Spark plugs
 

https://cimg4.ibsrv.net/gimg/mustang...fe4ab5e0dc.jpg
I]Just changed my plugs I have a 2005 gt all my old ones looked like the on on the right except that one on the left can anyone tell me why only one was this bad?[/I]

Which cylinder did the dirty one come out of? Is there anything unique to that cylinder in terms of pollution controls? What I'm thinking is, I've seen instances where the PCV gasses were recirculated at a point that effected one cylinder more than the others. Just a thought.

Was the engine running Ok in the first place and this plug change was just a routine maintenance thing? No misfires, etc? If so, I'm not sure I'd worry about it. There's almost always one cylinder, assuming you've got more than one, that's a little different from the rest.

Good luck,
Steve R.

yea it ran fine it was just preventive because I didn't know when they were last changed they look like the stock ones by I'm not sure it was out of the top right looking at it from the front of the car I sprayed pb in each one and soaked it for 36 hours before I tried to take them out