Check engine code P0304

[Gary Mick]

Check engine light lit the other day. OBDII reader said P0304 (intermitant misfire of #4 sparkplug). Vehicle has 46k miles so I bought some NAPA premium sparkplug wires and a new set of plugs (NGK Iridium) and installed. Light has come on again, twice. Any suggestions on what to check next? Thx

[bobs turbo pt]

welcome to the board gary!! maybe a sensor ?? just a thought [:I]

[Hooligan]

Did you use dialectric grease on the plugs before you put the boots on?? That may have something to do with it.[:I]

I changed my plugs & wires with 500 miles on it because I could feel a vibration while idling. I used Champion 7440 gapped at .040 and performance wires from my dealer. I have had NO problems since.

[quicksilverdon]

Welcome, Gary.
First thing to check- that boots are fully seated - push hard 'till you feel/hear a click - they're tough. A little dielectric grease inside the boot helps.
Next I suggest you pull wire off # 4 (both ends) and swap with # 3 to see if it's wire or plug ( if you still get 304, it's plug, if it becomes 303, it's wire). It happened to me (only with plug 2) - after I swapped, light went away! I suspect I may not have had wire seated at one end or the other...