Electronic Spark Control (ESA)

Electronic Spark Advance (ESA) Circuit:

PURPOSE
This system controls electronically the time of electric current flow to ignition primary coil as well as ignition timing.

OPERATION
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.

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

CONTROL
Control of this system includes three 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 turns ON), ESA system sets the ignition timing to the initial ignition timing (5C BTDC).



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.

Ignition Timing = Initial Timing + Basic Ignition Advance + Various Compensating Advance.


When the idle switch is ON, the ignition timing is determined by adding basic ignition advance, 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 fuel injection time and coolant temperature compensating advance to the initial ignition timing.

Coolant Temperature Compensating Advance - This compensation is added according to the signal from the coolant temperature sensor which detects the engine coolant temperature. The amount of compensation is larger when the engine coolant temperature is lower and smaller when higher.

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, ESA system controls the time of primary current flow to the ignition coil.