I have 2008 F250 Crewcab XLT 6.8L it has an intermittent misfire, and when it is misfiring the A/C compressor kicks out blower blows but no cold air and you can hear the compressor cycle. just as soon ad the miss goes away the compressor cycles and BOOM cold air. My Geneysis scan tool is at OTC getting repaired so all I have is a pocket quickie code reader, P0356 is my code. also has a p04446 evap code it has had for months. I am looking for pointers to even begin looking. I am going to swap coils, but if I understand the code correctly, it is a control circuit issue. possibly a ground side switch from the ECM.

 

I swapped coils and cleared codes p0446 is still present drove with no issues, I will have to go for a longer drive, the retainer clip on the #6 cop is broken and there was little resistance to pulling it off, if the connection was bad it could look like an open in the ground signal, I am still baffled about the A/C. I had an 04 Lincoln LS V8 that would shut the air down when a cop was causing an bad miss, but I work on a fleet of 20 plus superdutys and have never had the complaint with a misfire. And the drivers would never fail to complain about an A/C issue!

 

Did you add an extra 4 in the code? P0446 is for Evaporative Emission system vent control circuit. It means there is an issue with the gas tank vent. The most common cause is missing gas cap or bad O-ring on gas cap. But it could also be an issue with the vent plumbing at the tank or the circuitry that controls the gas tank vent valve.

 

the p0446 really does not concern me it is an evap code does not affect drivability. the miss was my biggest concern, I still do not understand the A/c cutting out but the plug on the cop harness must have been loose and the cause, I drove it all day today with no issues.

 

Ya when your pcm detects a misfire the computer shuts down all non essential accessories. It will also flash the engine light to let you know to shut it down so you don't damage your cats

 

That is correct. The AC is "non-essential".

That depends on the severity of the misfire. It only flashes the MIL if the rate of misfire exceeds a calibrated limit for a Type A misfire.