DESCRIPTION
Two Early Fuel Evaporation (EFE) systems are used on General Motors vehicles. The EFE systems are used to provide heat to the engine induction system during cold driveaway. Engines may be equipped with either the vacuum servo type or the electrical heater type EFE system.
Both the vacuum servo type and the electrical heater type systems provide rapid heating, resulting in faster fuel evaporation and more uniform fuel distribution. This also helps to reduce choke "on" time by warming the engine faster. This helps in reducing exhaust emission levels.
VACUUM SERVO TYPE
The vacuum servo type system uses a vacuum operated valve which is controlled by a thermal vacuum switch (TVS) or a thermal vacuum valve (TVV).
During cold engine operation, the system provides an increase in the exhaust gas flow under the intake manifold. Either the TVS or TVV pass vacuum to the EFE valve when the engine coolant temperature is below the calibration value programmed into the ECM or carried by the TVS or TVV.
Vacuum Servo Type EFE System (Typical). Scheme 55
ELECTRICAL HEATER TYPE
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. (Scheme 56)
When engine coolant temperature is below a given value, electrical current is supplied to the heater through an electrical relay controlled by the ECM.
Electrical Heater Type EFE System (Typical). Scheme 56
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 EFE-TVE, EFE-TVV or EFE solenoids.
VACUUM SERVO SYSTEM CHECK
For Vacuum Servo System Check, see appropriate diagnostic chart in TBI TESTS/CODES article in the ENGINE PERFORMANCE section.
ELECTRICAL HEATER SYSTEM CHECK
For Electrical Heater System Check, see appropriate diagnostic chart in TBI TESTS/CODES article in the ENGINE PERFORMANCE section.