The EFE valve, or heat riser, is part of the Early Fuel Evaporation system, described in . It is only used on the 1980 V6 engine. The EFE valve is a thermostatically-controlled, vacuum-operated valve in the right exhaust pipe (near the firewall). It closes when the engine is cold, to direct hot exhaust gases to the intake manifold, in order to preheat the incoming air/fuel mixture. If it sticks open, the result will be frequent stalling during warm-up, especially in cold and damp weather. If it sticks shut, the result will be a rough idle after the engine is warm.
The EFE valve should move freely. It can easily be checked when the engine is cold by pulling the actuating arm next to the vacuum motor to open and shut the valve. If the valve is sticking or binding, a quick shot of solvent especially made for the purpose should free it up. The EFE valve shaft is more easily reached from under the car. The solvent should be applied after the first 6 months or 7,500 miles, and then every 24 months or 30,000 miles thereafter-more often if sticking or binding problems occur.
If the valve is still stuck after application of the solvent, sometimes rapping the end of the shaft lightly with a hammer will break it loose. Otherwise, the components will have to be removed for further repairs.
The 1981 V6 engines continue to utilize the EFE system, but have replaced the valve with an electric heater insulator on the carburetor. There is no periodic maintenance other than replacement.