I have an 89' IROC with a TPI 350. The car has 79,000 miles on it. At about 65,000 I replaced the engine with a short block from GM and edlebrock aluminum heads, crane cam, and a few other little things. It already had headers and a hi flow cat on it. I can't remember if it was right after replacing the motor or if it took a few weeks but the car would give me trouble idleing about every third time I'd start it. There did not seem to be any consistency to it. I talked to the guys at TPIS and they claim a chip would fix the problem. They burnt me a chip specific to my motor. Once I installed it I noticed a big difference and it seemed like the problem was fixed. But it's not, only it's actually pretty consistent now. The car always starts in the mornings or if it has been sitting for more than 8 hours. If I run if for a long time shut it down and come back a few hours later it won't stay runing unless I two step it. After 20-30min of continus driving it will finally idle by itself again.
The things that make me suspect the fuel pump is:
I am pretty sure it is original
It doesn't seem as loud as it once did
In my experience with electric engines worn ones don't work well hot but they can work if coaxed to. (could the suction from the motor coax the pump into operating again?)
The new chip is certainly giving it more fuel and I have the fuel pressure set to 55psi I think this could be killing the pump.

My only other thought is that the alternator has a hard time keeping up with the fans which run constently. Perhaps this has effected the pumps performance.

Please give my any thoughts or ideas. If I do need a new pump I'd like some suggestions please. Thanks for reading all of this.

Nick

 

You can hook up a pressure gage to check your pressure. If it is not within spec, replace it. The walbro units are about the best bang for the buck out there.

EDIT: By the way, welcome to the boards

 

I think it is too....55 psi sounds awfully high even on a modded motor. That'll just make your pump work harder than it needs to. Try backing pressure down to around 43-45 psi and monitor fuel pressure while driving and see what happens.

 

The extra fuel should go back into his return line without problem. Technically if he lowers the pressure than his pump will have to "work" harder. Fear not, your return line will relieve any pumping streeses.

 

In this system, it's a trade-off between pressure & flow: The higher the pressure, the less goes back to the tank, therefore there is less going through the pump. Higher resistance to flow causes the pump to "push" harder, making it draw more current, creating more heat; since it's cooled by flow, less flow means less cooling, while you're creating more heat. Not a good situation.

However, I'd bet you've got an electrical problem, such as ignition module.

(BTW, the engine doesn't "suck" fuel.)

 

The regulator is plumbed on the return side after fuel has reached the injectors....so it's basically a controlled restriction and bleeds off excess fuel depending on the spring pressure on the diaphragm.

High pressure=less volume (flow)....and vice versa.