basically i just put a brand new walbro high pressure fuel pump in my 1991 z. after i put the pump in the car has a hard time starting unless i give it gas (like its not getting any fuel, it will just keep turning over). now after i went to the track i realized my car is cutting out (most notably at approx 80mph, 4500rpm, 3rd gear). it hesitates extremly badly but only when pushing the car hard.

anyone have any suggestions on whats wrong here?

TIA!

 

Sounds like a fuel delivery problem.

What's the FP WHILE IT'S DOING IT? (not while it's sitting idling...)

 

im 99% sure it has to do with the new pump but i just dont undertand what could be causing it. and i dont have a fuel pressure gauge to test that unfortunatly...

 

Sounds like, it's time for a trip to AutoZone for a gauge.... one of the most fundamental pieces of test equipment for working on fuel injection. You'll get your money's worth out of it, sooner or later; maybe right now.

 

It sounds more like a ground problem to the pump. You probably have a high resistance ground wire and it's starving the pump for voltage.

I had to silver-solder my ground wires throughout the sending unit because GM used a spot-weld as a ground path. Perhaps yours is the same way?
A little work hardening and the resistance will go sky-high. It only takes an ohm or two to K.O. your pump, which has only one or two ohms in its own windings. Add one ohm of resistance to your ground path and you lose 33% of your current.

--drb

 

i thought it might have to do with the wiring, putting more demands on the old wire might actually cause a problem that wouldnt show up with the factory pump's demands.

but i still didnt get the part about it not starting like it should, i can understand at WOT but not when starting

 

Like the others said, perhaps it is time to invest in a fuel pressure guage. When you first key on the ignition, the pump is supposed to engage for a second or two in order to pressurize the fuel rail. Fuel pressure is supposed to be in the neighborhood of 45 PSI.

Have you adjusted the fuel rail pressure at all? If so, then maybe you have exceeded 60 PSI and you are hydraulically locking up the fuel injectors. That's a bad, bad thing and will make the engine lean out under power.

Try this first: Get yourself a pressure gage and a multimeter.

1) Check fuel pressure at key-up and at idle. It should be around 45 PSI in both cases with the pressure regulator disconnected from manifold vacuum.

2) Get under the car and check pump voltage at the connector. It should be at least 12.5 volts at all times

3) Check the pump resistance by unplugging the connector at the fuel tank and probing the pump: With the pump and the series resistance of the wiring harness, the series resistance should be no more than two ohms. 12.5 V / 7 AMP = 1.75 OHMS

If you key up the car and pressure spikes, then drops rapidly, it means one of two things: Either you have a leaking injector or else you have a bad check valve inside the fuel pump.

Hope this helps,

--Dan

 

very good info. now that i think about it the metal end cap on the pump nipple (the check valve) fell off wheni was installing the pump. i put it back on and it was secured inside the rubber fuel hose but that could possibly be my problem.......damn