Intermittent misfire resolved

[Stew]

For a month or two I've been able to feel an intermittent and random misfire under high boost conditions. Back before I tuned my car I increased the plug gap to 0.030 and I suspected that the demands of the tune and a few tens of thousands of miles later the gap had increased enough to be causing this. I was wrong.

I had to replace the coil pack. The spring in the cylinder number 4 position had corroded badly.

Here is the bad spring next to a good spring and the issue is obvious:

I'm not sure what caused this, the number 4 spark plug looked fine and very similar to the rest regarding cylinder operation but the outside had some corrosion.

It almost looks like some water had gotten into the plug well on that cylinder, like I had sprayed off the engine at some point and left standing water in there, it definitely wasn't coolant.

 

[ahtoxa]

Good info - thanks for the update. You don't recall ever getting moisture anywhere near there, do you? Any deep puddle dives or anything like that?

 

[Stew]

Good info - thanks for the update. You don't recall ever getting moisture anywhere near there, do you? Any deep puddle dives or anything like that?

Lol, no I don't. I was trying to remember doing that and I may have, but heck half the time I can't remember what I had for breakfast!

Any water had long since evaporated, everything was nice and dry when I replaced it last night but the damage had been done. I also re-gapped my plugs back to the factory 0.025. Ok, I really gapped them to 0.024 but what's 0.001 among friends.

 

[cndctrdj]

ill have to take mine apart again sometime and look

 

[fieldhouse]

I started noticing the engine was idling rough and then got a P0304 check code (misfire, 4th cylinder). I pulled mine apart just now and it looks almost identical. Time to replace.

 

[h2ofreeze]

Same thing here. 123K miles, so not really complaining. Easy to change out.