B Series Truck 4WD L4-2606cc 2.6L SOHC (1992)
Mass Air Flow Sensor: Description and Operation
Air Flow Meter/Sensor
Air Intake System
^ A hot wire type mass Airflow Sensor is utilized to measure the volume of air entering the intake system. Unlike a flap type air flow sensor which
only measures the volume of air flow, a mass air flow sensor measures the actual mass per unit time of air entering the engine. This is a more
accurate measurement because any given volume contains different quantities of air depending on the air density.
^ The sensor converts the amount of air taken into the engine into an electric signal by using the heat transfer phenomenon between incoming air and a
heated resistor (wire). The ECU uses this information, together with input data from other sensors, to calculate fuel injector pulse ("ON" time) and
thus regulate air/fuel ratio.
^ A platinum wire filament located in the intake air flow is heated by electric current. The flow of intake air cools the wire, causing a decrease in
resistance. As this occurs, more current is required to maintain the ECU programmed reference temperature. At idle, very little air passes over the
wire and the cooling effect is small. Resistance through the wire is high and very little additional current is required to maintain its temperature. As
the throttle is opened and the air flow over the hot wire increases, the cooling effect also increases, requiring more current to maintain its
temperature. The ECU measures the current through the wire and uses this information to calculate the mass of air entering the engine.
