Evaporative Emissions System: Description

An Early Fuel Evaporation (EFE) system is used on all Light Duty and some Heavy Duty Emission models. System provides improved cold driveability while reducing exhaust emissions.

Fig 1: General Motors EFE System for 6-Cylinder Engines

Courtesy of GENERAL MOTORS COMPANY

6-Cylinder engine EFE is controlled by oil temperature. 

System consists of an EFE valve, an actuator and a thermal vacuum switch (TVS). The TVS is coolant temperature controlled on V8 engines and oil temperature controlled on 6-cylinder engines.

Fig 2: General Motors EFE System for 5.0L & 5.7L V8 Engines

Courtesy of GENERAL MOTORS COMPANY

V8 engine EFE is controlled by water temperature.