Chevrolet Repair: Where to check vacuum, air fuel mixture, manifold vacuum

Question
Hello. I have a 95 K1500 ext. cab, 305 TBI, 5 spd. man. trans., 247K miles.  I'd like to check the vacuum level and would like to know where the best place is to connect the gauge. Also, I've been told there is ported and manifold vacuum. Could you tell me what the difference is between the two? Thanks.


Answer
Hi Craig,
Manifold vacuum is the vacuum in the intake manifold, that sucks the air fuel mixture into the cylinders. That is what you want to check, and the line that goes to the brake booster, or the hose that goes to the vacuum reservoir is where you need to check it.

Ported vacuum is usually in a fitting tapped into the throat of the carb, or throttle body, and is above, or right at the closed edge of the throttle plate. It measure different than manifold vacuum, and acts differently, and is used to operate things like vacuum advance, egr valve, etc.

Van