ok i have a 1995 s10 blazer. i can press the 4hi button and it lights up and i can hear it switch over but still is not in four wheel drive. so i can under there and tried to spin the front drive shaft for the four wheel drive and it does not spin. but it still in two high and it does the same thing for 4lo any one have any idea what this could be?

 

does the 4HI light blink? or go solid, if it stays blinking, its not engaged. and you have to be in nuetral for 4LO to engage.

 

I just had the same thing on my 200 blazer it was a bad vacum hose from transfer case to a module under the battery that locks in the front axle

 

ya it goes soliod.. and ok i will check that vacum hose..

 

This will help with the vacuum lines.
https://blazerforum.com/m_52228/tm.htm