Ignition System: Description and Operation

Ignition Timing Control:
The programmed ignition (PGM-IG) used in this engine provides optimum control of ignition timing. A microcomputer determines the timing in response to engine speed and manifold vacuum. The input signals are transmitted by the TDC/CKP sensor, CYP sensor, throttle position (TP) sensor, engine coolant temperature (ECT) sensor, and MAP sensor. This system, which is not dependent on a governor or vacuum diaphragm, is capable of setting lead angles with complicated characteristics which cannot be provided by conventional governors or diaphragms.

Basic Control:
The control unit has stored within it the optimum basic ignition timing for operating conditions based upon engine speed and intake manifold pressure. With compensating signals from sensors, the system determines optimum ignition timing and duration for ambient conditions and sends voltage pulses to the ICM.




Compensation of ignition timing

Control at Start:
Ignition timing is fixed at 8° BTDC for cranking. The cranking is detected by the TDC sensor (cranking rpm) and starter signal.