Early Fuel Evaporation ( EFE ): Description and Operation

Fig. 48 Typical cold mixture heater system:

The electrically operated cold mixture heater is used on some carbureted engines to warm the primary intake manifold runner during cold engine operation. Heating the manifold improves vaporization of liquid fuel, decreasing emissions and improving cold engine driveability. The system consists of an intake mounted heating element, control relay, micro-processor (computer) and thermo switch, Fig. 48.
Battery voltage is supplied to the heating element through the relay, while relay operation is controlled by the system computer. The computer uses thermo switch position and an ``engine running'' signal from the alternator or charging lamp relay to determine engine operating conditions and control relay operation. When the engine is running and coolant temperature is less than 109°F, the computer completes the relay coil circuit, the relay contacts close and voltage is supplied to the heater element. When coolant temperature exceeds 131°F, the computer opens the relay coil circuit, the relay contacts open and the heating element is turned off. If the engine should stall while the heater system is operating, the ``engine running'' signal from the charging system will stop and the computer de-energizes the relay coil circuit.