I have an 04 FX4 with 5.4. It recently started running really rough during high acceleration. Usually have to really get on it. The CEL starts flashing and then turns off after about a minute of normal driving. The engine runs perfectly smooth during normal cruising. Its just during acceleration and then it quickly goes back to normal. Has anyone had this problem?? The only code it shows is P0306 (cylinder 6 miss fire). Could this just be a bad coil pack for #6?? Im confused as to why it drives and runs completely normal until i basically floor it. Any suggestions would be GREATLY appreciated.

 

how many miles are on it? P0306 is a bad plug, Coil (you don't have "pack" you have COP ignition) none functioning injector or little or no compression in that cylinder. If you never done the plugs and it has over 60k start there then get a coil then swap the injector then compression test..

 

pull the cylinder 6 coil and leave it plugged into the harness. Put the tip of a long screwdriver into the spring inside the boot and put metal part of the screwdriver next to something else metal (about 1/8" away). Wear gloves and don't touch any part of the screwdriver that is metal. Have someone crank the truck over for a second or two and look for a spark from the screwdriver to the metal object. If there is no spark withing a few seconds of cranking, the coil is bad, if there is a spark its probably your sparkplug. If you light yourself up you wont die, but you aren't being careful enough...and its a sign the coil is good too lol.

 

Its a relatively new motor with only about 25000 miles. It was replaced a few years back. I guess ill start with the plug. So that can cause a misfire at high acceleration and engine load? Ill also do the coil test. Thanks for the info.

 

also check down in the hole where the spark plug is. I remember on my '97 i was driving and the cel started flashing at me...programmer told me it was cylinder #1 misfire. Pulled over and removed the spark plug wire (because that year had coil packs not COP). Looked down in the hole and there was a ***** leaf or something in there not allowing a good connection from the wire to the plug.........How did it get in there? only God knows but I removed it and POOF, problem solved.

 

Did you put new coils on the new motor? they are made to last 100k+ if your over that they do wear out. Does it have motor craft plugs? if not these engines are picky about plugs most off brands do not last..