cylinder misfire

[plainsranger]

Hey all,

frequent reader before i registered, but first time poster. Have 4.0 OHV and it has any annoying misfire in the number 4 cylinder. Pulled the code (P0304)
to figure out misfire condition. What i would like to know is truck had the same problem back in July of this year, pulled the plug on #4 and all the porcelain on the bottom of plug was gone. Only thing there was the electrode. Now I am assuming the same thing has happened, (I know, I probably shouldn't assume), what would cause this? Would this be something with the piston or just crappy motorcraft plugs. FYI, truck only has 59000 on clock and when problem was diagnosed back in july, i changed all 6 plugs so all are brand new with less than 3000 miles on them.

 

[97ranger4x4]

well motorcraft plugs are what you want to stick with. They are OEM and I would stick with them.

When you replaced them last, did you check the gap? I think on my 4.0 its from .52-.56

As for what could be causing the misfire other than a inproperly gapped plug. I am not sure and hopefully someone else will chime in.

 

[MAKG]

Detonation can break the porcelain. As can dropping the plug on installation.

 

[plainsranger]

just to let you know, took ranger to ford dealer today and found out through them doing a pressure test on the cylinder that the head is more than likely cracked on that side. When pressure was applied to cylinder, bubbles came back thru the radiator when #4 was at the detonation stage (when both valves were closed), so guess i get to spend 2 G's and get it fixed. Anyway just wanted to let you know and to say thanks for the replies to my question.