I drive a 1998 f150 with 4.6L, recently i got code p0303, misfire in cylider 3. i changed the plugs but didnt put any grease in the plug boots because i still am going to change the wires right away... still get a random misfire, mostly going up hills, but i have come to notice that since i quit using my AC for a few days... the light has gone off and have not had a misfire at all. it still doesn't idle perfectly though. when i changed the plugs, all four of the plugs on the side of the motor by the AC were quite wet, not gas or oil. is it possible that when my AC is on it is leaking into the plug holes somehow... i can't see it happening when it is parked idling though.

 

Take the coil that feeds #3 plug to the parts store and have it checked. Don't think the condensation from the A/C is the problem.

 

i figured it was due to the AC because it only happens when i am or have been running the AC...

my truck has coil packs, do i remove the whole thing then??

also when i removed the plugs the #3 plug i could see on the porcelin or whatever(the white part) that the spark had been arcing up it... and all 4 of the plugs on that side were wet.

 

It sounds like the A/C is the problem. I beleive there is a TSB out for it. Need to put some foam insulation on the pipe. A/C condensation drips down on 3&4 plugs causing misfire.

 

There is a TSB about antifreeze from the hose going to the heater core that crosses over the #4 plug. Haven't seen one about the condesation, but I will look.

 

Roarman, If you have that much water in all four [like you said in your original post]and you can see marks on the plugs I would wrap the hose like lastorms said. As far as testing the coil pack, just remove the bolts holding it down and disconnect the wire harness. Don't know if you have a AutoZone in your area, but they check them for free.