Reference Manual

Chapter 10: Emissions Equipment: EFE System


The EFE system is used to provide a source of rapid heat to the engine induction system during cold driveaway. Rapid heating is desireable because it provides quick fuel evaporation and more uniform fuel distribution to aid cold driveability.


There are two types of EFE systems: The vacuum servo type and the electrically heated type.

The Vacuum Servo type uses a valve and vacuum actuator which increases the exhaust gas flow under the intake manifold during cold engine operation. The valve is located in the exhaust and is vacuum operated. It is controlled by a Thermal Vacuum Switch (TVS), or an EFE solenoid controlled by the ECM. When vacuum is applied, the valve closes, causing the intake to heat up.

The electrical type of EFE uses a ceramic heater grid located underneath the primary base of the carburetor, as part of the carburetor insulator gasket. When the engine coolant is below a calibrated value, electrical current is supplied to the heater. This is accomplished with an ECM controlled relay.

When the temperature switch or relay turns on, the heater increases temperature and self-regulates at a calibrated temperature, until engine coolant reaches a calibrated value and the circuit opens.

Results of Incorrect EFE Operation:

No EFE when cold:

EFE stays on:

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