DESCRIPTION
Early Fuel Evaporation (EFE) system is used to provide heat to engine induction system during cold driveaway. The EFE system is vacuum operated exhaust heat riser valve type. The EFE system provides rapid heating, resulting in faster fuel evaporation and more uniform fuel distributor.
OPERATION
Thermal vacuum switch is a normally closed switch which is sensitive to oil (4.8L) or coolant temperature (all other engines). With engine temperature less than 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 greater than 105°F (40°C), thermal vacuum switch opens. This stops vacuum to actuator. Without vacuum, spring pushes actuator diaphragm to rest position and opens EFE valve.
Scheme 186
SYSTEM TESTING
- 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 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. If valve does not stay closed, 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.