Two types of EFE have been used on the engines covered in this guide. Both provide quick heat to the induction system, which helps evaporate fuel (reducing emissions) when the engine is cold and aids cold driveability. The Vacuum Servo EFE system uses a valve between the exhaust manifold and exhaust pipe, operated by vacuum and controlled by either a thermal vacuum valve or electric solenoid. The valve causes hot exhaust gas to enter the intake manifold heat riser passages, heating the incoming fuel mixture. The Heated-type EFE uses a ceramic heater plate located under the carburetor, controlled through the ECM. The vacuum-type EFE should be checked for proper operation at every tune-up.
On 1981 and later V6 engines, the EFE system