Fuel Evaporation System: Operation
When engine is not running, fuel vapor from fuel tank is directed into charcoal canister for storage. The tank pressure control valve is closed to prevent vapor from escaping into atmosphere. On carbureted models, the vent switching valve is open, allowing fuel vapor from float bowl to enter charcoal canister for storage.
When engine is running, the vent switching valve closes and manifold vacuum opens the tank pressure control valve. This allows fuel vapor from fuel tank and charcoal canister to flow to intake manifold to be burned by the engine. On Sprint, when the engine is running and warmed to normal operating temperature, Bi-metallic Vacuum Switching Valve (BVSV) closes and allows vacuum signal to open purge control valve. With the purge valve open, manifold vacuum draws canister vapor into combustion chambers for burning.
The 2-way check valve is used to balance vapor pressure between fuel tank and canister.