Evaporative Emissions System: Description and Operation

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

FILL CONTROL/VAPOR VENT SYSTEM
Fill control is accomplished through a vent line attached to the fuel tank filler pipe extending inside the fuel tank. The evaporative emission valve, mounted in the top panel of the fuel tank, and the attached vapor line leading to the Evaporative Emissions (EVAP) canister, also contribute to fill control. These components control the pressure in the fuel tank when the fuel level rises and covers the fill vent opening in the fuel tank.

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

Fuel Vapor Emission Control System (2-Door):

Fuel Vapor Emission Control System (4 Door):

FUEL TANK EVAPORATIVE EMISSION SYSTEM

This system consists of:
- Sealed fuel tank and fuel tank filler pipe.
- Fuel tank filler cap with pressure/vacuum relief.
- Evaporative emission valve with pressure relief and open flow to vacuum.
- Two-way check.
- Evaporative emission separator (2-door models only).
- Evaporative emission tube and evaporative emission hoses.
- Evaporative Emissions (EVAP) canister.
- Evaporative emission canister purge valve.

ENGINE EVAPORATIVE EMISSION SYSTEM

This system consists of:
- Evaporative emission canister purge valve.
- EVAP canister.

The use of these components depends on the calibration of the complete vehicle.

System control and operation are accomplished through five separate basic functions in the system:

1. Fill control venting.
2. Fuel tank vapor venting and storage system.
3. Fuel vapor return system.
4. Fuel vapor purge system.
5. Pressure and vacuum relief system (fuel tank filler cap and evaporative emission valve).