Intermtent Starting and Killing problems - Third Generation F-Body Message Boards

AnonyMouse · 10-10-2009, 01:11 PM

Hello and thanks in advance for any help.
I have a 1991 Camaro RS 3.1L V6 MPFI, auto, all factory. It's my daily driver... or was my daily driver.

Some background stuff:
About a month ago, it started misfiring under load. It would idle fine, but when accelerating or climbing hills, it would miss badly. (The car was still driveable but, obviously, I didn't want to keep limping it around town.) I suspected it was the ignition coil, so I replaced that, but the problem persisted; it didn't get better or worse. So, I sent it to the shop for a diagnostic and they told me my #4 injector wasn't firing under load. I replaced it and all was fine... for a little while.

I drove the car for a week, with no problems, then one day, it randomly killed. I was driving along fine when it shut off without warning. But, it started right back and I was able to get it home. I did some reading and everything told me it was probably the fuel relay, so I replaced that got rolling again. Everything seemed okay, until later that same day it shut off again. I started it up and tried to get it home, but it shut off again... and again... and again. It always started, but would never stay alive. Sometimes I'd get it to move a few feet before it killed, sometimes it would make it miles before it killed. I eventually called in the tow truck and it is now resting on my driveway.

So, the verdict:
It starts every time, without any difficulty, but what I get after that seems very random. Sometimes it will run as if nothing is wrong; under those circumstances I could drive it, but there's no telling when it will kill again. Other times, it will idle low after starting and won't respond to accelerator inputs; when it's in one of those moods, I can put the accelerator all the way to the floor and it will not make a difference. Sometimes it will run like that for many minutes and other times it will sputter and die within seconds of starting.

I'm all out of ideas. I believe it's a fuel problem, but I'm reluctant to replace the pump until I'm sure. Dropping the tank to get at that thing is a nightmare, so I want a second (and third, and fourth, and...) opinion before I go at it. The pump never fails to prime when the key is in the 'on' position, which leads me to beleive it may not be at fault. And the car usually runs more than a few seconds, suggesting it is getting gas until 'something' decides to shut off the flow.

Any help would be appreciated. I don't even know where to begin.

PS: I just realized there's a typo in the thread title. Sorry about that.

AnonyMouse · 10-10-2009, 04:39 PM

UPDATE:
I just bought a pressure tester kit and checked my fuel pressure. 41 psi when primed, about 36-38 when running. Then it leaps to about 44psi when it starts idling bad.

Now, I'm even more clueless than I was before.