Intermittent 0303 and 0171 code
 

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.

he said he swapped wires, but going back through dont see where you swapped coils?

Shame on me for not noticing. :eek:

Swapped the coils also. Same problem. Cleaned the ICM. Same problem. New plug in #3.

Part that is difficult for me to understand is does not set a code when it doesn't start.

Diagnostics won't start until the PCM sees the engine running for X seconds/minutes before it starts testing.

check fuel pressure, swap injectors?

I have the exact same problem on my 2000 Bonneville po171 and po306 sometimes po171 and other times just two po306 codes so I'm watching this thread for answers....

I put some heet in my tank and seems to have done the job...

Check the iac sensor ....

Guys,

I found it. It was the fuel pump. I put in a new Delphi and a strainer about 1.5 weeks ago and everything seems is running fine.

I thought I had enough fuel pressure because I was getting soaked when I checked manually. When I put a loaner gauge on from Autozone on it I only had 35 lbs. Specs say 48-55lbs.

Along the way I have cleaned the ICM, IAC, throttle body, EGR valve, TPS. I have replaced MAF, O2 sensor, EGR valve gasket, throttle body mounting gasket and #3 injector. I checked for vacuum leaks.

Shows me that you always need the right tool for the job!!!

Many thanks to all for the help,

John

I think you owe Justin a prop. He nailed this one.