Thats fantastic, thanks for all the help guys. I will check it out tonight!

 

Ok, so I went out last night and looked and didn't see anything really loose under the hood. If it wasn't in the teens and snowing last night I would have gotten under the Blazer and looked at some more stuff.

How much on the vehicles are controlled by vacuum? It's starting to bring back memories of my old 83 RX-7 that was a vacuum nightmare.

 

near as I can tell its just the front axle lockup, HVAC controls, and the usual brake booster.
on the 2nd gens fuel pressure is too but the regulator actually sits inside the upper intake plenum in the middle of the 'vacuum' in there so there's no hoses to crack or rip.

as part of my troubleshooting I looped the hose for the vac reservoir onto the stem for the t-case (the one i've got disconnected right now) so that all that was actually connected was the small black hose headed into the cab - vents all worked again like that. Then I found the reservoir, hooked it up proper and plugged the line to the t-case - everything still worked. Then I hooked back in the line to the t-case and everything stopped working - poked around under till I found the leak and soon that'll be fixed too...

 

I found the problem and got it all fixed. I kinda feel dumb for not being able to find the problem right away, but I've never really worked on theses Blazers before. lol


After looking at all the pics that have been posted and researching it more here on the forum I discovered this.



The whole hose was gone and I never noticed it when we did the motor swap. The hose goes from the check valve to the top of the manifold.



After I put a new hose on, the air will now switch between the defrost and the vents, and the 4x4 works. Who woulda thought huh.lol Now I am wondering how much the missing vacuum hose affected the performance and MPGs. We have been getting horrible mileage and I am not sure if this had anything to do with it.

Thank y'all for posting all the info and sharing pics!!

 

I've been getting horrible mileage too - hoping to see that improve up to terrible again for awhile.

Note on the OP about the starting issue: Still got the problem and I'm pretty sure it'll turn out to be the infamous poppet valve/injector failure - for now letting it sit at 'ON' for a few seconds before twisting it to 'START' is keeping me going.

if the poppets are bad once i get those fixed hopefully i can get to 'poor' from 'terrible' for MPG.....

 

OK - ISSUES CONFIRMED.

as i suspected-vaccum lines. I went in and replaced 3 or 4 cracked, open, and collepsed lines. Suddenly, everything works again no issues. Magic, it took ten minutes and did it in my work cloths (dress shirt/pants). Thanks for all the help guys. I appreciate it.
MORAL OF THE STORY! ALWAYS START BY CHECKING THE OBVIOUS...