Chrysler Repair: Chrysler 300M blown spark plugs & more

Question
Hi Kevin,

I drive an '02 300M (3.5L V6) with just under 150,000 miles on it, bought it used with 46,000 in 2006. I've had some engine troubles recently, (what appears to be) the same problem keeps occurring. I'll try not to be long winded, but we'll see.

I took my car in in 2012 because it sounded like one of the cylinders lost compression; I could hear the air/fuel rushing out when the piston was firing - it happened while exiting the highway and I could easily hear the first bang. The shop took a look at it and said it one of the spark plugs exploded (there was a  white residue). They had to re tap and install an insert where the spark plug threads in to the cylinder head. The problem seemed to be fixed.

Then in late november 2014, a similar event occurred, only I didn't see any residue. a different cylinder started leaking. I took it to another shop (new city) and they said the same thing, rethreaded an installed a new spark plug.

Now yesterday I had (what appears to be) the same problem on a different cylinder. I dropped it off at a shop this morning and its currently at a shop getting looked at.

Concurrently, since 2010 or 11 I've had a check engine light on. I will intermittently get p0440 or 0441 code, p0306 code, and p0135. I pep boys suggested replaceing the evap canister, but the check engine light remained, and I had another mechanic do leak check with smoke and found a line that was leaking, and replaced it, but none of these fixes made the engine light go away. ( I was surprised no one suggested swapping an o2 sensor, since seems to be related to the 0440/0441). I did the key dance when I dropped the car off, and it told me I had p0440, p0306 as active codes today.

Finally, I noticed about a year or two ago one of my friends said the engine was idling really rough, I didn't notice/thought it was normal. It doesn't seem to be too bad on the highway. In neutral the idle is a little smoother, but it doesn't always hold a steady engine speed, and can fluctuate from 400 to 1200 RPM.

All this to say there is something going on. Are the check engine light and the blown spark plugs are related, and how do I actually fix the problem? Also, is it common on these engines to have spark plugs blowing up? I'd love to hear your input, even if its that its time to get a new car.

Thanks in advance,

Ryan

Answer
Hi Ryan,
The 0306 says you have a miss on cylinder no. 6, and if that is the latest cylinder to have a problem with the spark plug that would explain the code.
I have not heard of a problem such as you describe with the spark plug hole threads. It suggests to me that a previous owner either did or had a mechanic abuse the threads on several of the cylinders and it may continue to be a problem on more of the cylinders.
The 0440 and 0441 are about there being no recapture of evaporated fuel which can be due to leaks or failed parts of that system.
It does suggest that you may just be in for more problems due to the cylinder heads/spark plug thread history. I can't predict the future with regard to those. A more detailed inspection of the evap system will probably reveal the cause.
Roland