Distributor Advance Unit: Testing and Inspection

Vacuum Advance Test:

Inspection of the vacuum unit can be done with a hand operated vacuum pump, tachometer, and a timing light.

1. Connect timing light and tachometer. Disconnect the vacuum hose connected to the unit and connect a vacuum pump.

2. Connect the timing light to #1 spark plug wire and start the engine.

3. With the engine at idle, apply vacuum and measure the amount of ignition timing advance.

Malfunction Indicators:

Excessive Advance: Weak Vacuum Controller Spring.
Sudden Advance Rise: Broken Spring.
Insufficient Advance: Impaired Movement of Stator Base.
No Advance: Broken Diaphragm.


Refer to COMPONENT REPLACEMENT AND REPAIR PROCEDURES for further information.