Two types of EFE systems have been used on the engines covered in this guide. Both provide quick heat to the induction system. This helps evaporate fuel (allowing the choke to close faster and thus reducing emissions) when the engine is cold. It also aids cold driveability.
The vacuum servo EFE system uses a valve between the exhaust manifold and exhaust pipe, operated by vacuum and controlled by either a thermal vacuum valve or electric solenoid.The vacuum type EFE should be checked for proper operation at every tune-up. The valve causes hot exhaust gas to enter the intake manifold heat riser passages, heating the incoming fuel mixture.
The electrically heated type EFE uses a ceramic heater plate located under the carburetor, controlled through the ECM.
On 1981 and later V6 engines, the EFE system is controlled by the ECM.
See Figures 1 and 2Vacuum Type
- Locate the EFE valve on the exhaust manifold and note the position of the actuator arm. On some vehicles, the valve and arm are shielded by a two-piece cover which must be removed for access. Make sure the engine is overnight cold.
- Watch the actuator arm when the engine is started. The valve should close when the engine is started cold; the actuator link will be pulled into the diaphragm housing.
- If the valve does not close, stop the engine. Remove the hose from the EFE valve and apply 10 in. Hg (69 kPa) of vacuum by hand pump. The valve should close and stay closed for at least 20 seconds (you will hear it close). If the valve opens in less than 20 seconds, replace it. The valve could also be seized if it does not close; lubricate it with spray type manifold heat valve lube. If the valve does not close when vacuum is applied and when it is lubricated, replace the valve.
- If the valve closes, the problem is not with the valve. Check for loose, cracked, pinched or plugged hoses, and replace as necessary. Test the EFE solenoid (located on the valve cover bracket); if it is working, the solenoid plunger will emit a noise when the current is applied.
- Warm up the engine to operating temperature.
- Watch the EFE valve to see if it has opened. It should now be open. If the valve is still closed, replace the solenoid if faulty, and/or check the engine thermostat; the engine coolant may not be reaching normal operating temperature.
- To test the EFE heater, turn the ignition OFF and disengage the electrical connector.
- Using an ohmmeter, check the resistance between the two terminals of the heater connector.
- If resistance is under 2 -, the heater is good. If not, replace the heater.