if I pull all the plugs to components in the ECM-B circuit ie...VCM, fuel pump sw/oil press, ECBM, fuel pump and put relay back in, if the fuse blows then it a chaffed hot wire grounding out and not necessarily a bad component.

    If fuse stays intact, plug components back in one at a time. IF blows, last component bad. Continue until cicuit complete.

    Sound correct?
     
  9. PatriotYS

    PatriotYS Member

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    Just to be clear.....fuse blows as soon as battery connected. Key NOT in ignition. It also blows with the relay out of the fuse panel. That fuel pump sw looks like it controlled by vcm. With vcm unplugged, no power should be getting out there thus short to ground.

    That is what is confusing me....fuse blows with fuel pump relay out and vcm disconnected. I am assuming with those two disconnected, no power goes past there to rest of circiuit.....ie fuel pmp/oil press switch and fuel pump in tank.

    I need a drink bad....
     
  10. chevychase

    chevychase Semi-Admin
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    Now i,am confused as you are?? The relay center will be hot all times looking at diagram...you have a pump prime connector coming out of
    The relay center might be touching somewhere. I think it is around brake booster area. Will be a single red wire.
    Some how i think it is a pinched wire.
     
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