S83p 4wd problem

Hello everyone
I have a 1993 s83p hijet that's been sitting a while. The 4wd function doesn't seem to work.
I know where the vacuum actuators on the transfer case and the front differential are. But I don't have a clue where the 2 VSVs are or what they even look like. If anyone has a picture of location and what they look like that they can post , it would be greatly appreciated

 

I found the VSVs under the driver's seat

 

Jim,
Did you decide if this was your issue? Also, what does VSV stand for?

 

VSV stands for vacuum solenoid valve, and as the name implies it is controlled electronically by the switches and directs engine vacuum to the 4 wheel drive servos. Failures can be electric or vacuum. listen for a clicking sound at the VSV when the switch is turned on/off indicating that the valve is working. Check all hoses for condition and tightness. There is a vacuum accumulator tank that should be checked for damage or leaks. Finally check the little foam filled air filters on the VSV - they could be blocked with dirt / mud etc. Small wasps seem to like to fill these with mud and eggs ???. You can check the operation of your servos by applying vacuum ( sucking ) to the hoses. They should operate freely. The one on the rear of the transfer case may have a frozen linkage. My S83P with high and low range has 3 VSV's, and I had all of the above noted problems, but when sorted it works very well. Good Lusk

 

Thanks for the replies. I still haven't figured the problem out yet. I tested the 4wd switch . It has 12vdc to it and switch works . I don't seem to have any voltage going to the VSVs. I know there's a switch on the transfer case , but haven't looked at it yet. I don't feel like crawling under the truck. I was thinking it might be easier to pull the bed off to check the switch and wiring

 

Do you have the charcoal canister bypassed or unplugged?

Also the light will not come on unless your actuators are seeing vacuum. Post a picture of the vacuum lines near the valve cover/top.

I had this issue where the vacuum and breather lines were swapped. Getting it correct fixed both front and rear awd.

The charcoal canister also cannot be disconnected or awd will not work either.