I noticed that one of my vacuum lines was bad on the driver's side. I've done a lot of reading on the 4WD systems and frankly I'm confused now. My understanding is that when in 2WD the solenoid is open pulling a vacuum on the actuators (IWE) which keeps them disengaged. When you switch to 4WD the shift motor on the transfer case sends power to the front wheels and the solenoid turns off the vacuum which engages the actuators sending power to the wheels. Therefore if there is a vacuum leak the actuators won't disengage properly.
Through my trouble shooting I've determined that I think the solenoid is working properly because I'm getting a vacuum when in 2WD and no vacuum in 4WD. I believe that both actuators are engaged and working properly when in 4WD. However, I must not be getting a vacuum to the driver's side actuator (hub) because the line is totally busted up and can't possibly hold a vacuum. However the passenger side line looks good to me. Does this mean that I've been driving around in "3WD"??? I don't seem to have any problems when in 2WD turning (no tire skip or hop). Can someone help me understand whats going on?
Vacuum to the hubs only occurs when switching INTO 4WD (for a period of 50 seconds or so) and OUTOF 4WD (15 seconds or so).
When switching into 4WD, after 50 seconds of "high vacuum" being applied, the hubs should be engaged. The problem is, there is no way for the system to actually confirm hub engagement. So the 50 seconds of high vacuum ends regardless of whether the hubs are actually engaged. If the hubs (or a single hub) do not engage, then that is usually indicative of a vacuum leak.
When switching from 4WD back to 2WD, after 15 seconds of "low vacuum" being applied, the hubs should be dis-engaged. Again, the problem is, there is no way for the system to actually confirm hub dis-engagement. So the 15 seconds of low vacuum ends regardless of whether the hubs are actually dis-engaged. If the hubs (or a single hub) do not dis-engage, then that too is usually indicative of a vacuum leak.
Hence, it's not all that uncommon for one side to work OK while the other side fails to engage/disengage properly, resulting in 3WD.