Hi everybody. I hope some of you have some input on this strange miss-firing. I have a 99' with a 4.2L V6 with just over 40,000 miles. It started missing a couple of weeks ago while I was towing some jet skis in Laughlin, NV, in 115 degree weather. The problem went away after I parked it for a couple hours and did not have the problem towing the skis back to San Diego, but the CEL was still on. Then a week later it started missing again. I changed the coil pack, plugs (to NGK), and wires (to good, insulated ones). It would still miss after the truck drove around for about 15 minutes. The code read P0306, miss-fire on cylinder 6 (back, driver side). I haven't a clue what is going on with this truck. A mechanic friend of mine said it could be 1 of 3 things: bad compression on cylinder 6, bad fuel injector, or leak along the intake runner. My brother is mailing me his pressure guage to check #1 and I can use carb cleaner fluid for #3, but I don't know how to check for #2. He also said that if these don't fix the problem, go back to the plugs and wires, etc. There are a couple other things I should mention that might give some insight. When I changed the plugs, they were all clean, even #6 (just that normal light coat of carbon). Also, 4 of the 6 plugs broke as they came out. The electrode just popped out from the middle of the plug, appearing as if the metal electrode had corroded inside the plug. And lastly, when the engine misses while I'm out, the engine feels more unbalanced as I limp home. The unbalance is minor at first, but can get wicked after a little while.

So does anybody have any idea what on earth is going on with my truck? Should I change the injector, etc? Thank you.

 

I have an 01 F150 (4.2L V6) with 138,000 miles. Same problem, except mine has been doing it for quite some time now. I have also changed the plugs, wires, fuel cap, PCV valve, and, just last week, the coil pack (based upon a recommendation from the local Ford service department). Sometimes, the light will go out anywhere from 1 day to 1 month. I have made sure the computer was reset each time and it still pops back up with P0306. I have not done a compression check yet, so it will be interesting to see how your test comes out.