High Speed EGR Modulator

Fig.47 - High Speed EGR Modulator:

The high speed EGR modulator sub-system used on some V-8 engines, Fig. 47, is basically the same in operation as the ESC system described previously. This system cuts off exhaust gas recirculation flow by stopping vacuum flow from the EGR port to the EGR valve at speeds above 64 mph, in turn improving driveability.

The vacuum solenoid valve installed in the vacuum line is normally open (not energized), allowing vacuum flow from the EGR port to the EGR valve. The EGR system remains functional when the valve is not energized.

The speed sensor driven by the speedometer cable, produces an electric signal directly proportional to vehicle road speed, signaling the amplifier to energize the vacuum solenoid valve at which time the electronic module receives the signal from the speed sensor and amplifies it to provide a usable signal to the vacuum solenoid valve.

When the vehicle speed exceeds approximately 64 mph (trigger speed of the amplifier) the circuit to the ignition switch is completed and the normally open vacuum solenoid valve is energized. The plunger moves upwards and shuts off the EGR port vacuum and the vent at the bottom of the vacuum valve is opened, bleeding vacuum from the EGR valve and hose. Spring force closes the EGR valve which remains nonfunctional until the vacuum solenoid valve is de-energized, at speeds below approximately 64 mph.


NOTE: There is a continuous internal vacuum bleed provided by the vent at the top of EGR valve. Whether the valve is in a closed or open position, this vent purges the vacuum supply hose from the carburetor of any gasoline vapor.