Vacuum Operated Type

Fig. 37 Typical EFE valve installation. Vacuum operated type:

The vacuum operated EFE heat control valve mounted between the exhaust manifold and pipe, Fig. 37, directs a portion of the exhaust gases through the intake manifold and to the base of the carburetor during engine warm-up. Some vehicles rely on a thermal vacuum switch (TVS) to control the activation of the EFE valve while others use a solenoid to control the activation function.



Solenoid Controlled Type

This system uses a vacuum actuator controlled by a solenoid. The solenoid controls vacuum to the EFE valve from an electrical signal supplied by the Electronic Control Module (ECM). When engine coolant temperature is below the calibration value programmed into the ECM, the solenoid is energized, increasing the exhaust gas flow under the intake manifold. When engine coolant is above the calibration value, the solenoid is deactivated and vacuum no longer flows to the EFE valve.

Thermal Vacuum Switch Controlled

The thermal vacuum switch is used to regulate the EFE valve at or below a predetermined temperature.
When engine coolant (oil on some engines) is at or below the specified temperature, the TVS will cause vacuum to flow to the EFE control valve, diverting the exhaust gases through the intake manifold to the base of the carburetor. At temperatures above those specified, the TVS closes off vacuum to the EFE control valve, stopping the flow of exhaust gases through the intake manifold. For calibration temperature of thermal vacuum switch, see number stamped at head of switch.