Ignition System: Description and Operation

Purpose and Operation
The ignition power module (IA) controlled by the PCME supplies the low tension voltage to the ignition coil which generates high tension pulses for the sparking plugs via the distributor ignition (DI). Depending on the engine speed and supply voltage, the dwell-period (dwell angle) is determined and the ignition energy is adapted to that required at any instant in time. The unnecessary consumption of energy in the ignition coil is thus prevented. In addition, a peak coil current cut-off facility prevents current from flowing through the ignition coil below a specific engine speed and, therefore, prevents the battery being discharged and the ignition coil overheating.

Unlike conventional ignition systems the DI has no centrifugal or vacuum advance mechanisms and no LT circuitry. The DI is only required, therefore, to distribute the high energy (HT) pulses to the sparking plugs.

Ignition timing is controlled by the PCME from information supplied by the MAFS and CKPS. This information is used to access a mapped look-up table containing ignition timing angles pertaining to 16 engine loads at 16 different speeds. Ignition timing is modified by air inlet temperature measured by the IATS.