Hello all, new to the forum and blazer community. I picked up this 1998 blazer with 100k on it for what I hope will be still a good deal. I've replaced rotting vacuum lines I've found so far. Will check the actuator tomorrow. But what could be broke if 4lo still works?

 

I had the same problem with my 97'. I found out that actuator (bolted under neath the battery try) had a crack in the bottom and the line from the compression type ball on the top right side of the hood was dry rotted. Also just hit it with PB blaster and pull the cable with pliers a few time. After I replaced all the vacuum lines I still had to spray it and just mess around with it.
Good.

 

If it works in 4Lo (drags/binds up on a turn on dry pavement) then everything you need for 4Hi is working mechanically. When you hit the 4Hi button, do you hear the encoder motor attempting to shift position? Does the button light up or flash?


Inside the TFC are two shift forks, one changes the mode (2 or 4) and the other changes the range (lo or hi). If you get 4Lo then the mode is in 4 and the range is in lo. In 2 wheel the mode is in 2 and the range is in hi. The front axle engages anytime the mode is in 4, so if the wheels are dragging/binding up when in 4Lo and turning, everything is working except the encoder motor is not turning to the 4Hi position. Either not being commanded there by the TFC controller, or the encoder is not showing the correct position to the controller.