Ignition Management Components Descriptions

Ignition coils up to 99MY
The electronic ignition system uses four double ended coils. The ignition coils are mounted on a bracket fitted to the rear of the engine. The circuit to each coil is completed by switching within the ECM, allowing each coil to charge. When the ECM determines the correct ignition point, it switches off current supply to the coil which in turn causes the magnetic field around the coil's primary winding to collapse, inducing ht voltage in the secondary winding and in the iron core of the coil. High tension voltage, of different polarities, is produced at either end of the coil's core and is transmitted to two cylinders simultaneously, one on compression stroke, the other on exhaust stroke. This is called the wasted spark principle.

Note that coil 1 feeds cylinders 1 and 6, coil 2 feeds cylinders 5 and 8, coil 3 feeds cylinders 4 and 7, and coil 4 feeds cylinders 2 and 3. The resistance of the spark plug in the compression cylinder is higher than that in the exhaust cylinder and hence more spark energy is dissipated in the compression cylinder. Coil failure will result in a lack of ignition, resulting in a misfire in the related cylinders. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.

Ignition Relay:
The ignition relay supplies the power teed to the coils (6.5 amps), purge valve (1 amp, non-continuous) and heating elements of the HO2S sensors (8 amps, non-continuous). The relay is ignition key controlled, when the key is turned off, supply to the coils is immediately cut. Failure of this relay will result in no ignition.

Ignition switch sense:
This is used to initiate the power up and power down routines within GEMS. The input is supplied from the ignition relay. When the ignition is turned on, the ignition relay is enerigised and the GEMS ECM starts its power up routines and turns on the ECM main relay, the main power to GEMS and its associated system components. When the ignition is turned off, GEMS will usually maintain its powered up state for several seconds (up to 20 minutes in extreme cases when cooling fans are required) while it initiates its power down routine. On completion of the power down routine, the ECM main relay is turned off.