Evaporative Emissions System: Description and Operation
PURPOSEEvaporative emission system prevents escape of fuel vapors to atmosphere under hot soak and engine off conditions by storing these vapors in an Evaporative Emissions (EVAP) canister. System also controls purging of stored vapors from charcoal canister to engine for burning.
Evaporative Emission System:
OPERATION
System control and operation are accomplished through five separate basic functions in the system:
- Fill control vent system
- Fuel tank vapor venting and storage system
- Evaporative emission purge system
- Evaporative emission return system
- Pressure and vacuum relief system (fuel tank filler cap and fuel tank vent valve).
Evaporative Emission Control System
Fuel is stored in the EVAP canister until it is drawn into the intake manifold and burned when the engine is started. The system is controlled by the Powertrain Control Module (PCM), which operates the Evaporative Emission Canister Purge Valve based on various signals.
Fill Control/Vapor Vent System
Fill is accomplished through the fuel tank filler pipe configuration and a fuel tube attached to the fuel tank filler pipe that extends inside the fuel tank. The vent system is designed to provide an air space above the fuel level in a full tank. The air space allows for thermal expansion of fuel and provides clearance between the fuel level and the evaporative emission valve, that is mounted in the top panel of the fuel tank. The clearance is sufficient to allow vapor venting through the orifice under all static and most dynamic vehicle conditions.
CONSTRUCTION
System consists of a charcoal canister, canister purge solenoid, rollover/vent valve, two-way check valve and a vapor separator.