First snowfall of the season, tried the 4x4 & it wouldn't go in, the shifter was moving properly but the dash light was not coming on & no 4x4.
It eventually did go in after spinning quite a bit, however after switching out & back in it was the same issue.
I'm not sure what's going on, I don't entirely understand how the 99+ system works... I'm disapointed it doesn't work the same as my old 95.
I did swap the drive flanges out with Trackick manual locks as an attempt to save fuel.  Was this a bad idea?

Dave

Check your air line to the front diff at the front cross member were rubber meets steel tubing.

I didn't realize there was an air system, I will have to chect it out tomorrow - thanks.

turn your jeep of put the 4x4 on and turn the key to make electric contact dont start the jeep just put the electricity on you will supose to hear a mini compressor in the front bumper on the side of the passager if it start but only run for 10sec and shut of you have a leak if your not hearing the compressor at all maybe the pump is not good and need to be replace bu these thing are expensive they are like 600$ new but i got one from a mecanic shop for 80 and it work great make sure your connection dont have rust in it .

The pump may be repairable - fairly common problems are loose wires (there is a little circuit board inside) and rust on the dump valve - I have a pictorial teardown in another forum if you want to go that route.