how do i test a vacuum pump and vacuum booster? i have hooked up a vacuum gauge to the the line coming from the pump @ the distribution manifold and with the engine running i have 26.5 inches of vacuum. when i turn the engine off ,i lose all vacuum in about 45 seconds. is this normal? should the vacuum hold for a extended period of time? any info is appreciated. thanks mark p.s. i have an e 350 van ,1985,with a 6.9 diesel.

 

There should be a check valve at the brake booster inlet.
Otherwise vacuum should 'disappear' with the engine off.
(at least this is true with gas engines, but there is nothing driving the pump with a diesel either)

 

sounds normal to me. You should be able to pull the check valve out of the booster and tell if its been holding vacuum. It should hold for days, if not you could have a leaky booster or check valve.