I pulled this plug out of cylinder 6. So the XJ didn't really "eat" it, but there was a chunk missing. I don't know how bad this could really be. If it was a faulty plug, or something else happened.

 

What was the gap at before you put it in and what is the gap at now?

 

is the engine mkaing any kind of ticking noise??? running rough??? if not i wouldnt worry about the little piece of ceramic that is missing. that piston may have a little scarring but more than likely not. how old is that plug??? may of just been a bad plug. ive seen a few do that.

 

And when was the last time you checked/changed the plugs? It never fails to amaze me when some folks drive the **** out of their XJs, change the plugs once every decade and then are surprised when they see something like this...

 

I would be worried about that missing chunk getting lodged in a valve seat.

Start the engine up (for a second) with that plug removed and see if it blows that chunk out.

 

"or something else happened"

Detonation

 

X all^.. You sure that's the correct plug? The porcilyn seems longer than I remember.... or not, just a thought.

 

The gap is at .035. It's the same size as when installed.

 

The engine has always had a slight tick, or tapping. Is quiets when accelerating. Doesn't go away when it's hot though either. It's not loud. The plug has about 3k on it I don't drive the **** out of it. Short trips to work, the occasional drive into the city. It has been running rough, but I've been contemplating a faulty o2 sensor, that I'm having trouble removing. The upstream seized in the socket. The idle seems better now, but take into consideration, I just changed the plugs.

 

That's an odd plug...porcelain shouldn't be that far off from the threads. Secondly that's detonation as someone said (using mobile app else id out your name in) and possibly also overheating. Are all your plugs that style? They really don't seem right

 

They are all that style, Champion model RC12LYC. Have it right in my hand.

 

Just read up on this. If this is the case, how do I stop it?

 

Put NGKs in it.

 

Pretty sure 97+ is supposed to run RC12ECC...

+1 cruiser's recommendation for NGKs. ZFR5N is as cheap as the Champions

 

NGK performance plug made in Japan.

Bunch of others made in china by Wunhung Lo and his buddies.. Crappola. Bosch sucks.