Plug fouling

[da2962]

After a long trip last October I noticed the engine running a little rough. Took it in to the mechanic and he found one plug (the #5) was fouling. All the other plugs were fine. He replaced the wires as a matter of course, replaced the one plug and it ran fine for a little while, but now back to the same problem. I'm not too handy when it comes to working on the newer engines but am wondering what might be causing this. He mumbled something about a possible valve job, but while he's a nice guy, honest and reliable, he's probably not the greatest mechanic in the world. Any help would be greatly appreciated.

 

[ChasAld]

Had the same problem a few months ago with #4 plug. Turned out to be the coil. Swapped in a used coil from another 4.0L and solved the problem.

Charles

 

[wood1]

There is a fair bit of info on the fact that the 4.0 intake manifold gaskets fail after a while and #5 is the cylinder that tends to show problems...

When I first bought my '93 XLT I was forced to run high test to prevent a bad spark knock and was using a fair bit of oil. I retourqued my intake manifold after reading about this problem and now have no oil use issues (other than the rear main seeping a little) and can run regular grade with no trouble. Make sure you get all the bolts, there are a couple that are hiding...

http://www.explorerforum.com/forums/showthread.php?p=1467822

C.