I bought a 99 Expedition this sumer with 50K. Had it looked at by my mechanic before I purchased. He said to replace the fuel filter (which I did) and replace the plugs (which he did). 2 days before we were to head out of town for Thanksgiving my wife reported a loud banging noise and the service engine light came. Pulled the codes and got P0304, #4 cylinder misfire.

Upon changing the plug wires, I discovered the #4 wire chewed up and cracked. Replaced the wires and the Expy ran fine. Added about 3/4 quart of oil too because it was low from the last oil change a week ago. Some of the oil spilled on the engine.

Everything worked well over Thanksgiving (except for getting a flat while 4x4'ing and ruining a rim) until the ride home. The Expy started to buck again and the Service Engine light came on. It seemed like preignition or Deiseling in a cylinder. Limped along through 40 miles of the mountains in West Virginia until I got to an auto parts store. Read the codes again, and still had P0304 misfire. Pulled the plug wire and found oil had seeped in around the plug and plug wire. Cleaned the plug wire, replaced the coil pack in the parking lot (I was getting desperate), and proceeded on. No Service Engine light. Ran well for 2 miles, then bucked once or twice. Still no Service Engine light, so I pressed on. Eventually, the engine cleared itself, and for the second half of the trip the engine ran fine.

I'm going to pull the codes this morning. The big thing is I don't have confidence the problem is really solved. Suggestions?

 

You need to find out where the oil is coming from and make sure that the plug is properly torqued so that it doesn't blow out of the head.

 

The oil source is from when I spilled it.

What is the proper torque for the spark plugs?

The problem is worst on the freeway. I go to accelerate, and the Expy doesn't down shift right away. It's like driving my '95 f-150 with a 5 speed manual, being in 5th gear and trying to accelerate at 40 mph. The engine just doesn't like it.

 

I stopped on the way home today and Expy is showing no codes per Murray's Auto Parts scanner. It is a basic scanner and didn't count the number of misfires.

 

Torque for the plugs are 14 ft/lb
Normally until you've had a significant number of dead misfires, you won't get a code.