I'm currently dealing with the same problem with my 05 f150.. After 45-50 it chugs down real bad.. Its been getting worse, I have to drive without o/d.. The dam thing has no power band, only between 2 and 3 rpms, over or under is all sputters..

has new

Plugs
injectors
fuel filter
vct things


no catalytic converters

leaning toward camshaft phasers.. thinking one or both banks are stuck, either timing advanced or retarded??

last thing that comes to mind is, the ford tech I talked with said my oil pressure was dropping at random intervals and there is a nasty ticking from the timing region.. It started as the that faint vct cicking and has gotten way worst

 

maybe a bad coil plug,my truck would stumble at 45 mph and it was a coil plug that only missed under load.Also did you use motorcraft plugs,you should also clean the maf sensor(with maf sensor cleaner)and clean the throttle body aswell...goodluck

 

i had one dead cyl 5 before in mine 4.6 07 turns out the coil shorted out and took the computer with it, it killed the pcm coil driver for the cyl only rest of the computer was fine.

if this is your case, it doesnt matter how many time you switch the coils, the code will always stay on those cyl(s) cause the computer is never sending the signal to return it so there for it thinks its a misfire, if you switch coils, the code will still stay there. i do agree with using motorcraft plugs, and i have been hearing good things on the i believe denso irduim i know i spelled that wrong.

maybe this might help a little, however mine said exctaly which coil was bad. that to lean code is usally caused by a vac leak, but then again it usally effects both sides (banks) of the motor. only other thing would be a o2 sensor, but they rarely if ever go out. i know there supposed to be "checked" like every 100k i believe. whats making this odd to firgure out is only one side of the motor is doing it.

 

If you have a misfire it's either a coil pack or plug. Most times in the cases I've seen if its a bad miss then it's a cop. If its a miss that happenns while in overdrive under a load it's more than likely a plug.

 

I have a 2005 F 150 with a 5.4 3 valve engine I have cured the random misfire problem I put in a brand new set of Accel super coils and new spark plugs in the problem went away completely you can buy these on Amazon for $209

 

Good luck with the Accel coils, they don't last.