Help! My 2001 F-150 Supercrew w/ Triton 5.4 (106,000 M) has developed its third misfire since I bought it new 4 years ago. Since the first was a warranty job (under 30K miles) and the second cleaned my clock (and wallet) at 98K miles, I want to learn what is happening in this techno-motor. At Ford repair rates I will go broke trying to keep this otherwise really cool truck on the road.

My OBDII tool told me I had a P0306 (Misfire in Cylinder 6) which I attempted to correct by replacing the #6 COP assembly (the plugs were all replaced at 100K by the dealer (ouch!) I erased all codes after the repair. Engine ran super smooth for one day! While towing my closed lawn mower trailer the next day, the mis returned, the MIL started flashing (the service engine soon light) and I could feel a slight stumble at speed and at idle lift-off. This miss was not as pronounced as the first, but still noticeable. Also, under load I could hear a ping in the engine similar to the old poor gas-engine knock of yesteryear. Got home, put my tool back on and this time I have the P0300 Random Cylinder Misfire and the P0306 Misfire in Cylinder 6! I really cannot afford the dealer at the moment, and was wondering if any others had any comments or suggestions on this problem.

Thanks for your help!

 

Hi and welcome to the forum

Seeing that the plugs are almost new you were probably fairly safe to assume that the problem was the COP. Since the new COP didn't fix it though you may have a bad spark plug, possibly caused by the COP. A new spark plug is quite cheap so that's where I would start. You could swap the plug and COP with ones from a different cylinder and see if the code follows them.
Ever run any injector cleaner through it?

 

Thanks for the reply, Racerguy! Since low-bucks is what I need right now, I thought I would try the plug next - as you suggested. Never as had the injector system cleaned unless this is a part of the standard Ford service visit. Those I have done. I will try your suggestion (replace the plug and move the COP. BTW - I replaced the Motorcraft COP with a Sorenson unit from my local Advanced Auto Parts Store. I am just not up for another $130.00 Motorcraft COP unit. I checked my service records and this COP has been replaced before (at the 100K service visit.) Any reason why this position would be so troublesome?

Thanks for the feedback, and for the great forum!

 

Number 6 doesn't seem to usually be a problem but the other day when i replaced the plugs on a truck like yours the #6 hole had a bunch of water and rust in it. Maybe the way the engine comaprtment is there is water getting in there easily from road splash?
I don't have any experience with COPs othe than Motorcraft. I work at a dealer so that's what we use.

 

Mine's in the shop right now getting (1) new COP, PCM reflash, and the throttle body/egr/upper intake cleaned, front and rear diff and t-case fluid changed, and coolant change/flush.

66k miles on it. Took it in for a misfire and while it was there they recommended the diff and t-case fluid change, since it's never been done.