87 gmc not getting fuel to start

Discussion in '1973-1987' started by 450r, Oct 27, 2013.

  1. 450r

    450r Member

    Joined:
    Oct 27, 2013
    Messages:
    1
    New guy here any help would be greatly appreciated! I have an 87 gmc 2500 4wd 5.7 350 with the TBI. Just bought this truck it quit the previous owner suddenly and he didn't wAnt to mess with it. All I know for sure is it has a new fuel pump and fuel pump relay the truck did originally have two tanks for whatever reason currently it just has driver side tank when u turn the key I can not here the pump run at all it turns over fine just for some reason will not get fuel to fire if I run a hot wire down to jumper the pump I can make it run and get the truck fired an idling just fine I started chasing wiring under the bed over to the tank selector valve found some bAd wires fixed the problems And still nothing cld it be something as simple as a fuse or ground I'm missing keeping power from getting to the pump while trying to start the engine . The switch in the cab is selected to the correct tank. Any tips to head me in the right way?? Thanks in advance
     
  2. nerfherder78

    nerfherder78 Member

    Joined:
    Aug 15, 2003
    Messages:
    324
    Location:
    Fairfield, CA
    There is an oil pressure switch that interrupts power to the fuel pump relay when there is no oil pressure (in the event of an accident/fuel leak).

    If you apply 12v across the trigger side of the relay (D and F pins on img below) and the truck starts normally, the ops is likely the culprit.
    [​IMG]
     
  3. 87squarebody

    87squarebody Member

    Joined:
    Dec 10, 2013
    Messages:
    1
    Try the selector switch in the dash. Make sure it is connected and fully depressed. I had the same exact problem, bought new fuel pumps, relays, tracing out wires and it turned out to be a 10 dollar selector switch.
     
  4. Doobler

    Doobler Member

    Joined:
    Apr 4, 2021
    Messages:
    1
    I wish these posts would not just end before the solution was posted, I am having similar issues and I guess I am just going to copy and paste what I have going on in hopes someone can help me before I lose my mind.

    I have an 89 chevy 1 ton crew cab (I think it was an old forest service truck) it is the older style square body, 350 tbi model with the fuel module unit. To tell a little back story, I had not driven the truck in a few years and was thinking about selling it. I charged the battery and fired it up and took a video to send to the person interested but never ended up wanting to sell this old girl. Months later we where going to move and I had planned on getting the truck rolling and limping some loads to the new place but when I went to start it, it would just crank and not fire off unless I threw gas down her throat. Thinking it was something simple like a bad fuel filter getting clogged from the last time I started it with old gas in it but the new filter did nothing. I later realized I was not hearing the fuel pump at all so I changed the pump relay hoping for a quick fix so we could get moving but that did nothing as well. We ended up towing it to our new place so I could either figure it out or get rid of it later. I was testing the relay and replay plug to see if I was getting power which I was and could hear the relay click. Fuses are all in order as well. Going through some grounds in the front and cleaning them up did not set anything straight. One day I had been checking wires and went inside to mess with the tank selector switch and thought I would turn the key on and listen for a pump and I heard it for the first time! I fired the truck up and let it idle for a bit while I went inside just to hear it slowly surging itself to sleep when I came out as it seemed the fuel pump stopped working again and could not get it to fire up. turning the key on and off I got it to come on again and after it did not fully fire I then heard the 20 sec fuel module signal pop on and was able to get it running for a tiny bit once again. During this I was trying to get the fuel tank to switch but it would just kill the truck either from it not doing it correctly or the tank being empty or that pump just not working. I have never been able to recreate the truck firing up after that sadly and I have gone back and messed with some connections and the tank selector switch with no luck. I am getting power to the relay and I am getting power up to the tank selector switch. I probed the tank switch plug and I tested the tan/white (C) power to the other 3 (ABD) plugs and got around 11-12 volts testing it with each of those plugs (Not sure if ALL of them are supposed to read like that or not?) I am not very knowledgeable when it comes to electrical so I am baby stepping myself through what I can. A few other things to add: The fuel gage always reads way past full no mater what tank the switch is on (RH tank was the only one working when it fired up anyways) and I also had replaced the ignition control module a while ago but that was obviously fine. I am trying to get this thing running so I can do some work around my property without spending a arm and a leg replacing the usual string of parts people do when troubleshooting these types of issues. Any assistance would be greatly appreciated.
     

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