Evaporative Emissions System: Description and Operation

Evaporative Emission Hose Routing:

This system consists of a non-vented fuel cap, a canister containing activated charcoal, a hose circuit connecting the fuel tank to the canister, a safety valve on the hose circuit, an electric purge valve, a 60°C thermocontact, and a hose linking the canister to a metered jet located on the connecting sleeve after the air flow sensor.

Safety Valve:

When the engine is not operating, fuel vapors from the fuel tank are transmitted through a metered orifice in the safety valve and proceed through the hose circuit to the canister where they are absorbed by the activated charcoal. If the safety valve is tilted more than 45° it will stop the flow of fuel from the fuel tank (roll-over condition).

When the engine temperature is below 60°C the thermocontact, which is subjected to engine coolant, does not allow the electric purge valve to operate, preventing fuel vapors from flowing to the intake system. When the engine temperature is above 60°C the thermocontact opens the electric purge circuit thereby opening the passage of fuel vapors from the canister to the connecting tube behind the air flow sensor.