Hi, all. It seams there is a leak on my vacuum pump. If I shut off the engine, the fuel shut off valve lever will go down, the engine will shut off. Then if I look at the lever, it will come back slowly like in 20 seconds.
I tested the shut off valve, and it is good, no air will get in after fully compressed. So then I blowed air in to line that goes to the engine key/vacuum pump, and I can hear air leaking on the vacuum pump.
(Do you know if the start engine key, is supposed to "block air" when on the off position?).
Is this means the vacuum pump is bad?. Will a little leak have some issues like on the brakes, or air conditioning valves, etc?.
Please let me know, Thanks.

Turning the key to off connects the actuator to the brake booster supply line. That's how vacuum, speaking of it as a commodity, gets to the actuator. Turning the key to glow cuts off the vacuum supply and vents the actuator line. IIRC there's a check valve or two between the key switch and the pump. By blowing you move air in the direction not gated by the check valve so that's not conclusive. Seems like you can apply your MityVac to the same line and it should hold, but you might have to draw a vacuum on that gallon chamber of a brake booster for a meaningful test.

Sixto
83 300SD