Gradually my engine has developed bad enough misfire, HPTuners shows that most of misfires are in cylinders 2 and 7. I've changed plugs recently to TR-55s. It misfires on WOT mainly, in all revs. I've tried adding fuel to 12:1 from 13.2:1 - no change...
What can it be? Bad plugs again? I was running very rich for some time, could the plugs die from that?

 

Why did you change to TR6s? What do plug 2 & 7 look like? What gap? What mods?

 

Was going to run NOS. Sorry about confusion, turned out I've put TR-55's there in autumn... Actually I took #2 and 7 out today and put old AC Delcos with sharp ends like a needle. Now 3 other cylinders show misfire, with #2 and 7 being below average
The car jerks quite badly, especially with more than 15% throttle on low revs. If I do WOT, it shakes pretty violently, like 3-4 cylinders don't work... I tried to change AFR in quite a large range, it only has minimal effect (with A BIT better doing at 12:1).
So I'm kinda confused now...
Mods - 383ci, low-comp, mild cam, headers, Patriot heads...
I don't know what gap was there, don't they come with some standart gap?

 

Any ideas? Should I think about testing my coils somehow? Or maybe try smaller gaps?

 

Looks like gap on these TR-55's was 0.055.
I've looked under the hood in the dark, there was no arching... Car drives a bit better than yesterday, but now humidity is about 85%, and yesterday, after 2 days of raining, it was 95+%.
Any ideas??
Here is couple of pictures of one of the plugs:

 

I would start with a new set of tr55s gapped at .060. Trying to trouble shoot misfires with questionable plugs will be an exercise in frustration.

 

You're probably right... Although I wouldn't call them questionable with only 2-3K miles on them...

 

Problem solved I've changed another 3 plugs (which had most misfire count), and it went like it should no misfires or anything than I put back 2 NGKs with factory gap (.055), and everything was still fine
I think I just had crack in 1 or 2 plugs
I'm glad ignition is fine if it works with TR55's with .055 gap
Hopefully friday we'll see how it works with turbo

 

yep, they were cracked.

I went through the same nightmare for a week.

You couldnt tell they were cracked, even feeling them. I went through wires, coils, injectors, and plugs...

The porcelain didnt move until I removed it from the socket...doh'

 

I hope if your plannin on spraying you tighten the gap and go to a colder plug.

Glad you found the problem.

 

Yes, will put TR6 if I can find them, or close gap to some .045 if I'll have to stick with TR55's