Ignition Timing: Description and Operation

Ignition Timing

The ECM calculates ignition timing using inputs from the following sensors:
^ CKP sensor.
^ MAF sensor.
^ Knock sensors.
^ TP sensor (idle only).
^ ECT sensor.

At start up and idle the ECM sets ignition timing by referencing the ECT and CKP sensors. Up to 2003 Model Year, Multiple Spark Discharge (MSD) is used at idle speed to improve refinement and reduce emissions. MSD was discontinued at 2003 Model Year with the introduction of different ignition coils.

Once above idle the ignition timing is controlled according to maps stored in the ECM memory and modified according to additional sensor inputs and any adaptive value stored in memory. The maps keep the ignition timing within a narrow band that gives an acceptable compromise between power output and emission control. The ignition timing advance and retard is controlled by the ECM in order to avoid combustion knock.