3800Impala

My 2000 Impala LS with the 3800 has a fuel pressure problem. Been there since June, when I got the car running. (Bought in January, worked on all winter.) The car runs great, engine runs really smooth. Except occasionally, whether engine hot or cold, the cranking time is WAY too long. Sometimes takes a second try to start. Got a fuel pressure gauge a few days ago. As soon as the car gets shut off, pressure drops. While running, I'm getting 37 PSI @ idle. Car has terrible MPG, about 13 HWY. Things I've tried:

Replacing fuel pressure regulator
Replacing O-rings on fuel injectors last Thursday (stopped the leak for a few hours)
Removed FPR and reseated last Friday (also stopped the leak for a few hours)

But the problem just keeps returning, although so far, despite the pressure drop, the hard start has improved since replacing the o rings. Any help is greatly appreciated.

Frank3

3800Impala, I don't have my manual here with me right now so I'm going entire from memory so I may get a thing or two wrong, but I think 37 PSI fuel pressure while running is too low. While it may run, the fuel is probably coming out of the injectors like a spray out of a kids squirt gun rather than a fine spray. This could be caused by several problems. If you put a pressure gauge on the fuel rail, monitor the gauge, then turn the key to the ON position - NOT START position. The fuel pump is supposed to be turned on for a second or two to pressurize the fuel system/rail. If this is not happening, then the only way to turn the fuel pump after that initial pressurization is through cranking the engine over UNTIL it builds up some oil pressure, At this point, I believe the oil pressure sending unit is supposed to provide power to energize the fuel pump circuit/relay. Which could explain the long cranking. As for the fuel pressure, it could be either a bad replacement FPR, a bad fuel check valve (in the pump?) or a leaking fuel injector. Just thinking of it now, how is the fuel filter and when was it replaced last? I would start there first if it hasn't been touched.

3800Impala

I can hear the fuel pump when I turn the key on (engine off). Starting at 0, pressure build to about 37 after two key cycles. I thought 37 was too low, also. Other people claim to have pressures around 45-50. I replaced the fuel filter with an ACDelco one (as well as all the other filters) 1200 miles ago. The fpr was also an ACDelco.

3800Impala

I'm thinking it probably IS the fuel pump getting weak, but I don't want to replace it if it's something else. What do you think?

Frank3

The pumpcould be getting weak, but with the pressure on the rail dropping to 0 as soon as you shut it down makes me thing you have something else leaking the pressure off somewhere.

3800Impala

I need a new o ring for my fuel gauge (it already broke ), so I won't be able to check it for a few days. Both lines have been patched with a few inches of neoprene tubing. If I pinch the return line and check the pressure, will it help determine if the FPR is the cause? If the fuel rail was leaking, would I see gas? I haven't seen or smelled any gas. Now that I think about it, even though I cant see or smell a leak, and it seems tightly put together, could it be the neoprene line leaking?

tech2

after you get your fuel pressure gauge fixed...and if there still is a fuel pressure leakdown. you should isolate the source of the leak.




prime the system and clamp off the supply. if the pressure drops, the leak is the regulator or injectors. repeat on the return side; prime and clamp off the return side...




do not pinch off plastic fuel lines...find a rubber section. I made up fuel line hoses with shut off valves that quick connect onto the existing lines for this purpose.


typically, leakdown on the supply side cause a long crank that can be ID'ed by cycling the key to prime the supply line...then it will start normally.


injector or fpr leakdown will cause a flood condition that occurs on a restart after a hot soak. Starting in clear flood mode would ID this concern.

3800Impala

Ok, I was able to just exchange the whole gauge and got a new one. Just checked it and the pressure is 38 psi, key on engine off. Engine on & idle pressure is 36. If I rev it, the pressure goes up to about 38. Now the pressure drops VERY VERY slowly, like 1 psi/min or less. Hard start seems to be gone. How long should it hold pressure? I pinched a rubber section on the return, pressure still drops VERY SLOWLY. I pulled off the return completely, no fuel, pressure didn't change rate it drops.

Edit again: Now the pressure has stabilized at 37 psi for now. (key off), been like that for several minutes.

tech2

if it hasn't dropped in 5-10 minutes your ok.



if it does drop with the feed and return blocked off...the only leak points are the injectors or fpr into the vacuum hose from the intake.

3800Impala

Ok, I tried a new pump. Nothing changed. I've looked into everything.
The only thing is the fuel line AFTER the fuel filter (towards the engine) is extremely rusty. The line has "rust bubbles on it. I cannot see or smell a leak, though (and it feels dry). Something is just not right. I'm getting 12 MPG Hwy. I'm not getting any codes. (Although, a couple hundred miles ago I got the downstream O2 code, but then it cleared itself.) If I remember correctly, the fuel trims were close to 0, too.

1400 miles ago:
New plugs/wires
New air filter
New Fuel Filter
Oil change
New FPR
100 miles ago:
New fuel injector o-rings
Today:
New fuel pump