DESCRIPTION
The Early Fuel Evaporation (EFE) is used to provide heat to engine induction system during cold driveaway. Two EFE systems are used. Engines may be equipped with either a vacuum servo type, or an electrically heated type EFE system.
Both vacuum servo and electrically heated systems provide rapid engine warming. Results are faster fuel evaporation, more uniform fuel distribution, faster choke opening and reduced emissions.
VACUUM SERVO TYPE
Vacuum servo type system uses a vacuum operated valve which is controlled by either a Thermal Vacuum Switch (TVS), or by an ECM controlled vacuum solenoid.
During cold engine operation, TVS or vacuum solenoid opens and allows vacuum to close EFE valve. This results in an increase in hot exhaust gas flow under intake manifold.
Vacuum Servo EFE System (Typical). Scheme 40
ELECTRICAL HEATER TYPE
Electrical heater EFE system uses a ceramic heater grid under primary bore of carburetor as an integral part of carburetor insulator and gasket. (Scheme 41)
When engine coolant temperature is below a given value, heater grid is energized by an ECM controlled relay or solenoid, or by a coolant temperature switch.
Electrical Heater EFE System (Typical). Scheme 41
VACUUM SERVO QUICK CHECK
Note. Before performing EFE test, allow engine coolant temperature to cool to below 40°F (4°C).
- Locate EFE valve and note position of actuator arm. On some V8 engines, EFE valve actuator arm is protected by a 2-piece metal cover, which must be removed and then replaced after service has been performed.
- Valve should close when engine is started cold. Actuator link will be pulled into diaphragm housing. If valve does not close, stop engine and remove vacuum hose from EFE valve.
- Using a hand vacuum pump, apply at least 10 in. Hg of vacuum. Valve should close and remain closed for at least 20 seconds without applying additional vacuum. Replace valve if leakdown time is less than 20 seconds.
- If valve does not close, lubricate valve with manifold heat valve lubricant (1050422). Replace valve if necessary. If valve did not close when vacuum was applied and valve is not seized, vacuum diaphragm is defective. Replace EFE valve.
- If valve closed, problem is not in EFE valve. Check for loose, kinked, pinched or plugged vacuum hoses or connections. Also check TVS, vacuum solenoid or relay.
VACUUM SERVO SYSTEM CHECK
For vacuum servo system check, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.
ELECTRICAL HEATER SYSTEM CHECK
For electrical heater system check, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.