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What is a Mass Airflow Sensor?
A mass airflow sensor is a device used in fuel injected engines to measure the mass, amount or weight of air passing through it. They are placed on the intakes which deliver air into the engine's combustion chambers. This device is used by the electronic engine control unit to determine how much fuel should be delivered to the combustion chambers via the fuel injectors in order to maintain the best air/fuel ratio for combustion. There are two types of mass airflow sensor: the vane meter sensor and the hot wire sensor.
How Does a Vane Meter Sensor Work?
A vane meter sensor has a spring-loaded paddle which extends into the air stream of the intake. The vane is pushed back in proportion with the strength of the airflow, creating a potential charge in proportion to the degree with which the vane is being pushed. This charge is sent to the engine control unit and registered, the strength of the charge telling the ECU the volume of airflow. The primary drawback to this type of sensor is that the paddle itself can restrict airflow, decreasing engine output.
How Does a Hot Wire Sensor Work?
A hot wire sensor works by passing an electrical current through a wire suspended in the engine's air stream, heating it. As the temperature increases, the wire's electrical resistance increases, limiting the amount of electrical current which can flow through the circuit attached to the wire. As air intake increases, the passing air cools the wire, decreasing its resistance and increasing the amount of electricity passing through the circuit. The wire's temperature is set to maintain equilibrium with the passing air, so the current increases only when the air intake increases. Likewise, the current decreases when the air intake decreases from the norm. These changes in current flow are registered by the engine control unit and translated into the relevant information for the ECU to make the necessary changes to account for the new intake level. These types of sensors are very accurate, however they are fragile. Any dirt or oil can contaminate the wire and cause an inaccurate reading, if not causing the wire to catch fire.