???---Question for GM mechanics

Discussion in 'Shop Talk' started by mdharris68, Oct 30, 2006.

  1. mdharris68

    mdharris68 Well-Known Member

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    I have a 90 chevy sub 1/2 ton 350 4x4 and am looking for the fuel pump relay if there is one. I am not getting power to the pump as far as I know. My manual is vauge on whether there is one or not and I am not great at reading schematics. Any help greatly appreciated. Thanks.
     
  2. skruzich

    skruzich Well-Known Member

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    Fuel pump relay is in the fuse box under the hood on the drivers side. It's location will be labled on the lid of the box.

    It's a square module. There usually is another relay in the same box that has the same numbers as the fuel pump relay so i would take one of those and plug in to see if your fuel pump primes and operates before spending the bucks to replace.
    IF you find that inserting another relay don't work, start looking for a broken wire, or if you have been working on the engine, look for a ground wire that you forgot to bolt back down.
    Most of the time you have troubles like that, is because of a bad ground.
    If you can't find a ground you can fix it by soldering a ground wire to the ground terminal on the fuel pump side of the relay and that will reestablish ground.
    If it still doesn't work at that point start looking at your fuel pump.
     

  3. mdharris68

    mdharris68 Well-Known Member

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    Thanks, I think I made the mistake of changing the fuel pump prematurely. I was having all kinds of problems that led me to believe the fuel pump was bad but do not know enough to troubleshoot in the correct order. I took out the fuel pump and replaced it, so I will begin where I should have and look at the electrical side of things. Thanks for the advice. MDHARRIS68
     
  4. skruzich

    skruzich Well-Known Member

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    Make sure you didn't forget to hook up the ground on the fuel pump sending unit. There should be three or four wires coming out of it, and one of them is grounded to the frame.

    Like i said before, the only thing left is the ground wires and if no ground is bad then all thats left is the ECM
     
  5. mightybooboo

    mightybooboo Well-Known Member

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    By relay do you mean the switch that shuts off the power in an accident? Some cars have a resettable fuel pump power switch,located in the trunk area.A good enough thump can shut them off.

    BooBoo
     
  6. skruzich

    skruzich Well-Known Member

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    Pick up trucks don' t have trunks

    :p


    Besides, fuel pump relay is used to turn on the fuel pump so fuel pressure builds. The ecm or computer needs the pressure at X before it can fire the injectors or throttlebody injectors, to get the engine started. Once the engine starts the oil pressure switch will take over and release the fuelpump relay once the oil pressure builds to over 4 psi. That in itself is a safty feature so you don't blow your engine if the oil pump fails. It will cut your engine off if it fails.
    The relay comes on when you turn your key ignition on and primes the pump. You can hear the fuelpump motor when you turn the key on for a second.
     
  7. mightybooboo

    mightybooboo Well-Known Member

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    Look for the Fuel Pump Inertia Switch,its resettable,also check the fuses for the relay.I'd call my local chevy dealer and ask them about em.

    Are you not getting any voltage to the fuel pump? You tested it?

    BooBoo
     
  8. dodgewc

    dodgewc Well-Known Member

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    There is no inertia switch on your truck. Ford is the only one who uses that. FP relay should be in a junction block somewhere in the right side of the engine compartment. Unfortunately I only have Michell On-Demand available to me on this old of a model ( Okay, it may not seem old to ya'll, but that is all that is available to me, and I work in a GM agency) P.S. Mitchell sucks! Alldata is a tad better, but not much of a tad. There may be a fuel pump prime connector located near the battery. It's green. Jump 12 VDC to it, if it's there, to power the pump.Wish I could read these crappy diagrams avalable to me, would point you much better.
     
  9. skruzich

    skruzich Well-Known Member

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    Well some of them have a fuel pump prime. I spent a while the other day looking for one on a 89 model. SHeesh. I finally gave up took a extra relay i had in the box that i popped the cap off and squeezed the contacts together to test the fuel pump.