I have a 2005 F150 with 5.4 and have been having increasing random misfires. This is MUCH more pronounced when the engine is warm, and I can certainly count on it to happen when under load, either accelerating or whatever. If I am forced to remain stopped for any extended period of time, such as waiting in line at a drive through, then start to drive again, the problem seems to increase exponentially, and is most pronounced in the 1300 - 1900 RPM range. If I take the overdrive off in order to put the rev's above 2000, it eases the problem, but does not eliminate it. The issue is much LESS pronounced when first starting driving, it seems to be most prominent only after it warms up.
So far, the only codes I have ever seen is random misfires, and only once has the code gone solid in the ECM. Usually, if I back off load for a minute, it clears up on it's own and the flashing code light clears .... If I attempt to accelerate hard, even when cold, the misfires get really bad and I can always expect a hard code soon afterwards ...... needless to say, I have no real power at any time, and my fuel efficiency is beyond bad (best I can get is about 11 mpg) ....
HELP !

 

Some of the fellows should be along shortly with some pointed questioning.
Do you still have Torque on your tablet?
Might help to have the specific pcode handy.

 

Oh and Fellas...
The op is my Dad, so ya'll treat em right eh?

Welcome back to the forum Dad!

 

Yes, I do still have Torque and a couple of others on my tablet, and phone - however, so far I have only seen it actually set a readable code once - but I have not really tried to watch it while driving ........
I really think whatever it might be may be something that is heat sensitive, or even something that "accumulates" when I am sitting with the engine idling - it ALWAYS gets MUCH worse right afterwards ....... SOMETIMES, it eases up a little after a few driven miles, but sometimes it does not.

 

Most of the mis fire issues I have seen with these trucks have been due to the spark plugs. How many miles do your plugs have on them? Are they motorcraft plugs?