Fuel pump issue again.

Discussion in '1976-1983 Build-Up/Project Threads' started by nottoshabi, Jan 13, 2020.

  1. nottoshabi

    nottoshabi Enthusiast

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    The fuel pump is not turning on again. I replaced the fuel pump but it wont turn on when connected to the power source, there is a current coming out of the connector and the fuel gauge reads but the pump wont come on. Any one ever had this issue?

    The pump works I connected it directly to the battery also connected the whole fuel assembly to the battery and pump still wont turn on. Im stuck here I don't know what to do. Im thinking of installing an external fuel pump unless you guys have better ideas?
     
  2. Pearce

    Pearce Enthusiast

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    I would check your pump wire. Kind of sounds like it's the problem if you already bench tested. Probably going to need to run a new wire.
     
  3. nottoshabi

    nottoshabi Enthusiast

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    Are you referring to the 2 wires in the fuel assembly unit inside the tank?
     
  4. fred heath

    fred heath Veteran

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    Your fuel pump will only run with the ignition in the “start” position(if the engine isn’t already running). Simply turning the key to “on” will not power the pump. Your oil pressure sender is tied into the fuel pump circuit as a safety measure. In the event you loose oil pressure, the fuel pump will shut down.
    You should see a yellow with black striped wire coming from the oil pressure sender to a plastic connector on the passenger inner fender. Disconnect this wire(at connector). You should now be able to hear the pump cycling with the key in the “on” position. If nothing happens, the problem is something else. Don’t forget to reattach the wire when done.
     
    Last edited: Jan 14, 2020
  5. nottoshabi

    nottoshabi Enthusiast

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    @fred heath Thank you for the info on the oils pressure sender. I actually connected the fuel sending unit to the battery directly and did not get the pump to turn on. When i connected the pump to the battery then it turn on.
     
  6. fred heath

    fred heath Veteran

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    Not sure what you mean by “fuel sending unit”. You may have a problem with the supply wire from the switch to the pump.
    Worst case, find an “ignition on” supply source (wipers?) and tie that directly to the fuel pump supply wire. Not the way it should be done but should get you up and running.
     
  7. MrDinkleman

    MrDinkleman Veteran

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    Looking at a wiring diagram for a 1979 Celica, the oil pressure fuel pump safety switch is a ground, not a power source. So you need to just ground tha wire. I am guessing the safety switch is the same in the trucks.
     
  8. nottoshabi

    nottoshabi Enthusiast

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    @fred heath I dropped the tank and removed the unit (fuel sending unit) that holds the pump and the float that tells how much gas there is in the tank. I connected that unit directly to the battery and got nothing, connected the pump to the battery and the pump runs. From the wire that connects to the unit coming out of the truck there is a pulse coming out of it when the key is turned to the start position.

    The wires that are connecting the pump to the unit. The ones that sit in the tank look old, the plastic around the wires is dried and is flaking off. I think that what @Pearce was talking about. Would that disrupt the flow of electricity?

    I have uploaded a picture of what the fuel sending unit looks like. With out the pump.
     

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  9. fred heath

    fred heath Veteran

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    It’s been awhile since I changed my pump, so bear with me.
    If I understand you correctly, your new pump motor runs when you attach the pigtails to a 12V supply but not when installed in the tank. This shows the pump is good so it’s in the wiring to the pump or the pump relay. You also have a resistor which could be bad. My guess is the wiring. If you have dry flaky wires inside the tank that could be your problem. Everything inside the tank has to be liquid tight. Try running new wires and use heat shrink tubing on all splices. You could even slide the heat shrink over the flaky wires if you can’t replace them.
    It’s hard to “armchair quarterback “ these types of repairs. I would buy the Haynes manual for your truck and follow the troubleshooting guide for the pump.
    I like the Haynes manual because it includes the electrical diagrams for the truck and subsystems.
     

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