DESCRIPTION
Two Early Fuel Evaporation (EFE) systems are used on light and heavy duty trucks. The EFE systems are used to provide heat to the engine induction system during cold driveaway. Engines may be equipped with either an electric heater type (4-cyl.) or a vacuum operated exhaust heat riser valve type (all others) EFE system.
Both the vacuum type and the electric type systems provide rapid heating, resulting in faster fuel evaporation and more uniform fuel distribution. This also helps reduce choke "on" time by warming the engine faster.
EFE System (6-Cylinder Engines) 6-Cylinder engine EFE is controlled by oil temperature. Scheme 80
EFE System (V8 Engines) V8 engine EFE is controlled by water temperature. Scheme 81
4-CYLINDER ENGINES
The electrical heater type system uses a ceramic heater grid under the primary bore of the carburetor as an integral part of the carburetor insulator and gasket. When the engine coolant temperature is below a given value, electrical current is supplied to the heater through a relay.
6-CYLINDER ENGINES
Thermal vacuum switch is a normally closed switch which is sensitive to oil temperature. With a cold engine, below 150°F (66°), 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 oil temperature is above 150°F (66°C), thermal vacuum switch opens. This stops vacuum to actuator. Without vacuum, a spring pushes actuator diaphragm to its at rest position and opens EFE valve.
V8 ENGINES
On V8 engines TVS is located in coolant outlet housing and directly controls vacuum. With coolant temperatures below 180°F (82°C), manifold vacuum is applied to actuator which closes EFE valve. This routes hot exhaust gases to base of carburetor. When temperatures reach 180°F (82°C), vacuum to actuator is stopped. This allows a spring to return actuator to its at rest position, opening EFE valve.
EFE System (4-Cylinder Engines) Heater grid warms incoming fuel mixture. Scheme 82
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 "Neutral" or "PARK" 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 coolant temperature reaches 180°F (82°C) on V8 or oil temperature reaches 150°F (66°C) 6-cylinder engines, 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 temperature below 140°F (60°C), 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.