Intake Air System

Intake Air System:

The air intake system controls the air required by the engine for operation. The computerized engine control components of the intake air system are the airflow meter and the throttle sensor.
The airflow meter detects the amount of intake air and sends a signal to the engine control unit. The throttle sensor detects the throttle valve opening angle and sends a signal to the engine control unit. The engine control unit uses these signals to decide the amount of fuel to be injected with each engine cycle.
The throttle sensor is a potentiometer splined to the throttle shaft. The potentiometer rotates with the shaft as the throttle plates open and close. The varying resistance of the potentiometer alters the reference voltage emitted from the engine control unit (ECU) and creates a signal for use as input by the ECU.

Fig. 26 Air Flow Meter Inspection:

The airflow meter measures the amount of airflow by connecting a potentiometer to a spring loaded sensor flap. The incoming air passes by the sensor flap, overiding the spring tension to a point of balance, and continues on into the engine. The potentiometer measures the amount of rotation of the sensor flap pivot and alters the reference voltage, thereby creating an input signal for the engine control unit.
Incorporated into the airflow meter is a fuel pump switch and an intake air thermosensor. The fuel pump switch prevents operation of the fuel pump when the engine is not running and the ignition switch is in the "run" position. The intake air thermosensor senses the ambient air temperature and sends a signal to the ECU to allow for fuel compensation due to air density.
The quantity of air necessary for combustion depends on the temperature of the air drawn in. Cold air is denser. This means that with the same throttle-valve position the volumetric efficiency of the cylinders drops as the temperature increases. To register this effect a temperature sensor is fitted in the intake duct of the air-flow sensor. This sensor measures the temperature of the air drawn in and passes this information onto the control unit which then controls the amount of fuel metered to the cylinders accordingly.