EGR Electronic Vacuum Regulator Solenoid: Description and Operation

EGR Vacuum Regulator (EVR) Solenoid:

The EGR Vacuum Regulator (EVR) is a single unit electromagnetic device with two vacuum ports. The EVR allows the Electronic Control Assembly (ECA) to modulate the EGR valve opening to any degree, by providing the circuits ground, internally.
The upper port is connected to the vacuum chamber of the EGR valve. The lower port is connected to manifold vacuum or ported vacuum, depending upon system design. Atmospheric pressure is present on one side of the metal disc at all times. This is provided by the vented cover and a hollow electromagnetic core. The disc at the bottom of the core is held in place by a weak spring.
While the EVR is not energized (engine running), a low pressure area develops below the disc from engine vacuum. With this pressure differential, the spring is not strong enough to keep atmospheric pressure from entering the EVR vacuum passages. Vacuum is not applied to the EGR valve diaphragm, thus the EGR valve remains closed.
When the ECA grounds the EVR circuit, a magnetic field is produced from the energized coil. This magnetic field pulls the metal disc against the core's bottom, sealing off the vacuum passages. Engine vacuum is now applied to the EGR valve and the valve opens. The ECA cycles the EVR ON and OFF rapidly in order to control EGR valve opening and therefore exhaust recirculation flow.