I am having troubles with my 87 YJ engaging 4WD.
At first it wouldn't do it at all. After a few tests I found that one of the vacuum nipples had rotted away from the front axle shift motor.
So I bought a new one from my friendly Jeep dealer. $280.50 (beyond ouch, for a thing that's little more than an EGR valve)
I installed it. Nothing happened. Still no 4WD. But the 4WD lamp would now light. It would not go out though until I disconnected one of the vacuum lines.
Now the strange part. I disconnected the green line that supplies vacuum in 2WD but not 4WD and plugged it. It plugs into the front face of the shift motor (not the top two nipples). Now almost everything works well. In and out of 4WD drive on the fly. This tells me the shift motor is mechanically okay, it moves the axle collar.
The 4WD light still stays on once in 4WD until I disconnect one of the shift motor lines though.
What do I have wrong?
Also...
Looking at it from under the hood, there is a blue line that comes from the rear and terminates in what looks like an inline check valve. Is it supposed to go somewhere?
Does anybody have/know-of a schematic for the vacuum line routing?
Thanks, Charlie