Evaporative Emission Control Canister: Description and Operation

Fig. 85 EVAP Diagram:

This system consists of a non-vented fuel cap, breather valve, charcoal canister, switchover valve, routing hoses, and purge valve. The canister contains activated charcoal and is mounted behind the left front wheel housing panel. A hose connects the charcoal canister to the throttle valve via the purge valve.
When pressure in the fuel tank reaches 30-50 mbar (0.435 - 0.725 psi.) the breather valve opens allowing fuel vapors to flow from the fuel tank to the charcoal canister where they are absorbed.
With the engine running at a coolant temperature above 80° C (175°F) and the idle speed contact on the throttle valve open the switchover valve applies vacuum from the intake manifold to the purge valve. Thus, the purge valve opens allowing fuel vapor from the charcoal canister to be drawn into the intake manifold via a port in the throttle plate. At a coolant temperature of greater than 100° C (212° F) or intake temperatures of greater than 55° C (130 ° F), and a vehicle speed of less than 3 miles mph purging takes places even with the idle contact closed.
When a vacuum of 1-16 mbar (.062 - .45 in. Hg) is reached in the fuel tank the breather valve opens drawing air through the diaphragm and fuel vapors from the canister to flow to the fuel tank.