[RoopertTheGMkid]

I have been working very hard to get this car running, Shes a 94 with a 4.3 L99 V8, I've put in a new Sentra fuel pump that's getting low PSI, like piss poor pressure. The engine runs perfect when I pour fuel down the intake, it just won't get enough to run on it's own from the tank. If anybody could help me identify what's going on I'd greatly appreciate it.

 

[jayoldschool]

What's the actual measured fuel pressure number? Key on, then cranking, then running. "Piss poor" is a wide range, lol

 

[RoopertTheGMkid]

What's the actual measured fuel pressure number? Key on, then cranking, then running. "Piss poor" is a wide range, lol

I mean it just barely leaks out of the fuel filter when unhooked. It shoots out maybe 2 inches before drooping and hitting the ground, I'm not very well off so I don't have the right tools to measure it.

 

[Fix Until Broke]

That is an indication of flow, not pressure.

 

[Podor]

There are so many different variables. The pump should kick on for 2 seconds when you turn the key on or continuois while cranking. You should be able to hear the pump run if you're right next to the tank or through the filler neck. If you don't hear the pump, it may also be an electrical issue. If you're checking after the filter, you could have a restricted filter. Also, if it runs when you add fuel, it may be an issue firing the injectors.

You may be able to rent a fuel pressure guage from your local parts store, like Autozone. Start there. I totally understand not having the tools and being on a budget, but throwing parts at it will cost a ton as well. Properly diagnosing will save money and time.

 

[sherlock9c1]

You may be able to rent a fuel pressure guage from your local parts store, like Autozone. Start there. I totally understand not having the tools and being on a budget, but throwing parts at it will cost a ton as well. Properly diagnosing will save money and time.

It's expensive to be poor. Think strategically, get a better job, get rid of people and things that suck money and energy from you. You are better.

There was a run of bad sending units for awhile - the hose between the bulkhead and pump was not rated for pressure and will burst within a few hundred miles of driving. If it's a corrugated plastic hose, it's good. If it's black rubber curly-Q hose, it will fail. I think it was limited to the Delco/Delphi sending units but Spectra might have been affected as well. Do you have any pictures of the sending unit before you installed it?

 

[RoopertTheGMkid]

I think I may have narrowed it down a little, sorry for being inactive, life is busywork for a farmboy, anyhow this mess will be sorted out soon, when the weather lets up I'll dig deeper. Thanks for those who posted!

 

[SAH62]

Broken knock sensor wiring connector? I don't know if that'll cause a "no start" condition, but you definitely want to fix it. Replacements (you'll need to cut the wire and solder in the replacement) can be found inexpensively: 1995 CHEVROLET IMPALA 5.7L V8 Knock / Detonation Sensor Connector | RockAuto

 

[Podor]

The purple O2 sensor wire looks suspect as well. Almost looks like it melted. That whole harness may have issues.

 

[jayoldschool]

I'll say bravo for the well-lit, in focus picture! This is a lot better than we usually get, lol

 

[Z09B4U]

Is the third sensor (on the oil pan) not the infamous low oil sensor with the fuel pump bypass switch?

If the car has not been run in a while you might try powering the prime/pump relay bypass wire. Maybe constant fuel supply(pressure) will get it running the first time

To use the prime wire you need a 15 Amp FUSED 12 volt source. A old transformer type 10 amp charger(it should have a internal breaker) might get it going but a "smart" charger will not.

 

[RoopertTheGMkid]

I'll say bravo for the well-lit, in focus picture! This is a lot better than we usually get, lol

Thanks! Had the hood open on a clear day, the car is outside right now.