Evaporative Emissions System: Description and Operation

Fig. 3 Evaporative System Component Location:

This system consists of a non-vented fuel cap, breather valve, charcoal canister, diaphragm, routing hoses, thermo valve, 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 diaphragm and purge valve.

Fig. 4 Evaporative Hose Routing:

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 50°C (122°F) intake manifold vacuum is applied to the purge valve through the thermo valve. When the vacuum reaches 20-35 mbar (0.7 - 1 in. Hg) the purge valve opens allowing vapors to be extracted from the charcoal canister by the vacuum control bores in the throttle valve.
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.