I have a 97 Bonneville NA with about 198k. About 109k on a new engine. Replaced UIM and LIM for the 2nd time about 1000 miles ago. Seemed to solve 0171 code that was showing up. After that I have been getting a 0303 code on a repeatable basis with the following conditions. Engine starts fine in the morning. Drive about 30 minutes then stop for 30 minutes. Restarts fine runs about 15 seconds and check engine light begins to flash. Definitely runs rough as if it has a misfire. Run about 2 minutes and everything seems fine. Scan indicates 0303 code. Indicates that there are 2 occurrences. Have been monitoring in closely the last few trips and it has also been intermittently setting a 0171 code although check engine light has been illuminated.

I need help. Any ideas?

Thanks,

John

The P0303 code is a misfire cylinder 3. Start with pulling that plug and inspecting it. My be fowled or cracked. Check for any oil build up in that area. Inspect the wire for the cylinder as well. Read this for the P0171 code. https://www.gmforum.com/showthread.p...36#post1390823

Thanks for the info. New plugs went in when I changed UIM and LIM. Rechecked since the 0303 has shown up and everything looks fine. Wires were new about a year ago. The repeatablity is what has me baffled.

John

start swaping things and going back toward the icm. change the wire with another to see if the code moves to the other cyl. if not move the coils. somethings to look for are corrosion on the wire ends, coil terminals and the tabs that stick out of the icm

Guys,

I need help here. The problem has expanded. No problem starting the car cold running 20 minutes and restarting within 2 minutes of turning the car off. If however I let the car sit about 15 minutes it will start and run rough and I need to "feather" the pedal to keep it running. RPMs jump up and then settle back to about 600. This will set a 0171 and 0303 could typically. If I run it for 20 minutes and then let it sit 30-45 minutes it will try to start and run rough and no amount of feathering of the pedal will keep it running. I have to let it sit about another 10 minutes and then it starts and runs fine.

I an totally confused. I have swapped wires, checked modules, checked vacuum lines, cleaned TPS, replaced MAF, replace 02 sensor.

At a loss. Any suggestions on what to try next?

Thanks for the help,

John

check fuel pressure. whens the last time the fuel filter was replaced?

Swapped the fuel filter right after this started. Don't have exact value for fuel pressure but when I depress the valve on the rail I have significant amount of fuel coming out.

When it sprays you in the eyes, thats when you know you have pressure!!

as scientific as that is these engines dont run right if they dont have the right pressure and have a tendency to decrease the pressure when the pump isstarting to wear out or if the electrical connections are getting corroded. or if the fpr is going bad.

For the P0303, take the #3 spark plug and swap it with #5 and see if the misfire follows it. If no change, swap the spark plug wire the same way.