Last year I did a 3.4 swap on my 1991 pickup. Last week when I was at Les Schwab getting my tires rotated and balanced, the mechanic pointed out that my front differential was locked and shouldn't be. Turns out that the for last 10,000 miles I have been driving around with it locked up. After some brief investigating, I have determined that the problem is with the function of the VSV's. I have been able to get the diff. in and out of four wheel drive but only by switching the vaccum lines around.
The way I found this out was because the Red VSV is getting a constant vaccum no matter what I do, and the blue never creates a vaccum. I really would rather not put in manual hubs. What I need to know is, Since Offroad Solutions is now out of buisness, is this an wiring problem with their harness? Or is this prablem being created elsewhere?

 

You could try switching the wires. If that doesn't make a difference then the vsv itself is bad. If it does something, then it's an electrical issue telling the vsv to activate.

 

Sounds like the VSV may be leaking possibly?

 

Yeah it could be a bad VSV. I had my check valve fail and it wouldn't engage. I was manually switching the vacuum hoses too. The ADD system is pretty simple actually. The vacuum line goes into a booster container above the front passenger wheel then back to the VSV distribution area. You might be able to swap the hoses that go to the differential. Then check to see if the VSV's activate when you put the truck in 4wd. The red one is for 2wd and the blue one is for 4wd. If you have a multimeter, test the pink/green wire when you are in 4wd and see if it sends a voltage. If not you might have a back ADD Relay. For now you should be able to either switch the hoses or wires and get it to stay in 2wd. Then you have to find the problem and see if you can fix it so it'll go into 4wd. Good luck!

 

I can get it into 4wd and out by switching the tubes, I am just wondering why the RED VSV is constantly getting a vaccum, and the blue never does? No matter what I do it still vaccumes. What tells the relay to accuate the VSVs anyhow?

 

The ADD relay is controlled by a switch in the transfer case, when 4wd is engaged the switch closes and the relay switches power from the 2wd vsv to the 4wd vsv. The 2wd vsv should have constant vacuum until you put it into 4wd.

http://www.off-road.com/trucks4x4/ar....jsp?id=399612

 

Exactly. If you put it in 4wd and the blue vsv doesn't engage then there is either a problem with the relay, the wiring harness, or the transfer switch.

 

I dont think it is the Transfer switch because the dash inticator lights up when I engage the 4wd vsv. Relay?

 

Finally Figured it out. For some reason the relay was not getting the signal to close the relay switch circuit. The wiring harness that ORS made me must not have been made correctly. There is a dark green wire that goes to the ADD relay that is supposed to close the circut (to engage the 4wd VSV) when the transfer switch is engaged. The wire was aparrently not connected after the swap. I solved the problem by splicing a wire into the green wire and running it to the ADD wires of the ORS harness. This completed the circuit and the 4wd is now working great. Thnx Guys!!