Correction, charge air temperature dependent
High intake air temperature gives a negative compensation, which means the ignition timing is displaced to a more retarded value.
Scheme 776
The "catalytic converter heating" function is activated during certain cold start conditions. This function causes a delay in ignition timing, usually after top dead center together with the AIR function, which injects air into the exhaust ports.
As a result, exhaust gas temperature increases considerably and the catalytic converter is warmed up quickly.
This function is combined with slight opening of the throttle to compensate for the engine's reduced efficiency due to delayed ignition timing as well as to increase idling speed. This increases the air mass flow through the catalytic converters.
Scheme 777
Surges (variations) may occur during acceleration. These are caused by sudden increases in engine torque combined with a certain elasticity in the power train and engine mountings. Through compensation, these vibrations can be reduced or eliminated completely.
The anti-surge function detects variations in engine speed and dampens them by influencing ignition timing, normally to a somewhat more retarded value.