Electronic Spark Advance

In the ESA system, the ECM is programmed for the best ignition timing under every engine condition. Receiving signals which indicates the engine condition from the sensors, e.g. engine revolutions, manifold vacuum, coolant temperature, etc., it selects the most suitable ignition timing from its memory. The ECM controls a driver, (a switch inside the ECM), to ground the coil's primary circuit. Since the coil's primary circuit is grounded, there is no longer any voltage in that circuit, thus high voltage is induced in the secondary windings of the coil. Voltage is then generated at the spark plugs. Thus ignition timing is controlled to yield the best engine performance.