EGR Valve: Description and Operation

Fig. 18 EGR valve with integral back-pressure sensor:

Fig. 19 EGR valve without integral back-pressure sensor:

The EGR valve, Figs. 18 and 19, is mounted on a machined surface at the rear of the intake manifold on V8 engines, on the side of the intake manifold on six cylinder engines and on a space-plate beneath the carburetor on four cylinder engines. The valve used with an automatic transmission is calibrated differently than the valve used with a manual transmission.

The valve is held in a normally closed position by a coiled spring located above the diaphragm. A special fitting is provided at the carburetor to route ported (above throttle) vacuum through hose connections to a fitting on the valve which is located above the diaphragm.

A passage in the intake manifold directs exhaust gas from the exhaust crossover passage or from below the riser area to the EGR valve. When the diaphragm is actuated by vacuum, the valve opens and meters exhaust gas through another passage in the intake manifold to the floor of the manifold below the carburetor.