Yeaaa so got a misfire on cyl 4 and decided to pull all the plugs. Boots and plugged lined up from 1-4 in photo. These plugs are only 3 years old BTW. Not sure how screwed I am lol. Cyl 4 boot reaks of gas, none of the others do.

 

Why does the far right plug look like double the size on the threaded portion. I'm assuming it has been blown and heli-coiled ?

 

That plug is a lot bigger! How did that happen? Maybe the owner does'nt know? I noticed the other plugs are rusty. May not be good quality. Get new NGK. The fat one you will have to bring to auto parts store and find a match. The standard coil may not like your improvised plug. You may need a new coil too. Clay

 

Alright so it seems the 4th cyl was helicoiled, but whoever did it didn't use any loctite. Helicoil thread is stuck to cyl 4 spark plug. Cyl 4 spark plug rethreaded hole looks clean.though an none of the threading was damaged. Coil pack for #4 is deff shot. Borescoped cyl 4.

 

Helicoil might not be grounding properly giving the mis-fires and/or the coil wasn't giving very good contact on the plug for the Misfires. Might be a combination of both. Good luck with fix.

I am assuming that loctite wasn't used because it might block the coil from grounding to the head.

 

I've never heard of a helicoil having a ground problem. Instructions usually say to use red locktite on the bore thread side so it's fastened to the head. Not the plug, if you red loctite the plug you'l have to heat the area with a torch to remove it from the helicoil. May be beyond a shade tree mechanics capability. Interesting idea though, is grounding a helicoil a problem?