Well, before it was a misfire in cylinder #4...replaced plug, wire, and coil pack which did not solve problem. Took the vehicle to Ford and they advised it was a carbon build up in the cylinder. They cleaned it out and the truck ran great. Now CEL is back on and DTC says misfire in cylinder #3. Rather than take the vehicle back to Ford, anyone know how to clean the carbon out of the cylinder. I'd say compressed air, but want to make sure. Also, can anyone think of why this is occurring besides the carbon build up? BTW, truck has all new plugs. Could this have anything to do with the fuel injectors?

 

I have...
1998 Ford F150 4.6L 4X2

 

My first move would be to replace the plug wire. If the current wire is the original one, it's probably shot.

 

This is a copy of a reply I just made on another thread. You should try doing a search of the forum.

There are about 10 different things that can cause a misfire code. You have started with the obvious, coils and wires. You should start it up at nite and rev it up to check for arcing from the wires. The next thing I would try is cleaning the throttle body. Sometimes the EGR and/or the IAC becomes clogged with carbon. Here's a good link for OBD codes.

http://www.obd-codes.com/trouble_codes/generic/p0300-ra...re-detected.php

A code P0300 may mean that one or more of the following has happened:

* Faulty spark plugs or wires
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector(s)
* Burned exhaust valve
* Faulty catalytic converter(s)
* Stuck/blocked EGR valve / passages
* Faulty camshaft position sensor
* Defective computer