The encoder motor shifts transfer case in and out of 4W
Vacuum is seperate from encoder motor.
In 4W the front drive shaft is engauged.
On yours if it does not shift out of 4W to 2W or show 2W on lights check transfer case and front drive shaft for locking in and out.
http://www.automotiveforums.com/vbul...d.php?t=572914
Check for codes on yours by grounding pin 13 on diagnostic connecter and watching the shift button lights.
Post back codes/button flashes.