Fuel pressure sensor install question/bad fuel pump?

[rob249]

Truck is a 1994 GMC Yukon 4x4, picked it up about this time last year. As summer came, it started vapor-locking in traffic and to diagnose the problem, i installed a mechanical fuel pressure gauge. The gauge is screwed into a brass tee fitting with a male thread on one end going into the throttle body, and a female that the fuel line screws into on the other. The gauge was reading 9 psi, which indicated a weak fuel pump(11 psi is spec). My sender also stopped working, so I put a whole new pump/sender assembly(delphi) in the tank.

After the new pump, i was reading 11psi, and no vapor-locking, no issues whatsoever, for about 6 months. About a month ago, i was on the freeway, going east out of town, which is uphill. I had immediate power loss and backfiring, once i slowed to 45mph, it ran fine. Any attempt to accelerate past 45mph was met with the same. Going west is flat and i can run 80mph all day with no issues. I also experienced this same thing going up a mountain, about halfway up, no issues going back down. Im still running about 10.5 psi on the gauge at idle, but i cannot see the mechanical gauge while driving when i have the issues, So i picked up an electronic gauge i can mount inside the truck. Its a Glowshift tinted series, with an electronic sender.

Am i right to think this new fuel pump is already going bad?

There really isn't any room for the sender on that tee due to the air-cleaner. Could i just use a threaded nipple off the tee and another on the other end screwed into the sender. Then i could mount the sensor remotely, im just worried that the hose will just trap air and prevent fuel pressure from reaching the sensor, or will the fuel just displace the air to the return line? Any thoughts are appreciated, thank you.

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[Lanny]

If you could bleed the line then I wouldn't see any issues. After the system shuts off air doesn't really rush down into it. Id put the sender on with the long hose and give it a shot. Worst you can get is a bad reading at idle. And since you already know what your idle pressure is, you should know if this new gauge is reading it wrong or not.

 

[rob249]

So it did work, and I am running low fuel pressure under load. Around 10.5-11psi at idle, then it slowly drops while under load, to 8.5 psi before it starts backfiring and lugging. Beware Delphi fuel pumps.

 

[someotherguy]

Any OEM application fuel pump you get now is gonna be China junk outsourced to a manufacturer that does what is called "customer pack" where they put their product in your branded box. With Delphi or AC Delco at least you have the chance that their QC might be a tiny bit better than the no-name junk. If you want guaranteed garbage, buy an Airtex. I'll keep buying AC Delco and Delphi.

BTW you don't see vapor locking with a return-style fuel system as the fuel is constantly circulating. Vapor lock is a carbureted-days issue..

I'll agree with you though 8.5 psi is definitely too low. Spec is 9~13 and I wouldn't be happy with anything less than 10~11, really.

Richard

 

[rob249]

I thought vapor lock was a thing of the past also, but my truck was definitely doing it on the old fuel pump. The symptoms of the new pump going bad are just similar to vapor lock, only way i could describe it. I've also seen in a few forums that the delco's are just re-boxed delphi's, dont know if that's true. I think Im going with a Bosch pump.

 

[someotherguy]

Vapor lock and insufficient fuel delivery are not the same thing. When asking people to help troubleshoot long distance, terminology matters.

Richard