I'm having issues with my 4x4 and need some help. The 4x4 light is on even thought I have it on 2H. But when I put it on 4H from 2H the light shuts off, wierd. The 4x4 does not engage when I put in on 4H. I did a vacuum test on both the black and red hose and I find that for the black one it did not hold any vacuum and for the red one it did hold. I performed the test while the truck was on. The truck is a 1997 with the 5.9. Thanks in advance for your help. : )

 

Here is a diagram of the vac lines on the 4WD system. Not sure what line is what but you should have vacuum at least one at a time(2WD or 4WD red/black). Do you have any issues with the hvac doors going to defrost? If so your check valves may be bad and not holding vac to work the hvac/4WD actuator. Also check the metal vac lines that run along the frame to the cad. They can get damaged or rust up inside.

 

One line will supply vacuum to the actuator, while the other will be open to vent. You want vacuum on the INBOARD line in 4x4, and the outboard line in 4x2. Sounds like yours are backwards.

 

Ok, I'll have to look into the check valve and the hvac doors. Thank you for the feedback!

 

It did cross my mind that I might have the vacuum lines mixed up somehow. I'll look into it. Thanks for the feedback!

 

Turns out I had the vacuum lines crossed over which was causing the 4x4 light indicator to stay on while on 2H and turn off while on 4H. I Made to correction and the light indicator went back to normal and the 4x4 engaged. Thank you so much for the help!