Ignition Timing: Description and Operation

IGNITION TIMING AND KNOCK CONTROL
Ignition timing determines the exact point in the four-stroke cycle that the spark plug fires to ignite the air/fuel mixture. In general, the best ignition timing point is one that produces the most complete and most powerful combustion, and the greatest downward push on the piston.
As engine rpm increases, there is less time for each step of the four-stroke cycle. The mixture must be ignited earlier so it has enough time to burn completely. Ignition timing must advance as rpm increases.
If the timing is too far advanced, the spark will ignite the mixture too early. It will burn too fast and too hot, and may cause detonation-violent explosive burning instead of controlled, power-producing combustion. Detonation, commonly called knock or ping, can also cause serious engine darnage.
As load increases, as more power is demanded from the engine, the throttle is farther open and a more dense air/fuel mixture fills the cylinders. Combustion creates more power and more heat, increasing the risk of detonation. Ignition timing must be retarded to compensate for increased load
If ignition timing is retarded too far, the spark will ignite the mixture too late. The piston is moving away and increasing cylinder volume. Power is lost because the burning air/fuel mixture is less dense. Poor combustion also results in much higher levels of harmful exhaust emissions.

Motronic Ignition Timing
The CIS-E Motronic system controls ignition timing according to a complex series of values programmed into the control unit. From a basic setting, the Motronic system adjusts ignition timing electronically to compensate for different operating conditions.