Ignition Timing

Ignition Timing
The ignition timing is an important part of the ECM adaptive strategy. Ignition is controlled by a direct ignition system using two four-ended coils operating on the wasted spark principle.

When the ECM triggers an ignition coil to spark, current from the coil travels to one spark plug, then jumps the gap at the spark plug electrodes, igniting the mixture in the cylinder in the process. Current continues to travel along the earth path (via the cylinder head) to the spark plug negative electrode at the cylinder that is on the exhaust stroke. The current jumps across the spark plug electrodes and back to the coil completing the circuit. Since it has simultaneously sparked in a cylinder that is on the exhaust stroke, it has not provided an ignition source there and is consequently termed 'wasted'.

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

Function
At engine start up, the ECM sets ignition timing dependent on ECT information and starting rev/min from the CKP. As the running characteristics of the engine change, the ignition timing changes. The ECM compares the CKP signal to stored values in its memory, and if necessary advances or retards the spark via the ignition coils.

Ignition timing is used by the ECM for knock control.