Electronic Spark Advance

ESA System Diagram:

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 a signal to the power unit.

The power unit turns ON and OFF the primary current of the ignition coil according to the signal from ECM.

Control of this system includes four different types as follows.

- Ignition timing control at engine start
- Ignition timing control after engine start
- Electric current flow time control

Ignition Timing Control At Engine Start
To obtain better starting performance of the engine at the engine start (when the engine start switch is turned ON or the engine speed is lower than 500 rpm.) ESA system sets the ignition timing to the initial ignition timing (5° BTDC).

Ignition Timing Control After Engine Start
The ignition timing after engine start is determined as follows so that the spark occurs at the most suitable timing for each engine condition.

IGNITION TIMING = INITIAL IGNITION TIMING + BASIC IGNITION ADVANCE + VARIOUS COMPENSATING ADVANCE

When the idle switch is ON, the ignition timing is determined by adding basic timing advance which varies according to engine speed, temperature compensation advance and compensating advance for idle speed stability to the initial timing.

When the idle switch is OFF, the ignition timing is determined by adding basic timing advance which varies according to engine speed, intake manifold pressure (engine load) and engine temperature compensating advance to the initial timing.

Water Temperature Compensating Advance Characteristic:

Engine Temperature Compensating Advance
This compensation is added according to the signal provided from the temperature sensor.

Compensating Advance for Idle Stability
This advance is provided to stabilize engine idle speed.

Electric Current Flow Time Control
To stabilize the secondary voltage generated in the ignition coil to a proper level, ESA 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.