Last winter, my 4WD was intermittent. I would change the switch inside the cab to 4WD and sometimes it would engage, other times it would not. I have read on here that sometimes the vacuum pump goes bad and will cause the defrost to run when the heat is turned on, etc. None of this ever happened. I have traced the lines and can't seem to find any vacuum leaks either. My question is, could this be caused by the solenoid that accutates the vacuum pump? Maybe it is bad and telling the vacuum pump not to engage? Is there any way to check voltage on the pump or solenoid to get an answer as to which one is bad?


So I went out tonight and started messing with it some more. I uncoupled a few fittings and now have created myself the A/C defrost switching problem!

Help me out with how this works. Directly behind the battery there is a box (maybe 10" x 6" x 8"). On the left side of this box (looking from the front of the truck) there are two hoses connected. What is this box? The front one has a tee coming off of it the back one does not. The tee connects to a hose that runs down (i'm assuming to the hub???) and the other end connects to a small contraption mounted to the fender. What is this contraption? I want to make sure I know what these parts are from here on out.

I uncoupled the hose coming off of the tee. I heard a hissing sound (this was when the truck was not running). I turned the truck on to check if this hose was pulling any type of vacuum and it did not seem to be. Next I uncoulped the other hose coming off of the box (the one toward the cab) about 1 foot from the box. Again, a hissing sound, it did not seem to be pulling a vacuum. I hooked them both up, took the truck for a drive and noticed when I would put it in 4 wheel or take it out, my vents would change.

What have I done now????

 

Broke it!!

Time to order up the service manual!

jammer

 

X2. Also, I have had issues in the past with ESOF having a delay in engaging and I have found that changing the transfer case fluid works wonders.

 

I am just confused as to why, after taking two connections apart and then re-installing them, I developed a leak somewhere. How can I test that my vacuum pump is working properly and where is it located?

 

Hardened/cracked lines. It might have been sealed originally, but now that it's been removed, a crack may have resulted. You could go to a hardware store and buy some new line and start replacing it. That's what I did on my 2000, seemed to be the cheapest/ less involved route. It worked for a while and then something else gave. I ended up giving up on chasing the leak and going "old school", capped off the lines and manually locking the hubs...