Evaporative Emissions System: Description and Operation

Evaporative Canister And Purge Valve:

This system consists of a non-vented fuel cap, a canister with incorporated purge valve containing activated charcoal located on the left inner wheel well, a hose circuit connecting the fuel tank to the canister, a safety valve on the hose circuit, and a hose linking the canister to a metered jet located on the connecting sleeve after the air flow sensor.

When the engine is not operating, fuel vapors from the fuel tank are transmitted through a metered orifice in the one-way 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 is running a purge control vacuum signal which is taken from downstream of the throttle plate acts upon the canister purge valve. At engine idle a small amount of purge vapor flows through the constant purge hole in the canister valve. When the throttle opens, the vacuum to the air valve allows full canister purge at a controlled rate.