My 2000 F150 5.4L threw a code the other day. Upon having it scanned, it was for a cylinder 1 misfire. I was driving down the highway and the AC started blowing warm air, the engine still ran normal, and the check engine light began flashing. I slowed down to about 55, the light flashed for 30-45 seconds, then the AC started blowing cold again and the light stopped flashing. Happened again yesterday, driving around 50mph and the AC starts blowing warm, CEL flashing for 30-45 seconds, truck still runs normal and accelerates, then the AC starts blowing cold again, light stops flashing. Code is still for a cylinder 1 misfire.

I figured if it was misfiring, it would be like other vehicles Ive been in and would hesitate, shake, etc. The only things that seems to be happening is the AC starts blowing warm, then returns to normal. I did notice a very small amount of coolant on top of the engine, appears it could be coming from either the crossover tube or from the hose going into the cross over tube on the passenger side.

So, from the above, what are your thoughts?

 

Fix the misfire and you'll fix both problems. The PCM is intentionally disabling the A/C during the misfire event.

Misfires are most commonly caused by spark plugs and the COP failing.

 

Going to try and knock it out this weekend, at least its cylinder 1. Just found it odd that during the misfire the truck still ran and accelerated normally. Thanks for the info about the pcm disabling the AC, that answers that question.

 

Yeah, I'd suspect there to be substantial performance degradation during a class A misfire (flashes MIL).