RudyInTheSkies

The PCM threw a code of P0303 - Random Misfire Cylinder #3. In an effort to solve the problem, I swapped #3 plug and #3 coil with other cylinders in an effort to transfer the condition to determine if one of the components was faulty. 286 miles later, another P0303 code was thrown, proving that neither the plug nor the coil was the culprit. Then, I learned the unhappy news that this code is also thrown when there is a valve or valve seat problem existing. Only thing is, the car starts and runs like a champ, with smooth power, idle, acceleration with no loss in fuel economy. No symptoms of deeper engine trouble. I would appreciate any and all assistance I can get to work through this. Thanks!

donbrew

You need to start with a cylinder compression test and a leakdown test. Those will tell you how bad the news is.

Does coolant disappear?

RudyInTheSkies

No. That is what is so annoying. There is nothing whatever to suggest a problem. I will however, have a compression test and leak down test. If anything else occurs, don't hesitate to let me in on it! Thanks!

donbrew

You have already done the easy testing.

Oldblue

Best of luck, if the leak down and compression test don't show any deep engine issues, disconnect the battery for 30 minutes to reset the ECM and BCM , all will be cleared, and this should resolve the issue, also double check the connections to the coil pack and injectors! Just as a precaution

RudyInTheSkies

Thanks for your response. The compression readings were #1-190 #2-190 #3-170 #4-190. While #3 was lowest, I believe the reading is high enough to preclude a leak down test. Correct me if I am wrong, though. I have reset the PCM and BCM as suggested. As a further precaution, I have everything crossed, i.e. fingers, legs, eyes, etc. so now we'll see!

whopper

That #3 is starting downward. Seems it is always cyl #3 that is causing problems.

I'd suggest a leak down test. It won't get any better, and even if it isn't worthwhile doing an expensive fix yet, you need to know what is causing the problem so you are prepared in the future.

RudyInTheSkies

Thank you for your input. I have arranged to speak with a tech at GM about this problem. You can bet your last dollar I will be addressing the issue of design fault and see if I can get any satisfaction from the General. There is just too much of this for him to fob me off. They probably have a complaint file as thick as a New York City phone book. When I get the skinny on this problem, I will post my findings. Watch this space! Thanks to everyone for their help thus far.

whopper

Best of luck - and do keep us posted. :)

Snoopy

This is one of the funniest posts I have read.

You have about 10% difference from one cylinder and it's a design flaw? And you haven't even established IF that is your "coding" problem.

I'll wait to see your results.