See Figure 1
The EFE system is used on the 5.0L (VIN Y) engine to provide a source of quick heat to the engine induction system during cold drive away. The EFE system consists of a vacuum servo (located in the exhaust manifold) and Thermo Vacuum Switch (TVS).
Every 30,000 miles, check the EFE valve (make sure it is free, not sticking), the TVS for proper function and the hoses for cracking or deterioration. If necessary, replace or lubricate.
To check the valve, ensure the engine is cool and move the valve through its full stroke by hand, making sure that the linkage does not bind and is properly connected. Using a hand held vacuum pump, apply 10 in. Hg. of vacuum to valve and verify the vacuum holds and the valve opens. If the valve sticks, free it with a solvent. If the vacuum falls, replace the valve. Also check that all vacuum hoses are properly connected and free of cracks or breaks. Replace hoses or broken or bent linkage parts as necessary.