GM Firebird 1967-1981 Repair Guide

Early Fuel Evaporation System (EFE)

Print

See Figures 1, 2, 3 and 4

Click image to see an enlarged view

Fig. Fig. 1: Early Fuel Evaporation (EFE) system heat valve and power actuator mounting locations 1975-81 8-cylinder engines



Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the vacuum-controlled EFE valve mounting



Click image to see an enlarged view

Fig. Fig. 3: EFE valve and actuator location on the 231 V6 engine



Click image to see an enlarged view

Fig. Fig. 4: The EFE remote actuator is mounted on the right exhaust manifold, and is easily removed, if needed

The EFE system is used only on 1975-81 models

1975 and later models are equipped with this system to reduce engine warm-up time, improve driveability, and reduce emissions. On start-up, a vacuum motor acts to close a heat valve in the exhaust manifold which causes exhaust gases to enter the intake manifold heat riser passages. Incoming fuel mixture is then heated and more complete fuel evaporation is provided during warm-up.

The system consists of a Thermal Vacuum Switch, and an Exhaust Heat Valve and actuator. The Thermal Vacuum Switch is located on the coolant outlet housing on V8s, and on the block on in-line six cylinder engines. When the engine is cold, the TVS conducts manifold to the actuator to close the valve. When engine coolant or, on 6-cylinder engines, oil warms up, vacuum is interrupted and the actuator should open the valve.

On 1981 models with the 231 V6 engine, the EFE system is controlled by the ECM.

Some 1981 engines utilize an electrically heated EFE system. Although the function of this system remains the same to reduce engine warm-up time, improve driveability and to reduce emissions the operation is entirely different. This system is electric and uses a ceramic heater grid located underneath the primary bore of the carburetor as part of the carburetor insulator/gasket. When the engine coolant is below the specified calibration level, electrical current is supplied to the heater through an ECM-controlled relay.

CHECKING THE EFE SYSTEM



  1. With the engine overnight cold, have someone start the engine while you observe the Exhaust Heat Valve. The valve should snap to the closed position.
  2.  
  3. Watch the valve as the engine warms up. By the time coolant starts circulating through the radiator (V type engines) or oil is hot (in line engines), the valve should snap open.
  4.  
  5. If the valve does not close, immediately disconnect the hose at the actuator, and check for vacuum by placing your finger over the end of the hose, or with a vacuum gauge. If there is vacuum, replace the actuator. If there is no vacuum, immediately disconnect the hose leading to the TVS from the manifold at the TVS. If there is vacuum here, but not at the actuator, replace the TVS. If vacuum does not exist at the hose going to the TVS, check that the vacuum hose is free of cracks or breaks and tightly connected at the manifold, and that the manifold port is clear.
  6.  
  7. If the valve does not open when the engine coolant or oil warms up, disconnect the hose at the actuator, and check for vacuum by placing your finger over the end of the hose or using a vacuum gauge. If there is vacuum, replace the TVS. If there is no vacuum, replace the actuator.
  8.  

REMOVAL & INSTALLATION Thermal Vacuum Switch



On V8 engines, drain coolant until the level is below the coolant outlet housing. No oil need be drained on 6-cylinder engines. Apply sealer to threads on V8 engines. Use no sealer on 6-cylinder engines. Note that the valve must be installed until just snug (120 inch lbs.) and then turned by hand just far enough to line up the fittings for hose connection.

EFE Heater

  1. Remove the air cleaner.
  2.  
  3. Disconnect all electrical, vacuum and fuel connections from the carburetor.
  4.  
  5. Disconnect the EFE heater electrical connection.
  6.  
  7. Remove the carburetor as detailed later in this section.
  8.  
  9. Lift off the EFE heater.
  10.  
  11. Installation is in the reverse order of removal.
  12.  
  13. Start the engine and check for any fuel leaks.
  14.  

EFE Heater Relay See Figure 5

Click image to see an enlarged view

Fig. Fig. 5: Some 1981 models utilize an electrical EFE heater, which is mounted between the carburetor and the plenum

  1. Disconnect the negative battery cable.
  2.  
  3. Tag and disconnect all electrical connections.
  4.  
  5. Unscrew the retaining bolts and remove the relay.
  6.  
  7. Installation is in the reverse order of removal.
  8.  

 
label.common.footer.alt.autozoneLogo