2001 p0304

Got the P0304 code when it was raining out this morning (dropped the daughter off at college in Madison so I really had no choice but to drive the van back to Minneapolis). Check engine light was flashing a few times, severe bucking/chugging, felt like it was going to stall, etc. After about an hour on the highway it finally smoothed out (rain went away too) and the check engine light went off after about 4 start cycles. I replaced the plugs at 129,800 miles (first time at 52K), did the isolator bolts and EGR cleaning at 72K (EGR ports were actually pretty clean so I don't think that's the problem).

At this point I'm thinking it's the coil and/or plug wires, which are original. Van gets regular oil changes and trans fluid changes. Thoughts?

Code P0304 is clyinder #4 (bank closest to radiator) first clyinder. I would take a water bottle and squirt the spark plug wire when it is dark out to see if the wire is bad first, if wire is bad you will see it arking in the dark from the mist of water. I am think9ing wires.

I replaced the coil and plug wires. The biggest problem I had was finding parts that fit. I usually go to CarQuest (I get a fleet discount) and I went through 2 coils and 3 sets of wires to find a combination that properly fit. The caps that fit on the coil towers on 2 different sets did not set snugly- rotating the wire caps caused them to lift up, and didn't quite snap in firmly. I ended up getting an OEM Motorcraft wire set. The guys at CarQuest called a few different shops and it seems this is a common problem with the wires. One tech stated that the replacement wire sets had caps that were just a touch too small in diameter which caused them to ride up on the coil towers. Anyways I got everything bolted back and van runs great. It idles just a bit smoother too. The real test will come when it rains out and see if it misfires again. The OEM coil was cracking on the bottom, so I'm assuming moisture got inside and mucked things up.