Spark Timing Control (STC) System

Fig. 90 - Thermal Vacuum Valve Specifications:

Fig. 91 - Thermal Vacuum Valve Specifications:

Fig. 92 - Thermal Vacuum Valve Specifications:

1. Check that vacuum hoses are properly connected and distributor vacuum controller is functioning normally.
2. Connect timing light and start engine when it is cold.
3. Check timing while water temperature indicator reads below "C", then run engine until pointer on gauge reaches middle position.
4. Timing should advance as engine warms up. If not, replace thermal vacuum valve.

Thermal Vacuum Valve
1. Drain approximately 1 & 1/8 quarts of coolant from vehicle, then remove thermal vacuum valve.
2. Inhale air from port of spark timing control system and check that thermal vacuum valve opens and closes according to specifications--Figs 90 to 92.

CAUTION: Do not allow water to get inside thermal vacuum valve.

Vacuum Delay Valve
1. Remove vacuum delay valve.
2. Blow air from port on distributor side. Air should flow freely.
3. Blow air from opposite port. Resistance should be greater than in step 2.
4. If condition of valve is questionable, dip port in water and blow air from brown face side. Air bubbles should appear.