Evaporative Emissions System: Description and Operation
PurposeThe fuel evaporative emission system allows for controlled release of fuel tank pressure through a evaporative emission canister. Under normal operating conditions, this system will allow sufficient venting to prevent a build-up of internal fuel tank pressure.
Fuel Tank Evaporative Emission System Components
^ fuel tank and fuel tank filler pipe.
^ pressure/vacuum relief fuel tank filler cap.
^ evaporative emission valve with open flow to vacuum and pressure relief.
^ evaporative emission tube and evaporative emission hoses.
^ evaporative emission canister.
Engine Evaporative Emission System Components
^ evaporative emission canister purge valve (CANP).
^ evaporative emission canister. System control and operation are accomplished through separate basic functions in the system:
^ fill control vent system
^ fuel tank evaporative emission venting and storage system
^ evaporative emission purge system
^ fuel tank filler cap and evaporative emission valve
Some operating conditions may cause temporary build-up of internal fuel tank pressure. Some of these conditions are:
^ parking the vehicle after filling the fuel tank on warm or hot days. The fuel is cool from underground storage and vaporizes rapidly when warmed.
^ parking after driving over rough roads, washboard, or other harsh surfaces, after filling the fuel tank. Agitation of fuel increases vaporization.
^ parking after driving long distances in high temperature conditions.
^ climbing long grades, especially while towing a trailer or while vehicle is fully loaded.
No service is required if these conditions caused the customer concern. A normally functioning fuel tank evaporative emission system will relieve the pressure build-up.