RakerBill

I own a 00 Jimmy with the 4.3 and 4X4. I recently had to replace the vacuum motor for the blend door.
Now when I go to use the heat controls, all the air comes out the vents in the dash. I can hear the vacuum motors under the dash working, but every setting I use I still have air coming out the dash vents, at least 50% or better.
I can see the blend door moving, but very little like there is not enough vacuum to run it.
I checked the vacuum at the lines going in the firewall and there is only 14 pounds vacuum there, and there was some oil residue in the ends of them at the T by the master cylinder.
Is that enough vacuum? I want to get a reservoir and bolt to the hood to help boost it. I realize under throttle the vacuum will drop, but even at idle the controls are real slow to react or work at all.
Where can I find a diagram as to which lines go to what under the dash. I want to find the problem before the bad weather sets in.
Any help would be greatly appreciated.

stock s10

14 inches of vacuum isn't normal I've got a vacuum gauge permanently installed on my '96 S-10 with a 4.3 and I run an average of 17 inches of vacuum. If I burp the throttle it'll jump up to 22-25. I think you need to check out the rest of your vacuum lines and look for some possible pin holes or spots worn through.

RakerBill

I'm going to check the timing on it. I have had problems in the past with a ford I own, and the vacuum was down. I found it the timing was retarded, and after I advanced it, it was a lot better.
I am also going to check the lines to see where there might be a leak.
The vacuum was pulled right there by the master cylinder, not directly off of the menifold.

stock s10

That is actually the best spot to do a vacuum check because it's supposed to have the largest volume for the brake booster. As far as the timing goes, on a 2000 it would be computer controlled and there would be no advance or retard that can be changed by a person.