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EVAP canister purge valve, carbon filter/ fuel evaporation

EVAP canister purge valve, carbon filter/ fuel evaporation



Carbon filter

The evaporative emission canister is filled with active carbon, which "stores" the fuel vapour coming from the tank until it is exposed of through the purge valve into the intake manifold and used during combustion.

The carbon filter has a hose connection to both the fuel tank and intake manifold but in addition also has a connection to the surrounding air. Via the connection with the surrounding air, the air is drawn in and then passes through the carbon filter taking the fuel vapour into the intake manifold.

EVAP canister purge valve, carbon filter

The EVAP canister purge valve is comprises a solenoid valve, positioned in the vacuum hose between the carbon filter and the intake manifold.

The valve that is controlled by the control module based on information such as engine temperature, speed and load, is opened under specified conditions and lets in the fuel vapour from the coal filter to the intake manifold, where it is burnt together with the normal fuel-/air mixture.

The valve is rubber mounted so that noise is not transferred to the body when the valve is operating.

The EVAP canister purge valve that controls the tank ventilation receives voltage from the main relay and opens when the control module grounds pin 5.

The signal is a square wave at 15 Hz which when idling measures approx. 0.5 volts. When the engine has reached operating temperature the control module opens the purge valve (15Hz) for 1 min. Then the valve closes for 1 min. Soon after that the valve opens for 8 minutes, followed by a 1 minute pause, etc. 8 min. 1 min. 8 min...

When the control module opens the valve, the time the injectors are open is somewhat reduced . The control module compares the lambda sonde signals when the valves are both open and closed so that the values can be adjusted. The control module knows then how much the injection time shall be reduced when the valve is opened.

If an open-circuit occurs or if the connector is turned off the valve is closed.