I just bought my very first F-150 2 days ago - 2003 F-150 Lariat V8 5.4L 125.000 miles, had it checked at the mechanic before signing the paperwork, everything was fine. Yesterday afternoon the CEL came on, took it to AutoZone and it came up with code P0306 for a misfire on cylinder #6. They told me some Sea Foam might help, but unfortunately that was not the answer. It still studders and rumbles while driving. Any Ideas?

 

Have you tried anything other than snakeoil, seafoam. Probably gonna need to change the plugs, use motorcraft only and torque to 28 ft lb . New boots on you coils. If you still have a #6 misfire swap #6 and #5 coil to see if it moves to #5. If it does replace coil. If not swap injectors on same cylinders. Trying to narrow it down to a certain part. Good luck

 

Thank you so much for the input! ... I took it to a mechanic who loves F-150s and it looks like somebody dumped it in the mud ... had all spark plugs and boots replaced ... #06 also needed a new coil ... runs like a baby again and I am a happy woman! Hopefully in the future and starting with small easy stuff I will be able to take care of some issues myself ...