Chevrolet Full Size Cars 1979-1989

Early Fuel Evaporation (EFE) System


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Fig. Fig. 1 View of a common EFE valve mounting between the exhaust manifold and front pipe

This is a more effective form of heat riser (found on earlier vehicles than covered by this guide) and is vacuum actuated. It is used on all carbureted vehicles to heat the incoming fuel/air mixture during the engine warm-up process. It utilizes a ribbed heat exchanger of thin metal that is located in the intake manifold. This pre-heating allows the choke to open more rapidly, thus reducing emissions. Problems with this system might be indicted by poor engine operation during warmup. This valve should be checked initially at 6 months/7,500 miles, and thereafter at 18 months/22,500 mile intervals.

To check the system, move the valve through its full stroke by hand, making sure that the linkage does not bind and is properly connected. If the valve sticks, free it with a solvent. Also check that all vacuum hoses are properly connected and free of cracks or breaks. Replace hoses and broken or bent linkage parts as necessary.