Ignition System: Description and Operation

PURPOSE
The Programmed Ignition (PGM-IG) System used on this engine is designed to control ignition timing to maintain optimum performance and economy in all driving conditions.

OPERATION
A high voltage pulse created in the ignition coil flows through the coil wire to the distributor. The distributor and its rotor will lead the voltage pulse (through rotary motion) to the correct spark plug wire. Through this wire the pulse is led to the spark plug, where it must jump a gap to reach engine ground. When the voltage pulse jumps the gap to ground, it creates a spark (ignition spark) strong enough to ignite the air/fuel mixture in the combustion chamber.
The PGM-IG ECM processes input signals from the TDC/CKP/CYP sensor, Throttle Position (TP) Sensor, Engine Coolant Temperature (ECT) Sensor and Manifold Absolute Pressure (MAP) sensor to determine the correct ignition timing for any given driving condition.The PGM-IG ECM sends voltage pulses to the Ignition Control Module (ICM) unit to trigger the ignition spark.

The Ignition System has two major functions:

Control At Start
Ignition timing is fixed at 7° BTDC for cranking. The cranking is detected by the TDC sensor and starter signal.

Ignition Timing Control
The PGM-IG ECM has, stored within it, complicated "ignition maps" to determine the correct ignition timing depending on engine speed and intake manifold vacuum pressure. Engine speed and vacuum pressure are calculated from the various input devices.
This system, not dependent on a governor or vacuum diaphragm, is capable of setting the timing with more accuracy than a conventional system with governors or diaphragms.