I'm getting misfires on cylinders 1, 2, and 4 pretty regularly and I'm trying to diagnose what's going on. The car seems to run smoothly during normal driving, but WOT will cause misfires, some smoke, and backfires.

I initially thought it was my Denso 5353 spark plugs (I wanted a colder plug because of Accessport tune). I took them out last night to check for fouling, but they seem to be fine. I'm attaching some pics of the spark plug from the #1 cyl for more opinions.

Other than the spark plugs, I noticed that cyl 3 never misfires. Last year I had a coil pack fail and I'm pretty sure it was #3. So that leads to my next question: do coil packs need to be replaced as a group? Is it possible I have 1 new coil pack and 3 weak/old coil packs that aren't performing under full load?

Let me know what you guys think.

 

Yes, that is possible, but probably not the case. Swap 3 for another, and then see if the misfires still are on the same cylinder.

Multiple misfires have lots of causes. A bad batch of fuel is high on the list.

 

That's a good idea. I'm going to try this next.

Bad gas is out of the picture, I've been to multiple different stations over multiple months and the issue persists.

 

Carbon build up on intake valves?

 

I second the carbon buildup. When was the last cleaning? Could also be the HPFP.

 

Walnut shell blasted less than 3 months ago. Anyone know if coil packs degrade towards the end of their lives? I'm at 95k and I don't think they've ever been replaced other than the failed one I replaced.

 

Yes they can, especially if moisture has got in. Pull them out and have a look at them. You can sometimes see a lot of rust around the base of the metal, or cracking in the sleeve. If you notice a big difference between the 3 older ones and the newer one then that is a sign they are getting old

 

+1 on the rust and the moisture on the coil . I have seen them pulled out and rust and cracked.

The MCS coil have that metal sleeve, the Cooper ( NON S ) dont. But still get crack or ground out on the insert tube on the head. Look for arching marks also.

http://www.ecstuning.com/Search/SiteSearch/12137575010/