Evaporative Emissions System: Description and Operation

Evaporative Emission Hose Routing:

This system consists of a non-vented fuel cap, a charcoal canister, a hose circuit connecting the fuel tank to the canister, an electric purge valve, and a hose circuit connecting the purge valve to a calibrated orifice in the engine intake. The fuel vapors from the fuel tank flow to the canister through the hose, where they are absorbed by the activated charcoal. Because of the specific routing of the fuel vapor hoses the need for a fuel tank safety valve has been eliminated.

When the engine is running, the intake vacuum draws the stored canister vapors from the activated charcoal through the calibrated orifice and the electric purge valve located in the hose. The electric purge valve is constantly monitored by the Motronic control unit which opens or closes the valve based on engine operating parameters such as richness, load, temperature, etc. These vapors are then burned in the engine combustion chambers. The vapors will not affect the air/fuel mixture of the engine.