Re: Dying 05 Expedition
x3 on Vac leak.
The TCCM (transfer case control module) might also be to blame here for the 4wd system. It's vac controlled but if the circuit inside gets wet or even moist for a prolonged period of time it can cause issues such as not being able to get it out of 4wd and may not be directly connected to low vac pressure.
Also, check/replace the PCV valve, it's about $6 and takes a few minutes to change out. There's no easy way to find a vac leak, and just hope that it's not leaking behind the dash....
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 75,000m
'06 Pontiac G6 GT 3.5L 220hp; 83,000m
'17 Fusion SE 2.5L 16,000m
Amsoil in all vehicles!