Ignition Timing Control System

On 1977 manual transmission equipped models, when 4th gear is engaged or the thermo sensor is closed, manifold vacuum at the ignition timing solenoid valve is blocked and no vacuum retard is available. When 1st, 2nd or 3rd gear is engaged and the thermo sensor is open, the air filter passage of the ignition solenoid valve is blocked and manifold vacuum acts on the distributor vacuum diaphragm to retard ignition timing.

On 1977 automatic transmission equipped models, when manifold vacuum is preset value of vacuum switch "B" or the thermo sensor is closed, manifold vacuum at the ignition timing solenoid valve is blocked and no vacuum retard is available. When manifold vacuum is below preset value of vacuum switch "B" and thermo sensor is open, the air filter passage of the ignition solenoid valve is blocked and manifold vacuum acts on the distributor vacuum diaphragm to retard ignition timing.

On 1978-79 models, when engine is cold, the thermo sensor switch is open and no vacuum flows through ignition solenoid valve to the retard side of distributor diaphragm. During cold cruising, carburetor vacuum is applied on the advance side of distributor diaphragm through the delay valve.

When engine is hot, thermo sensor switch closes, energizing the ignition solenoid valve and allowing manifold vacuum to be applied on the retard side of distributor diaphragm. During hot cruising, the amount of retard is decreased by vacuum being applied on the advance side of distributor diaphragm through the delay valve.