Bare with me through my long story, trying to get it all right the first go around. I have a 2006 Ford F150, king ranch, 4x4, super crew 135k miles. I bought the truck and shortly after noticed the miss under a load at 40-60 mph while in OD, or at higher RPMs at WOT, but never a CEL. Well 3 months went by and I couldn't take it anymore so with lots of research I decided to change the plugs. Ran seafoam through 2 tanks of fuel prior to this job to break up the carbon in hopes of none of the plugs breaking. All 8 plugs came out with no issue and I replaced them with the Motocraft SP 515s (old ones were very nasty and brittle, most likely the original). I put copper anti seize on the end that goes through the channel in the head, however none got on the end near the electrode, and also on the threads. Put it all back together and it had the worse misfire an pretty much not drivable....flashing CEL and codes p0308, p0355, p0356. So I decided to buy 8 new coils as well, got all 8 of them on and now the truck is drivable but the miss is still there (no CEL). Feels like maybe just one cylinder and I believe I got it pin pointed to cylinder 8. I put a vaccumm gauge on it and unplugged the injectors 1 at a time and cylinder 8 is the only one that there is no change while unplugged. So I switched out the coil thinking maybe I got a bad one, still does it. My COP electrical plug has 12v Constant and also confirmed with an led it is getting signal. The injector is ticking or pulsing as i confirmed with a mechanic stethoscope. What am I missing????? Today when I get off I plan pulling the spark plug, checking for carbon tracking, check compression, check actual visual spark, and pull and clean the injector. Any input and advice will be very appreciated.

 

Sounds like you got a bad plug. It happens sometimes. The p0355 and p0356 codes were the coils not being connected all the way. Put a new plug in ASAP the cat converters don't tolerate misfires very long.

 

Also has a new fuel filter, but Yeah I'm not driving it at the moment until I get it running right, I will try that. Thanks for the help.

 

It was that cylinder 8 spark plug. Replaced it with another new one and it runs like a beast let out the zoo now. It's sad you cant even trust brand new parts anymore.

 

sometimes the misfire is the result of a bad or sticky injector, my o6 with 5.4 at 35,000 miles developed an intermittant miss and cel light, changed out the plug and coil on #8 and problem went away for a week, then cel light came back on, ran two cans of seafoam through it and changed gas stations and problem went away. These engines were known to have injector issues on 05 and some 06 model year 5.4 engines, is engine funky to start or does it start normal, hope this helps.

 

I had the same issue,
First sway your injector out, there $25-$40 bucks i had that and a load tick and man did a new injector make a big difference.

 

glad you figured out it was the plug. I was gonna say swap two of em, but good deal!