When I shift into 4hi or auto 4 wheel drive the light will flash but if I let off the throttle sometimes the light will stop flashing then start blinking again under power. I'm suspecting a vacuum issue. I checked the actuator under the battery and the diaphram seems to be working but the light still flashes! Any suggestions appreciated !

 

I agree that it is quite possibly a vacuum problem. When you look at the actuator, the engine is at idle, correct? This would be a reasonably high vacuum scenario. Off idle or part throttle events will cause a considerable drop in vacuum which should be managed by the check valve and vacuum reservoir to allow for the vacuum operated accessories to keep working properly. If there is a large vacuum leak (cracked or disconnected line) or a problem with either the check valve or the vacuum reservoir, it can result in your situation.

Check over all of the vacuum lines. Given that you have the Auto4wd option, you have the NV236 transfer case which does not have a vacuum switch mounted on the transfer case. This is good in that it makes checking the lines that much easier. I created a vacuum schematic that should be in one of the 4wd related Tech Articles that will help you identify the lines and what they should be connected to.

If you run through all of that and still experience this issue, we can move further so please let us know the results of your underhood vacuum line inspection.

 

I can't find your vacuum schematic in the Tech Article section.I'm kind of technologicly challenged so any help would be appreciated LOL Thanks.