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93 GMC Sierra Fuel Pump Relay

This is a discussion on 93 GMC Sierra Fuel Pump Relay within the Technical / Maintenance forums, part of the General Discussion category; Had my Truck die on way home about a week ago. Pulled a code 54, Fuel Pump Relay Failure. Jumped ...

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    93 GMC Sierra Fuel Pump Relay


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    Had my Truck die on way home about a week ago. Pulled a code 54, Fuel Pump Relay Failure. Jumped the fuel pump, pump turned on, hit key and it fired. Replaced Fuel Pump Relay and drove it about 300 miles back and forth to work and then died across town. Set up jumper wire and drove it home and now died in driveway. Pump is running with jumper wire but will not start. Bad Pump? Wiring issue? I'll check fuel pressure in a few minutes.

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    Re: 93 GMC Sierra Fuel Pump Relay

    Check the female connections that the relay plugs into. If they are not tight, they will make good contact when cold and as the current travels through it will heat up and expand. Poor contact will cause more amps and the relay can't handle the load and burn up. GM fuel pumps are infamous for the wires that are in the tank to fail due to small gauge wire. But for starters check the connections. If they feel loose, GENTLY squeeze the tabs to close them up a little bit.
    Originally Posted by nebraskaz71

    I fingered where I could fit, few tight spots though and then it kept seeping out all over the place even after releasing pressure. What a mess

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    Re: 93 GMC Sierra Fuel Pump Relay

    Not bad advice but honestly I haven't seen hardly any trouble with the pump pigtails or the relay socket on the TBI trucks. They can be pretty problematic on the Vortec trucks, for sure. Not saying don't check 'em, I just don't rate it high on the suspect level for a TBI.

    Pump may be going bad, or its ground to the frame is crummy, causing extra resistance. The pump power is grounded on the frame rail next to the sender. Don't confuse the pump power ground (black wire w/ring terminal) with the braided ground strap from the filler neck, which is just for static protection.

    Richard

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    Re: 93 GMC Sierra Fuel Pump Relay

    On a whim I jumped the gray pump wire again. Heard the pump again. Fired up. Put the fuse in, runs on it's own, and no code in the computer. On prelim found a pinhole leak in fuel return line. Gonna have to drop tank to see wire connections. Why would it not run yesterday while the pump was jumped and I could hear it running?
    Last edited by Q-Nutz; 10-22-2011 at 11:43 AM.

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    Re: 93 GMC Sierra Fuel Pump Relay

    could be a worn out fuel pump. check fuel pressure to rule it out. 9-13psi.
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    Re: 93 GMC Sierra Fuel Pump Relay

    Right at 13 psi.

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    Re: 93 GMC Sierra Fuel Pump Relay

    read this thread for troubleshooting fuel pump circuit:
    http://www.fullsizechevy.com/forum/g...ting-fuel.html
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    Re: 93 GMC Sierra Fuel Pump Relay

    Well, tank's out. All wiring is good. Only thing that concerns me is on the gauge sending unit there's some bluing between what would be empty to about 1/8 of a tank, like it was getting good and warm. I don't think the gauge sending unit would shut the pump down. Besides I had it jumped, pump was running, wouldn't start, but started next day.

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    Re: 93 GMC Sierra Fuel Pump Relay

    pumps draw more current as they get old, making relays/contacts heat up and go bad and sometimes blowing fuses. if you got the tank out i would replace it.
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    Re: 93 GMC Sierra Fuel Pump Relay

    It's gonna get new lines, pump, and sending unit this weekend.

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    Re: 93 GMC Sierra Fuel Pump Relay

    Sounds like it might be a bad oil pressure switch. I'm pretty sure the ECM only powers the fuel pump relay at startup due to no oil pressure. Once the engine is running, the oil pressure switch keeps the fuel pump powered. Low oil pressure will turn the pump off.
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    Re: 93 GMC Sierra Fuel Pump Relay

    After 2 weeks with new parts, no problems. I assume it must've been the pump.

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    Re: 93 GMC Sierra Fuel Pump Relay

    Guess I was wrong. Died on the way to work. Again pump not running. Hooked jumper wire from pump to battery, heard pump running, still wouldn't start. Came back about 4 hours later, started and ran fine (no jumper). Does the oil pressure switch shut down the pump and injectors? My gauge has always read fine.

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    Re: 93 GMC Sierra Fuel Pump Relay

    The oil pressure switch is not a cutoff device. Read here for a little more info about the circuit...

    http://www.fullsizechevy.com/forum/g...ml#post5487789

    Richard

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    Re: 93 GMC Sierra Fuel Pump Relay

    That's understood now. What could my problem be?

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    Re: 93 GMC Sierra Fuel Pump Relay

    Since you've changed parts, it ran for a couple weeks, and is now giving you trouble again - start the troubleshooting process over. Does it have fuel pressure, how much, does it have spark, etc.

    Richard

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    Re: 93 GMC Sierra Fuel Pump Relay

    Did you ever replace the oil pressure switch/sender? The oil pressure switch runs in parallel with the fuel pump relay, if it is bad, it can cause multiple problems with the fuel pump, regardless of the relay. If the oil sender is not the problem, you may have a problem with the ECM, ECM PROM or wiring.

    First thing I would do is unplug the electrical connector for the oil pressure sending unit and see if you can start the engine. If you unplug the connector and there is oil in the connector, the sender is bad and needs to be replaced. The sender should have 3 wires going to it. Slightly larger orange wire should have 12V on it all the time. The larger gray wire goes to a couple splices in the harness and from there goes to the gray wire on fuel pump relay connector and back to the fuel pump. Check to make sure you have a good circuit to all these places. The last wire is a smaller wire, usually tan, this just goes back to the dash for the gauge.

    If everything for the oil pressure sender checks out, next check the relay. With the relay removed, at the fuel pump relay connector, there is a larger orange wire that is spliced in the harness to the larger orange wire at oil sender, check to make sure you have power here. Next, with the relay still removed, if you have power on the orange wire, you should jumper between orange and gray wires and pump should run. If not, then you have a wiring problem. With the jumper in place, check for power at the gray wire at oil sender and gray wire back at fuel pump.

    Next check the wire from the ECM to the relay connector. I would remove the fuel pump relay and measure voltage on the green wire with white stripe. This should be one of the smaller wires, this is the wire from the ECM that powers the relay, you should not have power here if the key is OFF. Check for power here for a few seconds when you first turn the key ON. If not, then you have a wiring or ECM problem. Also check the smaller black wire, which is the ground for the relay coil. Make sure you have a good ground.

    If all the fuel pump stuff checks out fine, then you may an ignition problem. I would look at the ignition module and the pickup coil in the distributor. Another option is bad injectors, the ECM shuts things down if you have a shorted injector. Unplug the injectors one at a time and try to start the engine. If it starts with an injector unplugged, that injector is probably shorted and is bad.

    Good luck and have a good one!
    "There is no such thing as too much horsepower, as long as you can put it to the ground!!"
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    Re: 93 GMC Sierra Fuel Pump Relay

    Replaced ICM and Oil Pressure switch. I have now noticed the pump runs for a second or two when I shut it off. Haven't had any problems for last 3 weeks or so. Theory: Was running off of Relay only, Relay overheated, pump stopped? Keeping fingers crossed.

 

 

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