4-Cylinder Engines

With coolant temperature below 63°F (17°C), no EGR takes place. The thermo-vacuum valve opens at temperatures above this level. Vacuum is now available for the electric switch-over valve. At idle speeds there is no EGR and switch-over valve is not energized. EGR valve is vented externally.

Starting at speeds of 1300 RPM, the impulses from the TDC transmitter are converted into electrical signals. The switch-over valve is energized and opens. Vacuum arrives at the EGR valve and opens valve. EGR opening is dependent upon engine load. As RPM increases, throttle valve will open and pressure between intake and exhaust manifolds is reduced. As a result, less exhaust gas is drawn into intake manifold.

The vacuum control valve determines amount of vacuum at EGR valve depending on engine load. This amount of vacuum serves as controlling factor for EGR position and shifting of the automatic transmission.

Shortly before full throttle, a lever with a cam switches mechanical switch-over valve to external venting, venting EGR vacuum and eliminating EGR operation.

At speeds above 45 MPH, the impulses transmitted from speedometer impulse transmitter are converted to a control signal. Current to electric switch-over valve is interrupted, EGR is vented, and no further EGR takes place. Individual component operation is described in the following paragraphs