I have a question that has been bothering me for about a month now. I purchased a 99' blazer in near perfect shape. I am having the same 4wd problems as others on this forum and I think I have it narrowed down. At the top of the engine compartment in attached to the upper part of the firewall, there is an electronic solenoid with two vac lines connected to it. One runs to the engine supply to provide vac and the other, well here's the problem. It is broken off and I can see about a inch of it just hanging there. I have searched and searched and cannot figure out where this runs too. I have purchased one of the haynes books and it's completely useless. I have also tried to figure it out and no luck. When I press 4wd it pulls vac, when I press 4lo it pulls vac, when I press auto it does nothing and no vac while in 2hi. Can someone help me find it's home?

 

This vacuum line goes to the vacuum actuator under the battery tray. Sounds like the solenoid is working perfectly. You will not get front axle engagement when in Auto4wd until the PCM/TCCM sense slip in the drive train.

 

I have lost day light but will search for this in the morning... Thanks for the fast reply and I'm so happy I can post now.. hehehe I have done alot of reading on this web site and have received so much info it's priceless...