I have been working on this problem for a few months now, so here's the back story. I bought the truck over a year ago, it had the slow fill issue and a p0446 evap code. I replaced the evap canister, filter and purge control solenoid. Slow fill problem gone, but the evap code persisted. I checked all the wires, I have 12v at the harness and good continuity across the ground circuit. Next I tested out the FTP sensor, and not 100% sure it was good swapped it out. Still have the code. I have checked all the hoses for restrictions bends holes..etc and nothing. I also tested out the new vent solenoid to be sure it's good and tested the vapor control solenoid under the hood. I'm not sure where to go next. This is a hard code also, clear it and it returns instantly. Anyone with some advise?

Thanks in advance.

 

My advice would be to follow the procedure in the PCED in order to diagnose it..

 

Just got mine fixed.
My problem was a wire that had worn through just enough that when the truck was moving (just driving as usual) it would short out. It was a pain to find the wire.
My rub through wire was under the air filter plastic shroud. On my 99 ford expedition 5.4l.
But yes i understand the frustration. Hoph this helps some on your search for your problem.
Ps it frustrated me for about 2years.