Bought an '11 Vic with the 4.6L back in June and a few months back I tried to change out the plugs. All came out ok except for cyl 4 which only cranked out 1/4 turn. Had a shop take it out and they said they had to redo the threads. I've seen videos where you can remove a stuck plug by drilling into it somehow, but because this was in the 4 position and hard to get to I'm guessing they just power cranked it out. Not sure but I'm guessing those threads are compromised now.


Well, this past weekend that same plug blew out of cyl 4. Inspection reveals a coil and boot jammed up underneath the fuel rail and a plug that I fished out without any turning. When I go to install a new plug it just sits on top of the threads and turns without going in. So I guess what's happened is that the plug rotated most of the way out but when it got to the last couple threads the compression blew it out the rest of the way, and that it's just the top few threads in the hole that are damaged. Inspection of the plug reveals that most of the threads are intact except for the 2-3 that are closest to the element.


So my question is...should I try to fix this myself or just take it to a shop? Some kind of tap tool would probably fix it, but since it's the beginning threads that are boogered it'd probably have to start from the inside of the cylinder. I really don't have a clue as to how to approach this.

You could use a thread chaser and try to clean up the existing threads.
The concern is bits of debris dropping into the cylinder. But generally a few very small aluminum bits arent a huge issue..
Using a chaser with some grease applied in the fluting to capture anything while running the chase, then if need be you can also crank the engine with the ignition disabled to blow anything out prior to startup.. Chasing the threads usually doesn’t create any debris concerns though..