Ignition Timing: Notes

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.