can't figure out whats wrong

[ford5.0]

hey whats up guy's i have been coming to your site since i got my explorer5.0 to soak up some knowlege but know i have a problem i don't have all that long with my explorer but i purchased it used with 120k miles on it. it runs great but the problem i am having is that the person who traded the truck in put a flow master exaust cat back and a k&n intake (i think its home made) i don't know what else he did to it but since ive own'd it this is the third time that it has fould out my cylinder #3 spark plug when i pull it out the electrode end of the plug is crusty black like build up on it when it happens the check engine lights comes on and when i have it check'd they all ways tell me that its a cylindr #8 missfire but i i check it nothing is wrong with #8 but if i check #3 sure as hell its the same thing if any body could help a newbe i would greatly thank you

 

[snoborder42]

If its always the same cylinder that is getting fouled up and its black, I suspect a slight oil leak somewhere and it is getting into that cylinder.

 

[schmidlkofer]

maybe piston rings or something?

 

[BrooklynBay]

Welcome to this forum! I suspect that it might be a bad coil in the coil pack. That cylinder is not firing properly, and as a result the plug is getting fouled up.

 

[aldive]

Have you checked/replaced the plug wire in question?

 

[410Fortune]

so the computer says misfire #8 but your #3 plug is bad?

I would check my firing order and coil pack wiring first, the explorer has a different wiring pattern then the older Mustangs