Checking for vacuum leaks on my Blazer using a small air pump at 2 psig and a pressure gauge. All hoses, valves, and switches check out good at 2 psig, no leaks. Hooked pump and gauge directly up to rear of manifold where the small hose taps off. Can only build .25 to .5 psig of pressure. I have the air intake blocked off and the exhaust pipe. Why can I only build a small amount of pressure? I used a small amount of soap-water leak checker around the gaskets, EGR, and brake booster line and no leaks. Where should I check next?

Thanks for the help.

 

pcv valve?

 

Its a brand new ACDelco. I unhooked it and plugged the hole, no change

 

BUMP...should the intake manifold be able to hold positive pressure? looks like the valves would have to be all seated or you'd have to be really lucky or something. thanks.

 

Well, apparently it wasn't a problem. hooked everything back up, started her up and she held a solid 19-20 psig of vacuum with a steady needle (whew!). Vacuum problem was the wrongly connected hoses on the transfer case switch the whole time.

THANKS!