This probably won't help but it's worth a try just to eliminate one more possibility. Pull that vacuum hose that goes into the hole in the drivers side fender out of the fender, plug the loose end of the hose with something, now see if the 4 wheel system works. If by some miracle it does work, you have a leak in that vacuum ball inside the fender. Worth a try I guess.

 

I just fixed a friends that would pull the actuator but not quite enough to lock the diff , it was the vacuum line disconnected at the vacuum ball in the fender....reconnect and all's good.

 

To test the actuator push it in by hand and put your thumb over the end of the nipple. It should hold vacuum and stay compressed for a while. If it doesn't it's bad. If it is staying in do the same test on the end of the hose with 4hi selected and idling. You should feel the vacuum. If you have a gauge you should have around 15 in. If no vacuum follow the line back to the Transfer case switch, It is above the encoder motor. Those have been known to go bad and either stick in 4wd or not work at all. Be sure your new one is the improved model with the blue stripe. Dorman ones tend to leak around the hoses. Delco is better. Look over all the lines to be sure they are tight and not cracked.

 

So now my truck is stuck in 4hi
i removed the old encoder, manually turned it to 4hi and put a new encoder motor. Put everything back together. Now it’s stuck in 4hi

Anyone know how I can test all vacuums? I don’t know how to test for vacuum issues.

Thanks.

 

I took it to a mechanic. Faulty 4x4 switch

 

Thanks for the info , I didn't see the last post or you could of been checking all the vacuum stuff last weekend , lol ...maybe a good thing.

 

how to check the switch!

 

Yeah I learned a big lesson: test first don’t guess.

The Haynes manual hardly helped. I guess an official GM repair guide would have saved me several dollars

On the bright side it now shifts so much faster into 4x4. This technology must have been cutting edge during the 90s and yet it still impresses today.

 

Mechanic said that was the first problem in the circuit. Probably an electronic diagram would help diagnose. Cleaning any contacts might also help.

 

thank you I will try that first!