Abstract: An input processing circuit for an air flow sensor comprising a differential amplifier connected through two lines to an air flow sensor and having an operational amplifier an output signal from the air flow sensor and sends a result of this processing to an analogue value - digital value conversion integrated circuit. An output signal from the air flow sensor is supplied to the differential amplifier through a filter circuit so as to prevent an occurrence of error in measuring the amount of sucked air for an internal combustion engine due to various noises. A connection of an inverting input terminal end of the differential amplifier to a ground through a resistor prevents an error caused by a breakage of a reference voltage line connected between the air flow sensor and the input processing circuit. A differential input amplifier circuit also prevents an error caused by a variation in potential resulting from consumption current of an air flow sensor or the like from being generated.

Abstract: A fuel injection control system for an internal combustion engine having means for limiting a fuel amount to be supplied to the engine according to an output of an air flow sensor to a predetermined upper limit value, and means for correcting the intake air flow rate by the output of the air flow sensor when the opening of an intake air throttle valve is opened at a predetermined value, thereby limiting the output of the sensor to the predetermined upper limit value in case that the output of the sensor increases larger than the actual value and correcting the air density if different from a reference by the correcting means.