Chevrolet Chevette/1000 1976-1988 Repair Guide

Early Fuel Evaporation System (EFE)

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OPERATION





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Fig. Fig. 1The Early Fuel Evaporation (EFE) heater is located under the carburetor



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Fig. Fig. 2After the carburetor is removed, you can lift the EFE heater grid from the studs to remove it

The electric EFE system utilizes a ceramic heater grid located underneath the primary bore of the carburetor as part of the carburetor insulator gasket. It heads the incoming fuel-air charge for improved vaporization and driveability on cold drive-way.

On 1980 models, when the ignition switch is turned on, voltage is applied to a snap action bimetal switch. If engine coolant temperature is below calibrated value, a circuit is completed to the heater and current begins to flow. The heater, incorporating a Positive Temperature Coefficient (PTC) semiconductor element, increases in temperature and then self-regulates at a calibrated temperature, except at high engine speeds when the fuel-air flow will reduce the temperature below the regulated value. When coolant temperature reaches the calibrated value, the snap action switch breaks the circuit and shuts off the heater.

On 1981 and later models when the ignition switch is turned ON and engine coolant temperature is low, voltage is applied to the EFE relay through the ECM. With the EFE relay energized, voltage is applied to the EFE heater. When coolant temperature increased, the ECM de-energizes the relay which shuts off EFE heater.

 
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