I have a 1980 240D with a vacuum system that operates the door locks and the engine shutoff. The manual says that the vacuum reservoir tank is sufficient to actuate the door locks ten times without runnung the engine. At sea level to 2500 ft elevation I get about 4-5 actuations. At 6500 ft elevation I can stop the engine but get 0-1 door lock actuation. The system will hold a vacuum overnite.
My suspicion is that my vacuum pump is not generating its design vacuum. In other words it is getting tired.
Does anyone have any other ideas or how I might check if the pump is working OK?