Self-diagnosis of air-fuel mixture for motor vehicle IC engine

摘要

A device for self-diagnosis of the air-fuel mixture in an IC engine uses an exhaust gas sensor measuring the air-fuel content. Another sensor detects any change in the fuel flow to the engine. A control unit evaluates the rate of change of this second signal and the presence of any abnormality in the sensor from this rate of change of signal. In connection with the change in fuel flow, the control unit detects if either fuel switch-off has begun or if fuel delivery has begun again after switch-off. The rate of change of signal is found from the time period between when the flow rate changes to when it has changed by a preset value.