Fuel Pump Issue

Discussion in 'The Garage' started by randy88k5, Jan 10, 2007.

  1. randy88k5

    randy88k5 1/2 ton status

    Nov 8, 2004
    Likes Received:
    Lynchburg, VA, USA
    Well, I thought I had a fuel pump going bad. I replaced it with a factory unit about 5-6 years ago. I replaced the tank last fall due to some pinholes, and I opted not to replace the pump when it was out.

    It usually starts up like it normally does the first time. If I drive for about 10 to 15 minutes, turn it off, it doesnt want to start up again. I have to crank it and pump the pedal like a carb, and usually starts after about 7-10 seconds. I was kicking myself for not replacing it when I had the tank out last fall.

    I gave it a tune-up, and used WinALDL to test sensor readings. Everything seemed normal. So I bought another pump.

    To make draining easy, I decided to disconnect the fuel line and drain the fuel directly into gas tanks because I know the pump somewhat works. The fuel was draining very slow, about 15 minutes for 2.5 gallons. I have about 15 gallons in the tank. I pulled fuses and relays to keep the drain on the battery minimized because I knew it would be running for a while.

    It filled a few other gallons, then stopped. I gave the pump a rest, tried again. Nothing. Tried cranking, still plenty juice left in the battery. So I tried to use the jumper connection on the firewall to bypass the relay. Then the pump really started pumping, probably a good 5 times more flow.

    Does this sound like a bad fuel pump relay? I know the oil pressure switch should be good, cause I replaced it the same time I replaced the pump before. It doesnt look like a high-wear item. I dont have a spare relay with me, as they are at my house (Im at my parents right now). What do you all think?

    '88 350 TBI

    Thanks for looking...
  2. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
    Likes Received:
    Roy WA
    Randy, since it's the same wiring to the pump, I might try running it for the length of time you seem to be able to get it to work as is, with the relay bypassed. Just to make sure you don't have some sort of weird wire issue going on. The oil pump switch SHOULD keep it running normally if the relay is disconnected or intermittently dies, I'd like to see this tested if you could. (With it running, can you pull the relay connector and the engine still runs, and if yes or no, will it start with the relay disconnected?) That would answer the question as to why restarts take so long, it's the oil pump pressure coming up. Bypassing the relay with a jumper at that point would probably tell you the same thing. Instant start=likely bad fuel pump relay.

    If anyone else reads this thread, wondering why you couldn't replace the GM fuel pump relay with a heavier duty one, in Randy's case perhaps the same style as for your fans. :bow: I'd like to do that one myself, all three relays being the same would be the ultimate in redundancy.

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