Shift on the fly 4wd not working...but does shift when stopped

[FordSHO8991]

Hi everyone, on my 96 4.0 I noticed this winter the shift on the fly for 4wd high does not work. It did for the three years I owned it prior to this year. It will shift into 4 high when stopped completely though. I have spent the past hour on here looking for an answer and no such luck. I also recently had the valve covers replaced, as well as the cam position sensor, could there possibly be anything associated with the control trac in that area? Any info is greatly appreciated. At least the 4wd still works!

 

[corkey]

only way any of that would affect the control trac is if they left the vacuum line off for the axle disconnect,, follow the lines from the vacuum globe on the front passenger side back to the intake,, and than from there down to the axle,
it's behind the headlight, in front of where the air cleaner is,,