Ignition Timing: Description and Operation

This system controls electronically the time of electric current flow to ignition primary coil as well as ignition timing. ECM judges the engine condition by using signals from various sensors, selects the most suitable electric current flow time and ignition timing for that engine condition from among those prestored in its memory and sends an ignition signal to the igniter (power unit). Control of this system includes three different types as follows.
a. Ignition timing control at engine start (initial ignition timing)
b. Ignition timing control after engine start
c. Electric current flow time control

Ignition Timing Control at Engine Start (Initial Ignition Timing)
To obtain better starting performance of the engine at the engine start (when the engine speed is lower than 500 r/min.), IC system sets the ignition timing to the initial ignition timing (5° BTDC.) Also, the initial ignition timing (5° BTDC) is restored when all of the following conditions are met.
- Diag. switch terminal not grounded
- Test switch terminal grounded
- Idle switch ON
- Engine speed lower than 2,000 r/min (rpm)





Ignition Timing Control After Engine Start
The ignition timing after the engine start is determined as follows so that the spark occurs at the most suitable timing for each engine condition. When the idle switch is ON, the ignition timing is determined by adding basic ignition advance which varies according to the engine speed, coolant temperature compensating advance and compensating advance for idle speed stability to the initial ignition timing. When the idle switch is OFF, the ignition timing is determined by adding basic ignition advance which varies according to the engine speed and intake manifold pressure and coolant temperature compensating advance to the initial ignition timing.
- Coolant temperature compensating advance: This compensation is added according to the signal from the engine coolant temperature sensor which detects the engine coolant temperature.
- Compensating advance for idle speed stability: This compensation is carried Out to stabilize the engine idle speed.

Electric Current Flow Time Control
To stabilize the secondary voltage generated in the ignition coil to a proper level, ignition control system controls the time of primary current flow to the ignition coil.

NOTE: The ignition timing is controlled by ECM as described above. Therefore, when checking or adjusting the ignition timing, the ignition timing must be fixed to the initial one by grounding the test switch terminal.