What would cause my 1997 Pontiac Sunfire SE 2.4L 4T40E to stall when...

[mr. bojangles]

...stopping or turning? I rented a code scanner from AutoZone, and first got a random/multiple cylinder misfire code, then I cleared the light. As the CEL kept coming back on, I continued pulling codes and resetting them each time. I got a misfire code for, I believe, each cylinder -- at different times (one time it was cylinder 3, one time it was cylinder 2, etc.). So it appears that any cylinder misfires at any time it so pleases. I tried swapping the entire coil pack/cover/housing (no cracks)/spark plug boot assembly from another vehicle, and the same problems persist. Last year I replaced the AC Delco plugs with Autolites (preventive maintenance), and I have read time and again to only use AC Delco plugs, but I was short on money at the time, and the car has ran fine until now. It would seem awful coincidental for all plugs to go bad at the same time; they appear to have normal wear and I double-checked that they are still gapped properly. The car will only stumble when coming to a stop/slowing down to turn a corner, at which point the flashing CEL comes on. If I just stop, the car dies. If I put it in neutral and continue to give it gas for a short bit, the "loping" idle will smooth itself out to normal, and I can continue driving, but only until I approach another stop or turn. The timing set was recently replaced (preventive maintenance), and the car ran great, so I have ruled out the timing being off. The head gasket is new, as are most seals. There are no leaks of any kind. The fuel pump and fuel filter are also relatively new. I am leaning toward injectors or possibly an O2 sensor, but I honestly don't know for sure; this problem really has me stumped. Thanks again to you guys for reading and for any advice you may give!!

 

[Frankie]

Have a fuel pressure test done. Sounds like the fuel pressure regulator may be bad. +

See if any of these symptoms look familiar.
Fuel Pressure Regulator Failure Symptoms:
Engine runs rough
Engine stumbles or sputters
Engine runs very rich - black smoke from the exhaust
Engine will not start
Engine starts but stalls shortly after startup
Noisy fuel pump
Noticeable decrease in fuel mileage

Hope this helps and good luck

 

[REV B]

Random misfire caused by a loss of spark or a weak spark may be due to fouled spark plugs, plug gap too wide, bad plug wire, weak ignition coil, cracks or carbon tracks in an ignition coil or rotor. Remove and inspect the spark plugs. If oil or carbon fouled, the engine is probably sucking oil past worn valve guides and seals. Replacing the spark plug will only temporarily solve the misfire problem. If the spark plug is normal, check the plug wire and boot for damage or looseness. Measure resistance end to end. Replace the wire if resistance exceeds specifications (about 50,000 ohms/foot). If the spark plug wire is loose, damaged, burned, chaffed or exceeds resistance specifications, replace it. On coil-on-plug (COP) ignition systems, there is no spark plug wire so inspect the coil sheath for cracks or carbon tracks. If ignition and compression are both okay, focus next on the injectors. Use a test light or voltmeter to see if the injector is receiving voltage when the key is on, and that the injector solenoid clicks when the injector circuit is grounded. If the injector is functioning electrically, it may be clogged with fuel varnish deposits. If cleaning cannot restore normal fuel delivery, the injector must be replaced.