Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Early Fuel Evaporation ( EFE ): Description and Operation
Electrically Heated EFE System
Fig. 40 Typical EFE heater grid installation. Electrically heated type
This system uses an electrically heated grid, Fig. 40, to heat air/fuel mixtures during cold engine operation. The grid is located under the primary
throttle bore and is integral with the carburetor insulator assembly. Current flow through the heater grid is controlled by a coolant temperature sensitive
switch on all except models with the C-3 system. On models with C-3, current flow through the heater grid is controlled by the C-3 system computer
through the EFE relay.
On non-ECM controlled models, battery voltage is applied to the EFE temperature switch either through a relay or directly from the ignition feed
circuit. When coolant temperature is below the switch calibration point, the switch is closed and current flows through the heater grid. When coolant
temperature exceeds the switch calibration point, the switch opens and current flow through the grid is stopped.
On models with C-3 system control, battery voltage is applied directly to the heater grid through the EFE relay. Relay operation is controlled by the
ECM based on signals from the C-3 system sensors, allowing the ECM to maintain a more constant intake charge temperature.
