Ford Vacuum System Troubleshooting Steps & Tests - Supply, Leak, Component (EVTM)

This page is a service procedure covering troubleshooting of an automotive vacuum system, likely from a Ford EVTM (Electrical & Vacuum Troubleshooting Manual). It outlines six orderly troubleshooting steps: verify the problem, narrow the problem (using the EVTM), test the cause, verify the cause, make the repair, and verify the repair. It notes that vacuum system problems fall into three groups: leaks in hoses/connectors/motor diaphragms, pinched lines or clogged valves, and faulty mechanical operation of vacuum-motor-driven parts. Three tests are detailed. The Vacuum Supply Test (Figure 1) connects a vacuum tester to the system side of the check valve; with the engine running the gage should show approximately 15 inches of vacuum, and if vacuum fails after shutoff the check valve or tank should be replaced. The Leak Test (Figure 3) uses a vacuum gage and pump in place of the tank, clamping supply hoses one at a time with needle-nose pliers until vacuum stops dropping, then tracing the circuit. The Component Test (Figure 2) uses a hand vacuum tester to verify each component holds vacuum and operates correctly. Diagrams identify the check valve, vacuum tank, distribution block, servo, vacuum motor, vacuum pump, and vacuum gage, with hose colors blue and black shown in Figure 1.