[00 SS]

My daily driver is an 88 Buick Park Ave. Lately, I've been having trouble with it running right when the engine is hot and I restart it. Almost seems to be vapor locking, but it's multiport fuel injection. Ocationally when this happens, I can bleed some "air" or maybe fuel vapor out of the schrader valve on the rail which sometimes helps, sometimes not. It starts, then idles like it's missing badly and the engine won't rev up. So far, I've been able to coax it into working and getting me where I need to go, but I at a bit of a loss as to why this is happening all of a sudden (the last week or so). The weather hasn't been too bad lately and it was certainly hotter earlier in the summer and it ran fine. It seems OK while I'm driving and after it's been allowed to cool down all the way.

The recent maintenance includes:
new fuel filter
new plugs
new coil packs and igniton contol module
Removed and cleaned injectors (really were pretty clean to begin with)

My ideas:
fuel pump is low on pressure allowing the fuel to vaporize in the rail while sitting after driving
Bad presure regulator not holding the pressure up while sitting after driving, or sticking not allowing the vapor to exit and return to the tank.

Any insight or ideads would be appreciated.

[00 SS]

Thanks guys. I ran the tests above.

Test 1. Pump runs for about 1 second and pressure comes up to about 30 psi.
Test 2. Pressure is steady, watched for about 5 minutes.
Test 3. Car starts and pressure is about 38-39 psi.
Test 4. Vaccum line is dry. Pressure comes up to 42-43 psi but the needle on the gauge is not steady, it seems to pulse rapidly in a 1-2 psi range.

Extra test. With the gauge in place, everything connected normally, and engine running, working the throttle induces a momentary pressure increase to about 42-43 psi. Loss of vaccum causes the regulator to increase pressure.

From the tests above, I think I can rule out a bad regulator. The pump might be going since the initial (key on engine off) pressure is below spec (40-43 psi according to my book). But that could also be the result of the run signal interval being so short. The book I have says it should run for about 2 seconds. It does not run that long. However, cycling the key off and on again does not result in much higher pressure. About 33 psi.

The 38-39 psi at engine running seems about right to me. How can the pump do that if it can only make 30-33 psi with the engine off? It seems that the pump may be going, but it may also be the pump controls.

Any ideas on which it may be? I'd hate to go through the ordeal and expense of replacing the pump and have it still not work and have the real problem be some stupid relay or something.

This post has been edited by 00 SS: Aug 16 2011, 06:20 PM

[CrashTestDummy]

Thanks guys. I ran the tests above.

Test 1. Pump runs for about 1 second and pressure comes up to about 30 psi.
<SNIP>

The 38-39 psi at engine running seems about right to me. How can the pump do that if it can only make 30-33 psi with the engine off? It seems that the pump may be going, but it may also be the pump controls.

Any ideas on which it may be? I'd hate to go through the ordeal and expense of replacing the pump and have it still not work and have the real problem be some stupid relay or something.

The lack of initial pressure may be because it's not spinning up long enough. I'm at a loss why that is, but it would seem to me 1-sec prime-time would be a little short. I'd verify your battery cables and engine/chassis grounds are all clean and tight. Perhaps there's some excessive voltage drop at key-on, making the system think the pump has run enough at prime. I do know the OEMs are notorious for wiring a lot of circuits with way too small a gauge of wire to run the accessory they are supposed to. There are a LOT of GMs out there that see a performance gain from running larger-gauge power wires to the pumps. The pump seems to last a bit longer, too.

If the thing uses a relay, I'd check/replace that. It can't be too expensive, and should certainly be easier to replace than a pump. Perhaps try this after running the wires and cables.

And just another thought: The fuel system in our 92 B4C Camaro involves the oil pressure switch. I got out of the car one day only to hear the fuel pump continuing to run with me holding the key in my hand. I popped the hood, started wiggling wires. There was a harness that went down to the oil filter/oil pressure switch area, and the pump quit. That was the last I had of that problem. If yours has such a pressure switch, perhaps it can be part of the problem somehow? Yeah, I'm grabbing at straws here.