i have been trying to fix this ghost of a misfire on cyl 5 for some time now with no luck, i have put all new plugs in it a new coil on 5 (wich is now on 6 to make sure it wasnt a bad coil) and a new injector on 5, the misfire occurs around 3200 rpms and causes the truck to feel like it has no power and shake like a mad mad when it is misfiring. i am stumped please help me fix it, o the truck is a 2006 f150 xlt with the 5.4 and 44000 miles

 

Did you re-check the gap. Had a similar problem when the dealer put all new plugs in my '07 at 1750 RPMS. They pulled all the plugs re-gapped them and voila - problem went away. Just a thought.

 

Another major problem when you have certain misfire issues at certain rpms is EGR leaks or a clogged EGR valve.

At 44,000 miles, it might be a little gunked up depending on how hard your run it.

 

The 5.4 doesn't use an EGR valve. Check all the wires that lead to the coils, pay attention to any spot that could have rubbed through on another engine component, a clip holding it in place, anywhere vibration could have caused a wire to short or ground out.

 

Not intimately familiar with these engines, but do they have a crank trigger or do they get the trigger from the camshaft? Maybe look there. Are you sure it is just one cylinder misfiring at 3200RPM?

 

TRUCK IS FIXED!!!!!!!!!!!! it ended up slowly getting more and more misfires on all cylinders on that bank and i fixed it today with new high flow cats!!!!!!!! man what a head scratcher that one was