"once it hits overdrive at about 45MPH @ 1.2k RPM when i accelerate gradually the truck seems to misfire and has a major vibration/ bucks a bit. when i accelerate more it smooths out."

I had a problem with the exact same symtoms. If I took it out of overdrive, the problem would go away. The problem really showed up under low RPMs and a little bit of lugging.

Took it to the dealer. Took the head mechanic out for a ride and showed him the issue. Immediately he said "misfire". They replaced the plugs and one coil and now it is all fine.

I told the head mechanic that I had the plugs replaced a year ago and much less the 60k milee service interval, and he said "we have found they go quicker, better to replace them more often so their don't get siezed". Well, there ya go.

 

I definately feel your "random misfire" pain @country-dan, - because I have been through exactly the same frustrating issue the above quote describes. What finally FIXED it is so simple - I believe everybody misses the mark on this common problem.


My personal experience (and FIX) is extensively documented in the thread at: https://www.f150online.com/forums/v8...ml#post5159499 with followup reasoning documented at https://www.f150online.com/forums/v8...ml#post5161039


I hope this helps.

 

Thank you for posting this. I had not seen it before. You've got solid shade tree mechanic knowledge, IMHO. This line is kicker: "When I got through, the new spark plugs screwed all the way down to the seat with my fingers just like putting them in a new engine. Then torqued them down appropriately. Upon startup, INSTANTLY - BINGO - perfect startup"

Why would we ever replace a part and NOT have it feel like NEW? Threads don't feel perfect? MAKE THEM feel perfect.

OP, you really should read the thread he linked. My advice was going to be that you should try a few full throttle runs. A couple times getting on the freeway, full throttle up to whatever speed you feel safe at. My truck threw a code after a full throttle run and the code lead me to a bad COP at cylinder 2. After reading F150Torqued's post though, your fix might be following his example.

 

@slo5oh


Thank you for the kind words. I hope relating my experience can help someone. I don't have particularly impressive credentials (truly just a shade tree mechanic), but hyper analytical.


I also could be overly biased. But having FIXED my random misfire problem without doing ANYTHING MORE than cleaning the carbon out of the cylinder head holes and installing new plugs, I am definitely a believer. I did NOTHING ELSE WHAT-SO-EVER during that plug change. Then the subsequent plug change (50,000 mi. later), not a single plug broke. Of course, I cleaned the carbon out of the head again. No misfires at all after that either. To this very day, Mode $06 test with my scan tool (Torque Pro) reports ZERO misfires in the last ten drive cycles.

 

thanks everyone for the insight, its frustrating to go through the expense again once I paid a ton of $$ the 1st time (having a few break). its even harder with my work schedule but luckily i drive a work vehicle so my truck typically i have been putting only 50 miles per week on my truck for the last 6 months or so...

 

my '06 5.4L had a misfire that sounds similar to your.
Changing the plugs fixed it.