cparke

With a vacuum gauge connected to the small vacuum line which is normally connected to the fuel pressure regulator, when starting the engine I observe vacuum slowly increasing to 20 psi as the engine warms up, but as soon as I turn off the engine, a sudden drop to 0 psi.

Should the intake manifold maintain some vacuum pressure with the engine off?

qezel

you're gonna have some valves open.. so the second you turn the engine and it's no longer drawing air.. bye bye vacuum

kenny (dremel)

that's normal.

Kris Hansen

There is a vacuum reservoir, but it's small, and not connected to the FPR line.

cparke

I'm surprised, even with some valves open, that there is a way for air to pass directly from the exhaust into the intake manifold. Could opening the secondary combination valves give me an easier way to block off the exhaust so I can use a hand pump to recreate vacuum in the intake manifold? (yes, I know there is no leak in the vacuum reservoir section, which is held when the engine isn't running by a check valve)

I really would prefer not to have to disconnect every vacuum line and check them individually to confirm no vacuum leaks anywhere in the system.