PontiacBonnevilleClub.com

The car is not my SSEi, it's a friend's 1994 naturally aspirated Bonneville. Driving down the road it runs good, briefly, then starts surging, won't accelerate, slows down, won't climb hills, and eventually will stop altogether. At a standstill (no load), it idles well, but when revved up (again, no load) it almost hits 4000 rpm when revs drop severely then climb back up, repeat, etc. (surging, with the foot steady on the throttle). It has 38psi fuel pressure at idle, drops to 20psi when revved and the rpms drop--eventually dropping as low as 5psi or so as it stumbles down--all this with the foot at one position on the gas pedal. I don't know if the surging is caused by the fuel pressure drop or if the surging causes the fuel pressure drop, but it seems to me that fuel pressure should be more or less constant, with only slight drops on increased revs. What we've done: since lots of problems are ignition related, we replaced the ignition module with a known good unit. Didn't help. We Ohmed out the coil packs and they looked good, but that doesn't always mean they ARE good, so we replaced two of the three coil packs with two known good units (I have three coil packs but one is known bad). No change. I hooked up my scan tool and noted TPS is good (reads from 2.67 to 99.6% as appropriate), and O2 was sorta questionable--didn't seem as active as it should, but didn't throw any codes. In fact, no codes anywhere. Mass Air Flow went up and down as expected...
My first inclination is to go with a fuel problem and start troubleshooting that, from the fuel sock to the injectors. Unfortunately my experience is with forced air cars (Pontiac SSEi and Turbo Buick) and their fuel pressure goes UP with RPM and boost. How does the fuel pressure react with an NA car? I'm pretty sure it shouldn't drop as drastically as it does!
Any help appreciated.
Keith Hansen
1994 Bonneville SSEi

If the car has over 100k miles...it could be just the fuel pump dying.

Also, how old is the fuel filter in the car? If that is clogging, it will be cutting pressure as flow rates rise.

The base number for pressure already seems too low. I'd definitely vote for the fuel pump and filter being changed.

Is there no SES light? If there isn't, that would support this diagnosis, if there is, then please give us the code.

wjcollier07 wrote:If the car has over 100k miles...it could be just the fuel pump dying.

Also, how old is the fuel filter in the car? If that is clogging, it will be cutting pressure as flow rates rise.

The base number for pressure already seems too low. I'd definitely vote for the fuel pump and filter being changed.

Is there no SES light? If there isn't, that would support this diagnosis, if there is, then please give us the code.

Either the fuel pump is dead or the filter's clogged, or both. The fuel injectors need 3 bar at the rail to spray correctly. 5 PSI? It's toast.