5.7-89GTA

I've had this car 4 years. It is stock and ran well until recently. I am trying to hopefully get pointed in the right direction. Here is the problem:

Recently it has taken 3,4 or 5 attempts to start the car. Seems to be "missing", but eventually clears up, but surges occasionally or acts like it wants to stall. The SES light has not come on, but it works. At one point (at a car show no less) it started up, sounded like it was running on 2 cylinders, stalled and would not re-start for 15 minutes. Then it started and ran seemingly normal back home.

What I have done so far:

Replaced fuel filter
Replaced the oval shaped relays on driver's side. I think one is the MAF, the other I am not sure. Did not replace fuel pump relay.
Checked fuel injectors - 16.7 ohms all 8. They appear to be original.
TPS .51 VDC at idle.
Fuel pressure: is at zero after sitting a few hours. With key on I can hear pump (it is not loud). Key on psi is 11-12. Start car, takes a few tries. Car stumbles at first idle. As fuel pressure comes up it smoothes out. Fuel pressure tops out at 31-32 psi. Same with gas cap on or off. Shut car off pressure rises to 38 psi, then slowly bleeds down in a few hours.
3 summers ago I replaced cap, rotor, coil and plugs. Wire "look" ok, but seems like a fuel problem.

I am thinking fuel pump or regulator. Most information tends to indicate the pump would just fail, not deteriorate slowly. I do not detect any vacuum leaks to the regulator.

Any input appreciated. Thank you.

91zl98

sounds like a pump thats low pressure on the prime. It could be the cruddy pulsator the put on top of the pump leaking those belong in the garbage.

Zig

Do you have any fuel leaks? Check front to back and around the fuel rails/injectors. Fuel pressure should jump to 40psi or greater during the prime. If it's not, that's a problem. Sounds like a weak pump. Slow to prime and then slow to build pressure.

You can remove the fuel pump relay and jump power to the pump and see how long it takes to come up to max pressure. It should get there in about a second.

Agree with 91zl98 on the pulsator but you have to drop the tank to get to it and if you are already there, replace the pump.

5.7-89GTA

Thanks for the info, I am resigned to the fact that I will probably have to replace the pump. The car will remain stock, or only slightly modified. Pump recommendations? Reliability is the prime concern.

There are no leaks detected.

Thanks

Zig

I just put a Racetronix (Walbro) pump and Hotwire kit in mine a couple weeks ago.

5.7-89GTA

Problem was fuel pump. Car would still run, but crappy. Bought a FP gauge, 11 psi at key on and would rise slowly to 32 psi when running. Then bleed down to zero when shut off for a couple hours.

This past weekend replaced pump with a Bosch unit from rockauto.com. Was not a fun job, but got it done. Car now runs well and has a healthy idle. Key on psi is instantly 42 psi, idle is around 38 psi and with vacuum pulled from FPR 45 psi.

Most pump issues I have read about involved the pump dying flat out and the cars would not run at all. Mine died a slow death, the first symptoms being difficulty starting because the fuel pressure had leaked down and the pump was slow to build pressure. When there was barely adequate pressure to run it would start and slowly run slightly better as the pressure reached 32 psi. My car had around 67,500 miles when the issue first arose. Appears to have been the original stock pump that I replaced, the tank appears to have not been previously removed.

TTOP350

iTrader: (8)

Did you install a new fuel filter also??

5.7-89GTA

Yes, new filter, strainer, pump relay, GM tank o-ring. I did not know about that stupid pulsator thing until too late, but I replaced the rubber fittings in it. I wish I had replaced it with the hose and clamps.