Have to bump throttle to keep running. Won't run at any steady RPM.

[PlayingWithTBI]

I didn't want to drop the tank, but it seems I can't avoid it.

Another way to do it is to remove all the bed bolts on the left side, loosen the bolts on the right, unhook wire harness to the tail lights, fill spout and ground wire(s) there, then jack up the left side of the bed and block it up high enough so you can reach the sending unit on top of the tank. If/when you replace the fuel pump don't forget a new suction sock too.

If the gas gauge is pegged past Full, the wire harness is probably broken somewhere between the gauge and the sending unit in the tank.

And this could be contributing to your issue with fuel pressure if, as Schurkey said, you're not getting proper power and/or ground.

 

[Schurkey]

And this could be contributing to your issue with fuel pressure if, as Schurkey said, you're not getting proper power and/or ground.

There's four wires to the fuel tank "hanger": Power and ground for the sending unit, power and ground for the pump.

The indications are that his harness is not in good condition, and that could affect the pump. However, the actual wires are separate, not shared. The sending unit wires can be cut, broken, damaged--and not affect the pump wires.

 

[PlayingWithTBI]

However, the actual wires are separate, not shared. The sending unit wires can be cut, broken, damaged--and not affect the pump wires.

Understood, I'm just saying it could. Like if you see only one cockroach, chances are there's more lurking around in the dark.

 

[Hoot Gibson]

Thanks for the road forward! It looks like I'm going to be checking some wiring, which I hate, but it's better than spending a bunch of money on parts, only to have to do it after parts don't fix the problem.

I checked the fuel pressure gauge because I thought it odd that the engine would run at all with no pressure. I used to work on test equipment, so I'm used to TE being a problem as often as an actual malfunction in the thing being tested. Old habits die hard.

I looked at some videos about changing the fuel pump, both dropping the tank and raising the bed, and it looks like dropping the tank is most likely the way I'll go. The bed bolts are pretty rusty (it used to be a work truck in Key Largo, and it's got lots of salt water corrosion on the bolts). The tank was dropped a couple of years ago, so it's been out recently. That might have contributed to the wiring problems too. The shop wasn't that great.

I really appreciate the tips on where to start looking at the wiring. I used to fix aircraft, boxes and wiring, but never had to do much on a truck. Knowing where to start is a big help.

It may be a while, but I'll report back when I figure it out. Or before that, if I get stuck again.

Have a great New Year!

 

[AuroraGirl]

I haven't (seriously) turned a wrench since carburetors and points, so I'm at a loss.

1994 C1500 Silverado 350 TBI automatic. Seldom used ethanol.

The truck sat for 6 months or so. When I tried to start it, it did the below. I drained the gas, put in fresh, and changed the fuel filter.

It starts and dies immediately. Does this every time. However, if i bump the throttle at start, it will raise the RPMs. Then it dies. If I bump the throttle continuously, it will keep running. It won't run at a constant RPM, I have to keep revving it up and letting it come down, then rev it up again before it dies.

Any ideas? Thanks in advance!

sounds like a minimum air speed / IAC relearn is in order. I would clean the IAC, check the connector, and check the... throat..? of the TB. I dont know much on TBI but at least verify your air valve, the IAC, is clean and is good connection. I almost wonder if its sticky or not responsive properly to things, if you still have trouble i would set the idle. IF you cannot bring it to work, then continue diag.

Depending on things, your 94 may be obd 1.5 which has quite a few supported live data things and increased functionality since GM was pretty darn quick about ODB2 compliance they had a lot of the cars pretty close in 94 and 95, trucks may have been the same way
Need a tool that can dothat specifically if so

 

[Hoot Gibson]

Thanks AuroraGirl!

I already checked the IAC, and disconnected the battery to reset everything. I can't set the idle, because it won't idle. If I don't continuously work the throttle, the engine dies. Last observation is I have no fuel pressure, so now it's down to checking wires, then a fuel pump. Unless I'm misunderstanding something, that seems like the best way forward.

My OBD1 connector is a 12 pin, so I don't think I've got the hybrid OBD.

 

[PlayingWithTBI]

My OBD1 connector is a 12 pin, so I don't think I've got the hybrid OBD.

FWIU only some GM cars switched to 16 pin OBDI in 95. Trucks didn't switch until 96 OBDII.

 

[Hoot Gibson]

Thanks Peter, that makes my life easier. I'm reading so much differing info (other forums) my head hurts.

 

[AuroraGirl]

Thanks Peter, that makes my life easier. I'm reading so much differing info (other forums) my head hurts.

Your truck CAN idle if you have a helper or you turn the idle screw in. youre adjusting it anyway.

 

[Hoot Gibson]

Your truck CAN idle if you have a helper or you turn the idle screw in. youre adjusting it anyway.

Nope. Using the throttle it won't maintain a constant RPM. Not 1K, not 3K, not at any RPM. I have to constantly work the throttle to keep it running, or it dies.