ZEST/BOLT

ENGINE 1.3L QUADRAJET (90PS)

110

1. Electronic circuit cover and measuring duct cover

2. Electronic control circuit

3. Sensitive element with intake air temperature

sensor incorporated

4. Electronic circuit metal support plate and sensitive

element

5. Plastic support casing

NOTE :

The air flow meter cannot be dismantled

PIN OUT

1. 12 V power supply

2. Earth

3. Air temperature signal

4. Air mass signal

OPERATION

The operating principle is based on the heating of a

diaphragm (sensitive element containing two

resistances upstream and downstream of the

support) in a by-pass duct through which the engine

intake air flows.

The hot film membrane is maintained at constant

temperature (about 120 °C higher than the incoming

air temperature) by the specific heating resistance

controlled by the management electronics.

The mass of air passing through the by-pass duct,

giving off heat to the membrane, thermally

unbalances the two resistances to an extent directly

proportional to the mass of the incoming fluid, an

imbalance that is translated through the control circuit

into a resistance variation, electronically processed

and translated into a frequency value to be sent to

the engine management control unit.

The imbalance in the resistance value also makes it

possible to determine the direction of the column of

air.

As far as the air temperature information is

concerned, it is sent to the engine management

control unit via a dedicated pin in the form of a duty

cycle signal (rectangular wave). The value of the duty

is proportional to the value of the temperature.

NOTE :

The flow meter measures the air mass directly (not

the volume) to eliminate problems of compensation

correlated to the temperature, altitude, pressure

values etc.