Well, my uncle has an L98 vette that seems to have a bit of a problem. We attached a fuel pressure guage to the shrater (sp?) valve on the fuel rail and went for a drive so that I could be certain that the stumble was fuel related and not a problematic sensor somewhere. He says that he has replaced a number of fuel pumps and that hasn't solved the problem. As long as the tank is full, then the car runs fine. However, if there is a quarter of a tank or so in the car then it stumbles on turns or on full throttle as if the pump is being starved.

So, regardless of if the pump is replaced, the problem still persists. So is it possible that the pick up isn't getting to the bottom of the tank or is there another part that could be causing this problem.

Also, whenever you hit the gas the fuel pressure starts going all over the place. Is it possible that the regulator is causing all of this? Any help would be appreciated guy.

 

Define "the fuel pressure starts going all over the place". If its varing with throttle position over a range of 8psi or so, its normal - simply the fuel pressure regulator responding to changes in intake manifold vacuum. When you open the throttle quickly, pressure should rise to its maximum point, typically in the range of 42-45psi. As you shut the throttle quickly, pressure should drop, sometimes as much as 10psi on a full/sudden throttle closure at high rpm.

Sounds related to the pickup. But have you checked the FPR for leaks? Have you changed the fuel filter? Is he using a clean sock on the pickup for the new pumps? Is there any evidence of the fuel in the tank heating up, and causing vaporization of the fuel in the pump suction? Is the tank vent system working properly, preventing the tank from operating under high vacuum, which will also cause the fuel in the pump suction to vaporize? Is there loose wiring that might be losing contact when the car flexes entering a turn?

I'm assuming the engine is stock or near stock, and not modified to the extent that it needs a much larger than stock fuel pump to satisfy the injector requirements. And, just to be sure, is he buying the correct high pressure pump for a fuel injection system?

 

Thank you very much, Fred. We wound up replacing the fuel pump with a Walbro 255 LPH pump that we got from a local vendor, the hot rod barn. We also removed what appeared to be a diaphram that doubled as a coupler between the pump and the hardline and replaced it with a simple piece of hose. The car runs beautifully now and the pump cannot be heard, unlike the previous autozone or discount auto unit.

My uncle was very greatful to have his car back up and running again. He has been having this problem for a number of years and has been through at least 6 of the inferior units. Lifetime warrantee, lifetime of replacing them. You know how that goes.

Thanks again, Fred.

 

Very typical C4 fuel pickup problem. Go to a corvette forum and you'll find lots of threads on the subject.