2008 F150 Lariat 5.4 3v Flex stalls and chugs when AC is engaged
 

I have no idea what is going on. I have replaced the FRPS (twice), FPDM (twice), cleaned the throttle body, replaced fuel filter, cleaned the MAF sensor (twice), reset the PCM and performed Drive Cycle numerous times. The same thing keeps occurring. I crank the truck and idle, all good. Turn on the AC and it will run for a few seconds and then either stall or chug like a diesel (black smoke included). At speed everything runs great if I wait until cruising before turning AC on. If i am at idle or in the process of stopping with AC on the darn thing starts stalling and chugging. Sometimes it catches itself and does not stall and sometimes it doesn't. The only codes that pop up are P1000 (due to PCM reset) and codes rendered by the stall/chugging event. If I leave the AC off and run through the drive cycle, no codes appear at all. I am left with dropping the tank and replacing the fuel pump as I am not confident the pump is delivering adequate supply/pressure 156k miles. Anyone have any ideas?

Soooo sounds like your AC compressor is shot, then. Clearly it doesn't want to spin. Doesn't sound like an engine issue at all.

I was thinking that but immediately after the PCM reset the truck will run great and the AC works great (idling or at speed). Not only that but it doesn't rattle or make any noises that would lead me to believe the compressor is bad enough to stall the engine. Not to mention the gas exchange looks excellent on guages and will freeze you out in the 100+ degree heat in N. Texas.

The PCM reset could've worked out because it hadn't re-learned what to do with fuel yet and was over-compensating. Are you having any difficulty when you hit the gas going up a hill?

Not a bit. The truck runs down the road like a champ. Just hauled a 450 4 wheeler in the bed and a 650 Can-Am on a 10' trailer to AR last weekend. AC cranked on tilt. Only stalls when stopping. My FRP stays around 36-39 psi then dips to 0 when chugging initiates and then spikes to over 70 psi when it does recover. Then it settles back to +/- 39 psi.

Try another PCM reset. See if you can duplicate it a few more times.

The graph for the FRP looks like it is spiking continuously during normal operation.

I have a new fuel pump coming this afternoon and will change tonight. I will have to reset the PCM at that time and should have a better grasp on what it isn't.

BTW...I appreciate the feedback as this is not like anything I have seen before.

I REALLY don't think it's the fuel pump... but hey, new fuel pump, I guess... reselling point later