Ignition System: Description and Operation

PURPOSE/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 Top Dead Center/Crankshaft Position/Cylinder Position (TDC/CKP/CYP) Sensor, Throttle Position (TP) Sensor, Engine Coolant Temperature (ECT) Sensor, and Manifold Absolute Pressure (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 Ignition Control Module (ICM).

Control at Start:
Ignition Timing is fixed at 7° BTDC for cranking. The cranking is detected by the TDC Sensor (cranking rpm) and Starter signal.