DESCRIPTION
Two Early Fuel Evaporation (EFE) systems are used on General Motors light and heavy duty trucks. EFE systems are used to provide heat to engine induction system during cold driveaway. Engines may be equipped with either electric heater type (4-cylinder and V6) or vacuum operated exhaust heat riser valve type (all others) EFE system.
Both electric and vacuum type systems provide rapid heating, resulting in faster fuel evaporation and more uniform fuel distribution. This also helps reduce choke "ON" time by warming engine faster.
EFE System (6-Cylinder Engines). Scheme 17
EFE System (V8 Engines). Scheme 18
4-CYL. & V6 ENGINES
Electrical heater type system uses ceramic heater grid under primary bore of carburetor as an integral part of carburetor insulator and gasket. When engine coolant temperature is below given value, electrical current is supplied to heater through a relay.
6-CYL. & V8 ENGINES
Thermal vacuum switch is a normally closed switch which is sensitive to oil (6-cylinder) or coolant (V8) temperature. With a cold engine, below 105°F (40°C), TVS is closed which allows manifold vacuum to actuator valve. Vacuum pulls diaphragm in actuator, closing EFE Valve.
This causes hot exhaust gases to be routed to base of carburetor. When engine temperature is above 105°F (40°C), thermal vacuum switch opens. This stops vacuum to actuator. Without vacuum, spring pushes actuator diaphragm to its at rest position and opens EFE valve.
EFE System (4-Cylinder Engines). Scheme 19
MAINTENANCE
Periodically inspect vacuum hoses for damage, actuator for proper operation, linkage for binding and EFE valve for smooth operation.
VACUUM OPERATED TYPE
- With engine cold, position transmission in "N" or "P" and apply parking brake. Start engine and observe movement of actuator rod and exhaust heat valve. Valve should move to its closed position.
- If valve does not close, disconnect hose from actuator and apply 10 in. Hg vacuum to actuator. Valve should close and stay closed for at least 20 seconds. If valve does not stay closed for 20 seconds, replace actuator. Check valve rod and valve for proper operation. Repair as necessary.
- When engine temperature reaches 105°F (40°C), exhaust heat valve should move to open position.
- If valve does not open, disconnect hose at actuator and check for vacuum. If there is vacuum, replace TVS. If no vacuum is present, replace actuator.
ELECTRIC HEATER TYPE
With ignition on, engine off and engine cold, battery voltage should be available at EFE heater. If not, check EFE temperature switch and wiring back to ignition switch and ground. Repair as necessary.