I have a 07 with 2.4. CEL came on today, cyl 3 misfire. I just replaced plugs and air filter on Friday. The car has 167K. Any suggestions. Thanks.

 

I would start by changing the # 3 coil pack with a different cyl. And see if your problem moves to a different cyl. If the problem stays on the same cyl. Then swap the spark plug and see if the problem moves to a different cyl.

After the swaps if the misfire is still on number #3 then it's time for a compression test.

 

and double check the coil pack connection

 

I might add......

If you are saying, "......just replaced....." and you mean you replaced the items stated and started the car JUST AFTER the install (or maybe an hour or so later), then you did something wrong. Look closely at plug # 3 and see if you perhaps broke the Iridium tip....it is VERY small and breaks easily if you tried to gap the plugs....which you shouldn't do.....they are pre-gapped. Also check the coil pack and assure it is installed securely....to the plug and the wires to the coil. You may have, inadvertently, wiggled a wire lose, as suggested by previous posts.

 

Thanks for the quick answers. I will have to give it a try. Any possibility it could be the injectors?

 

Yes it could be an injector. There are a lot of things that could cause a misfire so you have to go through the process of elimination to find the cause. As other has suggested a good place to start is where recent work was done first. Mistakes do happen.

 

The gap was not touched. The plugs were taken right from the box and installed. They were AC Delco iridium.

 

I have seen damaged spark plugs right out of the box before. Al it takes is for someone to drop them in shipping or stocking at the store.

 

If you want to do a bit of reading, use the SEARCH tool at the top and do a search for P0303 - a fair number of people have had the same issue. Unfortunately it often is traced back to the valves which is diagnosed via the compression test others have referred to.

If that is the case, its time for removing the head and either rebuilding it, or acquiring one pre-rebuilt.

Anyone? Has anyone here described the actual problem with the head/valves?

 

Well GM had TSB's out for loose/improperly installed valve guides, then there was the TSB on excessive valve stem carbon buildup causing stuck/burned valves.

But the preponderance of Cylinder #3 being the "bad guy" in most cases has had me wondering for a long time if there is/was a basic design deficiency in the head design of the Ecotec engines.

My best guess is that there may be a coolant flow issue causing a "hot spot" on that particular cylinder, because not all P0303 misfires don't readily slot neatly into the "loose valve guide/burned valve due to carbon buildup" categories.

And of course you have the coil pack failures, and bum injectors to keep in mind during diagnostics.