Abstract: The invention is concerned with a control system for an air/fuel ratio measurement and adjustment system for an internal combustion engine. In order to limit operation of the measurement and adjustment system to occasions when adjustment is likely to be necessary, an altitude sensing system is provided and the air/fuel ratio measurement and adjustment system is operated in response to measurement of a change in altitude. Altitude measurement is by way of measurement of absolute pressure in the engine inlet manifold and relating the measured pressure to an expected inlet manifold pressure at sea level for the current conditions of throttle opening and engine speed.

Abstract: The invention is concerned with a control system for an air/fuel ratio measurement and adjustment system for an internal combustion engine. In order to restrict operation of the air/fuel ratio measurement and adjustment system to occasions when adjustment is likely to be necessary, it is desirable to operate the system at approximately daily intervals. The control system incorporates an ambient temperature sensor and an engine coolant temperature sensor and is arranged to operate the measurement and adjustment system when the engine is started if the engine coolant temperature does not exceed the ambient temperature by more than a predetermined amount.