GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Early Fuel Evaporation (EFE) System

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See Figures 1, 2 and 3

OPERATION



Two types of EFE 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 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. The vacuum type EFE should be checked for proper operation at every tune-up.

On 1981 and later V6 engines, the EFE system is controlled by the ECM.

COMPONENT TESTING

Vacuum type
  1. Locate the EFE valve on the exhaust manifold and not the position of the actuator arm. On some vehicles, the valve and arm are covered by a two-piece cover which must be removed for access. Make sure the engine is overnight cold.
  2.  
  3. 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.
  4.  
  5. If the valve does not close, stop the engine. Remove the hose from the EFE valve and apply 10 in. Hg 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.
  6.  
  7. 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.
  8.  
  9. Warm up the engine to operating temperature.
  10.  
  11. 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.
  12.  



Click image to see an enlarged view

Fig. Fig. 1: Vacuum-servo type EFE system

Electric type
  1. To test the EFE heater, turn the ignition OFF and disconnect the electrical connector.
  2.  
  3. Using an ohmmeter, check the resistance between the two terminals of the heater connector.
  4.  
  5. If resistance is under two ohms, the heater is good. If not, replace the heater.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: Electric-type EFE system

REMOVAL & INSTALLATION



Vacuum type EFE valve

If the vehicle is equipped with an oxygen sensor, it is located near the EFE valve. Use care when removing the EFE valve as not to damage the oxygen sensor.

  1. Disconnect the negative (-) battery cable and vacuum hose at the EFE valve.
  2.  
  3. Remove the exhaust pipe-to-manifold nuts, and the washers and tension springs if used.
  4.  
  5. Lower the exhaust cross-over pipe. On some models, complete removal of the pipe is not necessary.
  6.  
  7. Remove the EFE valve.
  8.  

To install:
  1. Always install new seals and gaskets.
  2.  
  3. Torque the exhaust nuts to 22 ft. lbs. (30 Nm).
  4.  
  5. Connect the negative battery cable and vacuum hose to the valve.
  6.  

Electric type EFE
  1. Remove the air cleaner.
  2.  
  3. Disconnect all vacuum, electrical and fuel connections from the carburetor.
  4.  
  5. Disconnect the EFE heater electrical connector.
  6.  
  7. Remove the carburetor.
  8.  
  9. Remove the EFE heater insulator (plate) assembly.
  10.  
  11. Installation is the reverse of removal.
  12.  

EFE Solenoid
  1. Disconnect the battery ground.
  2.  
  3. Remove the air cleaner assembly if necessary.
  4.  
  5. Disconnect and tag all electrical and vacuum hoses as required.
  6.  
  7. Remove the screw securing the solenoid to the valve cover bracket and remove the solenoid.
  8.  
  9. Installation is reverse of removal.
  10.  

Thermal Vacuum Switch (TVS)
  1. Disconnect the negative (-) battery cable.
  2.  
  3. Remove the air cleaner.
  4.  
  5. Partially drain the engine coolant.
  6.  
  7. Remove the hoses from the TVS assembly located in the engine coolant outlet housing or at the rear of the intake manifold. Remove the switch from the engine.
  8.  

To install:
  1. Refer to the number stamped on the base of the TVS for calibration temperature.
  2.  
  3. Apply a soft setting pipe sealant to the switch threads.
  4.  
  5. Install the switch and torque to 120 inch lbs. (14 Nm). Reconnect the vacuum hoses and negative battery cable.
  6.  
  7. Install the air cleaner assembly.
  8.  



Click image to see an enlarged view

Fig. Fig. 3: TVS switch used on some EFE systems

 
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