Air traverses the air filter and goes to the air flow sensor. When you open the throttle,
the depression is moving the internal vane of the air flow meter and a bigger amount
of air is sucked in by the engine. The movement of the vanes will turn a variable
resistance. This variable resistance will tell the EFI computer how much gas it has to
send to the injectors to balance the mixture air/fuel.
The volume of air drawn in by the engine reflects the condition of the load. The
precise measurement of this parameter is essential to determine the exact volume of
fuel to inject.
The sensor plate adopts an angular position in relation to the force applied to it by the
air drawn in by the engine
Positioned in the damper chamber, the compensator flap (with the same effective area
as the sensor plate) reduces pulsations due to any back pressure in the inlet manifold.
A temperature sensor is connected in parallel in the air flow sensor electrical circuit.
This is a thermi-resistor and its resistance reduces as the temperature rises. It modifies
the output signal from the air flow sensor in relation to the intake air temperature.
Some air, not taken into account by the sensor plate, pass through the by-pass. By
altering the section of the by-pass, the idling mixture can be altered.
The potentiometer, directly attached to the sensor plate, transmits to the electronic
control unit the voltage corresponding to the angular position of the sensor plate. It is
assembled in dry conditions in a sealed casing. The potentiometer consists of ceramic
plate supporting a contact strip and several resistors whose values have been adjusted
by laser beam. These resistors have the special quality of not varying with the sharp
changes of temperature which occur in the engine compartment. A cursor directly
attached to the sensor plate makes contact with the contact strip.
The battery voltage doesn’t influence the signal from the potentiometer, it is the
relationship between the potentiometer signal and the battery voltage which is taken
into account by the electronic control unit.
The intake air temperature, measured by the temperature sensor, has a direct effect on
the voltage of the potentiometer signal.
Here is what you will find when opening an airflow meter. This one is defective
and the problem comes from pin #5
(The connection with the board is broken and doesn't make contact with the
circuit.)
(5 Seiten)
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