Is this a sign of a loose spark plug?

[greasemanicure]

I went through the threads about changing spark plug wires on my 96 4.0L OHV Explorer. I found a number of threads about spark plug types and one showed plugs with a long reach, but only 5 or 6 threads even though it was as long from tip to seal as ones with all threads.

I pulled #3 as the cylinder has been dead. The plug is all carboned up on the unthreaded part and also blackened on the flats and even the ceramic and the connector at the top.

The plug offered typical resistance to remove it. Even so, might this plug have been poorly seated and leaking since the last plug change? If so I need to "thank" the mechanic who last changed plugs.

I say #3 was dead in that my timing light would not trigger when clamped onto the #3 spark plug wire. Changed the wire which was broken in the retainer, but still #3 was dead. Changed the plug and #3 was back in action.

Any thoughts?
Joe

 

[gavin]

I had a spark plug blow out on me once...
the ceramic blew out of the metal.
talk about getting a lot of looks around town with a cylinder blowing out the spark plug hole.


if the plug was good and snug, then no, it wouldn't have been a faulty install. Well, unless the threads were cross-threaded. But it doesn't sound that like was the case if you got a new one in.

 

[greasemanicure]

That must have been quite a show! Lights! Sound! Action!

Looking closer at the plug, it may leak around the ceramic. The blackening near the upper end of the metal part of the plug looks a bit flared as though the leaks were concentrated at maybe three points around the plug. Just for giggles I may clamp an air hose to the business end of the plug and see if it leaks under pressure.

Thanks!
Joe