Ignition Timing: Adjustments

The Saturn Electronic Ignition (EI) system provides spark energy for air/fuel combustion in response to timing commands from the Engine Control Module (ECM). System components include two ignition coil modules, spark plugs, and ECM.

The Electronic Ignition (EI) system contains input/output circuits and controls two ignition coil modules that house both the preliminary and secondary ignition coils. The ECM evaluates two signals (one from CKP sensor, and another from CMP sensor) to decide when to energize a specific primary coil by grounding an internal driver. This, in turn, energizes the secondary coil (in ignition coil module) which serves to initiate dielectric breakdown on the particular spark plug.

The ECM controls spark advance by monitoring engine rpm and MAP input. Spark retard can occur on an individual cylinder if the ECM detects knock. A particular cylinder is identified as having knock using inputs from the knock sensors and the CMP sensor. Other secondary contributors to spark advance and retard are also evaluated by the ECM.