Description

Fig. 25 Vacuum controlled spark timing control system. (Typical):

Fig. 26 Electrically controlled spark timing control system. (Typical):

Refer to Figs. 25 and 26 for typical spark timing control systems. Complete system schematics are located in ``Vacuum Hose Routings.''




The spark timing control system is used on California models and is designed to control distributor vacuum advance in order to reduce HC and NOx emissions. A thermal vacuum valve in the system detects coolant temperature and, by means of wax expansion, opens or closes the line from the air cleaner.




Ignition timing is controlled by the central electronic control unit which has been programmed to provide optimum timing under all driving conditions. The control unit used various signals, including coolant temperature, engine RPM and engine load, to determine ignition timing. The signal from the control unit is transmitted to the power transistor of the ignition coil which control the timing.