1995 Pontiac Grand Prix runs rough

AARON701

MEMBER
1995 PONTIAC GRAND PRIX
6 CYL
FWD
AUTOMATIC
167,000 MILES

1995 pontiac grand prix se 167000 miles 3.1 3100 V6 engine. Car started running rough, idles rough starts but runs very rough like a possible cylinder misfire but unsure. No check engine light on so difficult to diagnose. Seems to be a strong fuel odor coming from engine when you start it, from rear of engine. Pulled the plugs cylinder 4 plug seemed wet with fuel. Replaced plugs with new ac delco and plug wires still runs rough. Checked for vacuum leaks and tried replacing fuel vapor canister solenoid. Still runs rough. Tried replacing EGR valve did not help then tried replacing complete coil pack and ignition module with a replacement from a auto salvage place. Still runs rough. I am puzzled got any ideas?

2 Replies

ERNEST CLARK

MECHANIC
1,730 POSTS

Since you've changed your ignition system, you can rule that out as a possible cause (Assuming your junk yard parts work).

The next thing to check is fuel. Though I can't be 100% sure, your issue sounds like a leaking fuel pressure regulator or one/more fuel injectors.

Pull the vacuum line that leads to the FPR and smell/look for fuel. If there's ANY at all, then replace that.

If that checks out, hook up a fuel pressure gauge and check system pressure with "Key on/Engine off". You pressure should hold steady. If not, pinch off the return line from the FPR and turn of key, then back on (engine off). If pressure continues to fall, then you have a leaking injector. If it stops falling, you have a leaking FPR.