3.3TT Spark plug done for, faulty plug or coil?

[Stanger21]

Hi all

I'd been feeling slight stuttering when holding boost in the last month or so and then last week I got a CEL and code P0304, misfire on cylinder 4. Cleared the code and restarted and although the stuttering was worse under heavy acceleration, there was no CEL and the car drove fine before hitting boost. Bad news was I was on holiday so had to baby the car until I got home. Everything was pointing to a bad plug.

Good news is, in preparation for installing my JB4, I had a brand new set of HKS M45IL plugs sitting at home gapped and ready to install. Installed them today (not too difficult after watching every YouTube video going and buying every size swivel socket I could get my hands on) and all seems back to normal. Bring on the JB4.

Question is what could cause my cylinder 4 plug to get in such a state. The car is bog standard and isn't thrashed, 20k miles on a 2021 surely shouldn't need a plug change yet. Am I best changing the coil? Least it's number 4 so probably only a 5 mins job if I do. Pics of the culprit below...

 

[Ozekia]

That looks like a bad connection from the coil to the plug, also is the ceramic cracked as this will cause the voltage to track through this crack to ground.

 

[Alpinesting]

Coil pack is shit.

 

[Alpinesting]

You may want to inspect all of them. These are a problem and they addressed it if you had a warranty.

They leak voltage and jump causing the plug to fail. Replaced ours and no problem. They went bad at

15k. All the models after 2021 got the better coil packs.