Sonded like a knock while driving, stopped at a mechanic and he felt a coil on plug, making the most noise, front passenger cylinder, No 4? After I removed the coil I found it damaged, the plug was loose,when I went to loosen the plug it was loose, and it was missing the electrode completely. I had a Ford 5.4 Triton engine that blew out plugs 3 times, it's such a common problem you can buy a repair kit that taps a new sleeve and plug in the cylinder, I wonder if one of them would work on the Jag? Or what is the best way to fix it?

 

Bugga,

We use Helicoils if you can at teh hole, and a 3ltr would be testy at best.

A "nut sert" is another option.

That Ford fix sounds OK also.

Most spark plugs are the same thread, 14mm from memory.

For the electrode to be mashed, it must have hit the piston, so maybe the wrong plug from the go get.

 

A new problem for an S-Type I think. Been here 7 (*) years and still something unexpected pops up.

Not an OE plug I'd say!

edit: (*) I meant nearly 9

 

When my Ford spit out a plug it took the coil on plug with it, the Jag didn't so it wasn't as noticeable, I haven't figured out why the electrode was missing though.

 

Someone put in the wrong kind?

 

Are the threads in the head stripped?

 

Typical of like generation Ford engines, since there are only 2-3 threads to hold that plug in. Usually the root cause is use of "hotter" plugs, which expand the threads in the head, eventually leading to a spark plug projectile.

On the Ford F-150 forum, the recommended fix is the "sert" job per Grant's post, and OEM plug only (aftermarket, platinum ones are usually the culprit).