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Thread: 1987 throttle body fuel pump problem

  1. #1
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    1987 throttle body fuel pump problem

    I have a 1987 k10 4.3 v6 full size fuel injected truck. About two months ago I was coming to work in a heavy rain. When I got out of work that nite (i work 2nd shift) I could hear my fuel pump running. Well It started and when I went home it was still running 3 miniutes after I shut it off so I disconnected the battery. Next day I replaced the fuel pump relay on the firewall no difference. The fuel pump runs even with the relay disconnected! Well when everything dried out it went back to normal operation. The other nite it rained and it drained the battery. fuel pump running continuously. I figure the pump is energised and the relay makes the ground? Haynes manual is no help wiring dia does not even show a fuel pump. Were can I get a wiring diagram for my truck? Have any of you ever seen this before?

    Fred

  2. #2
    Senior Member chevyguy's Avatar
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    The fuel pump relay is the control circuit. it is somehow closing the contacts when it gets wet. Try to pull the fuel pump relay next time it does this and see if it turns it off. This will help with diagnosis
    Window tint its for window, Not for tail lights. Don't be that guy .

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    even with the fuel pump relay disconnected the pump still runs.

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    Does anyone know where I can obtain a wiring diagram for my truck? 1987 k10 4.3 v6 throttle body?

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    Senior Member chevyguy's Avatar
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    Chilton manual. Sounds like you are gonna need to take electrical readings(voltage and resistance) to find this one.
    Window tint its for window, Not for tail lights. Don't be that guy .

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    thanks, I will

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    So a newer haynes manual had the throttle body wiring diagram power runs from relay to engine oil pressure switch and ecm. Since it continues to run with the relay removed I am fairly certain I have a problem with the oil pressure switch or the ecm itself. I will unplug the oil pressure switch the next time it happens. Maybe it is stuck in the on position? Once oil pressure is made is that where the fuel pump gets 12v from?

  8. #8
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    Oil pressure shouldn't turn your pump on or off, because the pump runs when you turn your key to the on position without starting the engine, and there is no oil pressure then.
    It used to be a Jeep thing, you wouldn't understand.

  9. #9
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    Well today I went out to my truck and hooked up the battery cable and fuel pump immediately started. I climbed under the truck and tapped on the oil switch and fuel pump stopped. I think it uses the relay to start initally and then as long as you have oil pressure the fuel pump runs. Oil switch sends info to ecu, ecu powers pump. thats my best guess anyway. I have a new switch ordered.

  10. #10
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    Good call, I never thought of it that way.
    Glad to see that you fingered it out!
    It used to be a Jeep thing, you wouldn't understand.

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