4 wheel drive

theres a vacumn accuator under the battery u can get to it by removing rs inner wheel well u need to see if its getting vacumn while in 4x4 if not theres a check valve/w3 ports that goes bad always on your transfer case when you remove valve if the ball is stuck in or trans fluid in it , replace it good luck your problem sounds like a loss of vacumn to the accuator i told you about in the start