Evaporative Emissions System: Description and Operation

Typical System:

As part of the fuel system, an evaporative emission system is used to meet federal requirements in effect at the time of production.

FILL CONTROL/VAPOR VENT SYSTEM
Fill control is accomplished through a vent baffle integral to the fuel tank filler pipe, which extends inside the fuel tank. As the fuel level rises to cover the fill vent, pressure rises in the fuel tank causing fuel to back up and shut off the fuel dispensing nozzle.

The vent system is designed to provide an air space, approximately 10 percent of the fuel tank volume, above the fuel level in a full fuel tank. The air space allows for thermal expansion of fuel and provides clearance between the fuel level, the vapor orifice, and the evaporative emission valve. The clearance is sufficient to allow vapor venting through the orifice under all static and most dynamic vehicle conditions.

THE FUEL TANK EVAPORATIVE EMISSION SYSTEM CONSISTS OF:
- Fuel tank filler cap
- Evaporative emission valve

THE ENGINE EVAPORATIVE EMISSION SYSTEM CONSISTS OF:
- Evaporative emission hoses
- Evaporative emissions canister
- Evaporative emission tube shut off valve
- Evaporative emission canister purge valve