Been trying to figure out the 4wd on my 1991 Loyale 4wd with push button on the shifter. Ive found out i have a electrical problem and the vacuum solenoids are not operating properly. But I have switched the vacuum hoses on the solenoids so it should try to engage and the light on the dash comes on but it still acts like it doesn't want to go in. When you first let out of the clutch it makes kind of a grinding noise and is not in 4wd from what i can tell and if you gas it after underway it makes that same grinding noise. Any advise would be great it seems like the pin or whatever engages the 4wd is not being pushed or pulled far enough to engage it properly.

Maybe there is a hole in the vacuum diaphragm. Try actuating the rod itself by hand, to make sure it is moving all the way to make an engagement.

 

This electrical circuit, solenoids, and diaphragm setup are the same for central diff lock units on xt6 and rx, as far as other vehicles to get the same parts from.