P303/P304 Codes

[capwater]

Every 3 months or so I get these codes being thrown (1997 Explorer V6 100k miles). Misfire cyl 3 and 4. Runs fine, full power no hesitation. Easy/cheap fix thus far is replace the two plugs and I'm good to go. This is a spare/kid's car so it doesn't see many highway miles. I seemed to get more time between plug changes when I was driving it to work (35miles highway roundtrip daily). Since they are on opposite heads I would likely rule out some type of head issue. Plugs look good when I pull them, no fouling or oil. Wires are maybe 30k old so I wouldn't think that, though I may swap them around as a test. Bad coil maybe frying the plugs? Any thoughts? Thanks!

 

[DirtyDog]

I would say either bad wires or a bad coil pack.

 

[CAHUNTERMAN]

Are you loosing any coolant? I have the exact same issue in my 99 4.0 OHV but I'm loosing coolant into the cylinders which I suspect is destroying the plugs. Since mine is also cylinders 3 and 4 I'm guessing the intake manifold gasket is leaking coolant into the cylinders or I have two bad heads or head gaskets which like you said, seems unlikely.

 

[capwater]

Yes, coolant is leaking! Cyl3 is driver side back and cycl4 is passenger side front, diagonally aligned. Looks like I'll take a look at the intake manifold gasket. Thanks for the info.