Two years ago I did my 150k mile (and most recent) complete tuneup, and when I went to remove spark plug #5 at that time, it just about wouldn't budge. I don't recall having any such spark plug problems before... but for some reason at 150k miles that #5 was a bear to remove. I did get it out, and to my surprise the threads on the plug looked ok w/ no extra metal or chewed threads. Then when I went to put the new plug in (with anti-seize), it wouldn't finger tighten past about 1 or 2 revolutions. I carefully tightened it the rest of the way with a socket, and it was rough going but I got it tightened and never had anymore problems with it... until now.
Over the past few days I've noticed a definite misfire under acceleration, but it isn't constant... it comes and goes. Well today I pulled a P0305 #5 misfire code. I put new wires on and it made no difference. I inspected inside the distributor cap and everything looks uniform (ie #5 doesn't look any different than the others). So I hesitantly tried to remove plug #5, and just like last time, it's really hard to turn. I backed it out about 1 revolution and then chickened out - it wasn't getting easier, it actually started getting harder to turn.
I am fairly (but cannot be completely) sure that I never cross- threaded it - I always finger tighten the plugs. I'm perplexed because the plug threads looked ok after I fought to get it out last time. I've come up with 4 potential explanations for this new misfire:
1) Some plug holes just become stubborn, and maybe I inadvertantly damaged the plug's insulator while trying to get that new #5 installed last time, and maybe it's now starting to bleed voltage in a short circuit on occasion. This is my best case scenario.2) Maybe the threads did get damaged or crossed despite my finger tightening rule and despite the threads looking ok last time I had the plug out after fighting with it. Rust or crud could have hitched a ride into the threads 2 tuneups ago and welded the plug in place. The idea here is that it's losing compression or something due to screwed up threads. (Can damaged threads do that? Maybe time for a helicoil?)
3) Could be coincedental. Maybe injector #5 is clogged or bad.4) Could be much worse... worn or damaged valve or seat, blown head gasket, cracked head, etc.
So I suppose my question to you all is, does it sound like the "stuck" #5 plug could be related to my new #5 misfire? Which, if any, of my 4 explanations sounds most valid? Any suggestions? I'm scared stiff at the thought of trying to remove that plug right now.
thank you... dakota2112