Air Flow Meter/Sensor: Description and Operation

BASIC FUNCTION

Air Flow Sensor - Basic Fuel Metering:

The air flow sensor is an integral part of the fuel distributor, and the primary controller of the fuel delivery rate. Basic fuel delivery is mechanical/hydraulic controlled. The air flow sensor plate is attached to a counter ballanced lever arm which operates a plunger (control plunger) in the fuel distributor. The control plunger varies the cross-sectional area of a small slit (one for each cylinder) which fuel passes through (@ constant pressure drop) to the injectors. The more air that is drawn into the engine, the more the sensor plate is deflected, lifting the control plunger which enlarges the open area of the metering slit, allowing more fuel to flow to the injectors. For more detailed information on the mechanical/hydraulic operation of the air flow sensor and fuel distributor, refer to FUEL SUPPLY AND AIR INDUCTION.


ELECTRONIC MONITORING - SENSOR PLATE POTENTIOMETER

Air Flow Sensor Potentiometer:

Fuel enrichment, ignition timing, and dwell are adjusted according to points on complex "maps" (multi-dimensional graphs) programmed into the computer memories. Engine load is a factor in locating these points. The air flow sensor position is monitored by both fuel control and ignition control ECUs, to help determine the engine load. A potentiometer is attached to the sensor arm. As the sensor plate is deflected by intake air, the resistance through the potentiometer changes, causing a proportional change in the circuit voltage. Each voltage value corresponds to a definite position of the sensor plate, and a specific volume per unit time of air. The control units calculate the volume of air the engine is consuming, and compare this with the engine displacement and rpm to determine the engine load.