200 Quattro 20V Sedan L5-2226cc 2.22L DOHC Turbo (3B) (1991)
Evaporative Ventilation System
This system prevents fuel vapors from entering the atmosphere. The fuel vapors are stored in the charcoal canister while the engine is OFF. The canister
is located on the right side of the vehicle in front of the "A" pillar. When the engine is started, the charcoal canister frequency valve opens, which allows
the vapors to be drawn into the intake manifold to be burned during normal combustion.
FREQUENCY VALVE
The frequency valve, located behind the engine between the cylinder head and the firewall, is controlled by the Fuel Injection control unit. It regulates
the flow of fuel vapors from the charcoal canister. The valve's duty cycle will vary from 0 - 100% depending on engine temperature, load and speed. A
check valve within the frequency valve closes when the engine is shut off, this keeps the fuel vapors from entering the intake manifold. If the frequency
valve should fail, vacuum from the intake manifold will open the check valve and allow a calibrated amount of vapors to enter the intake manifold.
ROLL OVER VALVE
The roll-over (vent) valve is integral with fuel level sender, located on top of the fuel tank.