Need help with my 4 wheel drive on my '93 GMC Jimmy with 153,0000 miles. It has the 4.3 motor.
Problem is that it won't engage into 4 wheel HI, It will engage in 4 wheel LO though. Where should I start to diagnos this problem. Nothing happens when I hit the switch on the dash. (4HI only). Please send help. Thanks.

 

I'm no expert by any means, but if it goes into 4lo, then all of the solenoids are probaly working and I would start by checking the 4hi button itself.

 

Check the vacuum actuator... I think it's under the battery, but might be in a different place on the 1st gen... Check a Haynes or Chiltons manual... Should be able to help locate it for ya.

 

Since I have 4LO working, wouldn't that mean the vacuem actuator is still good? Or do they work differently for each position?

 

I think that might depend on if your front wheels actually work or not...

I can't remember if the first gens had the option for the Auto function of the 4x4...