Carbureted Engine

Fig. 45 Ignition timing control system.:

Exc. Federal & High Altitude CRX HF

This system, Fig. 45, uses a dual diaphragm distributor, thermovalve and a cold advance solenoid (auto. trans.) to allow additional vacuum advance during cold engine operation. Intake manifold vacuum is applied to diaphragm chamber A at all times, providing vacuum advance for normal operation.
Vacuum is applied to diaphragm chamber B through a thermovalve and, on automatic transmission models, a cold advance solenoid. When coolant temperature is below the thermovalve calibration temperature the valve is closed and vacuum is applied to diaphragm chamber B. When coolant temperature is above the thermovalve calibration point vacuum applied to diaphragm chamber B is vented to atmosphere.
In addition, vacuum applied to diaphragm chamber B on automatic transmission models is controlled by a cold advance solenoid. This solenoid is operated by the emission system electronic control unit to provide closer control of vacuum advance during cold engine operation. Voltage is applied to the solenoid by the ECU. When the circuit is completed, vacuum is transmitted to diaphragm B; when the circuit is open, vacuum signals are blocked.

Fig. 46 Ignition timing control system.:

Federal & High Altitude CRX HF

These models use conventional centrifugal and vacuum advance units, and an electronic ignition timing control unit and the emissions system electronic control unit to control ignition timing, Fig. 46. The emissions control unit monitors engine and vehicle operating conditions through a group of sensors, determines the ideal ignition timing and transmits digital control signals to the ignition timing control unit. The ignition timing control unit converts these digital signals to analog voltage signals. These voltage are transmitted to the igniter unit in order to shift the phase of the primary current in the ignition coil. The phase shift allows ignition timing to be advanced 5° or 10° from the basic mechanical advance setting.