DESCRIPTION
Early Fuel Evaporation (EFE) system is used on General Motors light and heavy duty 4.8L, 5.0L, 5.7L and 7.4L trucks. EFE system is used to provide heat to engine induction system during cold driveaway. EFE system is vacuum operated exhaust heat riser valve type. EFE system provides rapid heating, resulting in faster fuel evaporation and more uniform fuel distribution. This also helps reduce choke "ON" time by warming engine faster.
Scheme 60
Scheme 61
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 and EFE 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.
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.