Air Flow Meter/Sensor: Description and Operation

Fuel Distributor / Air Flow Sensor:

CONSTRUCTION
Airflow sensor/fuel distributor is made of aluminum and is fitted with a capsule valve. In order not to retard overswing effect during acceleration, capsule valve replaces fixed orifice. Capsule valve opens as soon as control plunger is lifted during acceleration.

Pressure Balance Valve:

Fuel distributor is also fitted with a pressure balance valve.

OPERATION
When throttle valve opens, air energy (PL) forces sensor plate (1) down and control plunger (3) is moved upwards. Fuel above control plunger lifts capsule valve (5). Flow is not directed past orifice (8), but deviates around valve. Movement of components is not slowed down and metering port (4) can open faster and to a greater degree. Pressure pulse inside line leading to control pressure regulator is absorbed by flexible hose connected between fuel distributor and control pressure regulator.

When engine is stopped at operating temperature, fuel heats up and expands. When cooling down, fuel contracts and might cause vacuum to build in control plunger area. Control plunger would be pulled up by vacuum, causing engine to run too rich as soon as it is restarted. To prevent this, a pressure balance valve separating the volume above control plunger and return line has now been fitted. When sustaining pressure drops below .3 bar excess pressure, balance valve opens to prevent vacuum buildup.

Fuel Distributor Connections:

FUEL DISTRIBUTOR CONNECTIONS