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Normal ignition timing

Normal ignition timing


As soon as idle speed control stops, normal ignition timing is activated. The ignition timing now depends on engine speed and load.

The ignition must be advanced as engine speed increases because the combustion pressure would otherwise act on the pistons too late and hence reduce the efficiency of the engine.

A load increase means that a larger quantity of air is drawn into the cylinder during each induction stroke (mg air/combustion). This gives rise to a higher gas pressure with the result that the speed of combustion increases. For this reason, the ignition must be retarded when the load increases.

The ignition timing for each load and engine speed is written into a matrix in the control module memory. The ignition timing is optimized for the maximum engine torque at any one point, which coincides with the best efficiency and thereby the lowest fuel consumption.

The Compensation section, see , explains why normal ignition timing must sometimes be slightly advanced or retarded, as it can also be affected by other factors besides engine load and rpm.