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Fuel Pump Relay Removed Truck still runs

This is a discussion on Fuel Pump Relay Removed Truck still runs within the Technical / Maintenance forums, part of the General Discussion category; Hey all, 96 Cheyenne with 305 Vortec. So I was cleaning out my injectors with that apparatus that connects to ...

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    Fuel Pump Relay Removed Truck still runs


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    Hey all,

    96 Cheyenne with 305 Vortec.

    So I was cleaning out my injectors with that apparatus that connects to a compressor and the test valve on the fuel rail to burn off a can of that special injector cleaner stuff. Of course to do this, the fuel pump has to be disabled.

    I took the fuel pump relay out, and the fuel pump still ran. I had to unplug the power right from the harness going to the pump.

    I looked all over the truck for a fuel pump fuse and didn't find any. There was no air going to the apparatus at the time and it was holding the usual 50-60 psi of pressure.

    So it seems it runs without this relay in, so what exactly does this relay do? Is it just for priming? It ran for about 10 mins before I realised the pump was still running.

    Anyone have any ideas?

    Thanks!

  2. #2
    Supporting Gold Member GreaseDog's Avatar
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    Re: Fuel Pump Relay Removed Truck still runs

    probably pulled the wrong relay, since the same relay is used for several other things on the truck.
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    FSC SOUTHEAST CHAPTER kirk's Avatar
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    Re: Fuel Pump Relay Removed Truck still runs

    Quote Originally Posted by GreaseDog
    probably pulled the wrong relay, since the same relay is used for several other things on the truck.
    X2
    It can't run without the relay, since it won't run the fuel pump. There should be a picture on the fuse panel lid showing what each relay and fuse is for.
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    Re: Fuel Pump Relay Removed Truck still runs

    Fuel pump relay will either be in the panel under the hood, or in the side of the dash when you open the drivers side door.


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    Re: Fuel Pump Relay Removed Truck still runs

    What kept it running was the fuel pump oil pressure switch.
    When you build enough oil pressure this switch makes and
    passes 12v to the fuel pump.
    88 Ext. cab longbed TPI 350
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    Re: Fuel Pump Relay Removed Truck still runs

    probably pulled the wrong relay, since the same relay is used for several other things on the truck.
    Thats what I thought but I double and triple checked the relay against the fuse and relay map on the underside of the cover.

    It can't run without the relay, since it won't run the fuel pump.
    Thats what I thought too.

    Fuel pump relay will either be in the panel under the hood, or in the side of the dash when you open the drivers side door.
    I got this relay from under the dash. Driver side, big relay and fuse box.

    What kept it running was the fuel pump oil pressure switch.
    When you build enough oil pressure this switch makes and
    passes 12v to the fuel pump.
    Now this is interesting. It would make sense since there are several wires going to this switch.


    Thanks for all the info!

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    I LOVE THE SNOW!!! GIMECHANIC_454's Avatar
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    Re: Fuel Pump Relay Removed Truck still runs

    you could have tunred the key on and and pulled the relays out untill the fuel pump shut off


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    Re: Fuel Pump Relay Removed Truck still runs

    Not only will the truck run with the relay pulled, it will START with the relay pulled. Don't believe me, go try it! It will spin over for a long time until your oil pressure comes up enough for the oil pressure switch to power up the fuel pump circuit. Check the wiring diagrams, or just go out and try it.

    Anyway, correct relay for the later OBS (95-up with the underhood convenience center on the driver's fender well) would be the one at the very front corner of the panel. (It seems like a while back I posted "front corner facing the driver's side" but I decided this morning to take my worthless 4 hours worth of sleep self outside and check one just now, and saw that's the side the maxi-fuses are on...)

    Richard

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    Re: Fuel Pump Relay Removed Truck still runs

    I agree, my truck will start and run with the fuel pump relay removed. I was trying to dry up the cylinder by removing the pump relay and cranking the engine, this didnt work as the fuel pump still operates even with the relay removed.

    Mines a 1997 model.

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    Re: Fuel Pump Relay Removed Truck still runs

    Yeah mine runs with it pulled too. I never understodd why until now.
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    Re: Fuel Pump Relay Removed Truck still runs

    Thats why the book tells you to remove the f/p fuse.
    88 Ext. cab longbed TPI 350
    99 Suburban LS Vortec 350
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