Bosch Vacuum Pump Restriction Test Diagram

Vacuum tester connected between the fuel transfer pump inletside and the primary filter/fuel-water separator 1. fuel filter housing; 2, transfer pump; 3, tester

This test allows the mechanic/technician to determine if there is a high restriction to fuel flow to the suction side of the fuel transfer pump. If there is, the injection pump will not receive enough fuel. This will be accompanied
by lack of power as well as possible rough idling and stalling. Either a vacuum gauge or a mercury manometer can be use to check the restriction to fuel flow. However if a mercury manometer is teed in to the fuel system in place of the special gauge make sure that you hold or mount the manometer higher than the engine. Failure to do this can result in diesel fuel running back in to the manometer when the engine is stop. A low reading is what we are looking here , since this indicates that the fuel lines and connections are offering a minimum restriction to flow at the suction side of the fuel transfer pump.

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