fuel pump problems, please help!

[Sjconner]

1993 z71 Ex Cab.
4x4 Tbi 350

Okay so about a week ago I had my M.A.P sensor go bad. Well I didn't know it and I replaced my fuel pump fuel & filter.
After I got my problem fixed with the sensor all was good.
Well 2 days ago I was driving and the truck just died. It turns over fine. But I immediately noticed my fuel pump wasn't turning on. so I replaced the relay. The fuse was good. Still the fuel pump wasn't kicking in. So I got out my meter. The fuse gets 12 volts. When you first turn the key to the ON position. The fuse relay is getting 12 volts also. But when I go to the plug on the fuel pump (4 pin) there are 2 black wires. One ground the other I'm Not sure, a white, and a red.
The black and red get no power to them ever. When the key is first turned on. Or after its on. The white wire(middle wire) gets 8.49 volts constant. But I assume that's the gas gauge wire, since my gauge still works.

Any advice will be greatly appreciated!
-Jake

 

[DGA1]

When you first turn the key to on, do you hear the pump cycle at all? I don't know much about the TBI trucks, but any other fuel injection system primes the fuel system by running the pump for a few seconds first, then if the engine is not actually running turns the pump off. Maybe someone with TBI experiance can chime in and say something to the accuracy of this on TBI trucks. You can cycle the key on and off as many times as you wish and the pump should come on for a short interval each time you do this. In short you could have gotten yourself a faulty new pump if you don't hear it at all.

 

[Sjconner]

Yeah, I know thats what happens when you turn the key forward. And no The pump doesn't cycle or prime. And I considered it being a bad pump. But I thought it was strange that only one of the wires that goes to the pump had power. And only 8.49 volts.

 

[DGA1]

Like you said, that might be the voltage source for the fuel level gauge. I just got a factory service manual for my '96. Next time I'm home I'll check it and see what it says for it and maybe the TBI trucks are not far off from that.

Maybe someone can flip the key to on while you have the meter on the pump wires and see what happens during the prime cycle?

 

[gmcyukondriver]

Have you checked the power at the fuel relay? Under your hood, there's a fuse box. One of those is a fuel relay (check your manual). I'd look there. They're cheap and easy to replace if it's bad.

 

[chris209]

Sounds like your relay is bad. If I'm not mistaken the power flows from power source to fuse to relay to pump. The relay would stop the pump from priming if it was bad. Its like a light switch in a house. The ignition acts as a finger. Relay is the switch and pump is the lightbulb.so to recap. Turning ignition switch on will send signal to relay which powers up pump. Check the relay.probably faulty

 

[96-1500]

Sounds like your relay is bad. If I'm not mistaken the power flows from power source to fuse to relay to pump. The relay would stop the pump from priming if it was bad. Its like a light switch in a house. The ignition acts as a finger. Relay is the switch and pump is the lightbulb.so to recap. Turning ignition switch on will send signal to relay which powers up pump. Check the relay.probably faulty

He said he already replaced the relay.

I would get out and have a close look at the wires for possible corrosion. In my area (salt country) it's a not uncommon problem to see wiring issues at the back end of these trucks.

Sent from somewhere between here and there

 

[silverado13]

proabably the best investment i have ever made for my truck was a electronic fuel pressure gauge on my pillar, being able to monitor the fuel pressure has saved me so many times

 

[scoob8000]

Pull the relay and use a short piece of wire to connect the fused feed to the output terminal that goes to the fuel pump.

The two terminals should be diagional from each other. Usually if you look at the bottom of the relay you'll see some number.

The sockets that match up with #87 and #30. One of those will be the power feed and the other will go to the pump. If you jump them together see if the pump runs. Just lightly touch the wire at first and be prepared to yank it off it there's a short.

If the pump doesn't run, I'd say it's the pump or a wiring issue.

 

[98_k1500]

Pull the relay and use a short piece of wire to connect the fused feed to the output terminal that goes to the fuel pump.

The two terminals should be diagional from each other. Usually if you look at the bottom of the relay you'll see some number.

The sockets that match up with #87 and #30. One of those will be the power feed and the other will go to the pump. If you jump them together see if the pump runs. Just lightly touch the wire at first and be prepared to yank it off it there's a short.

If the pump doesn't run, I'd say it's the pump or a wiring issue.

THIS