EGR System: Operation
When the ignition is turned on, power is supplied to both EGR vacuum solenoid valves. The ECA controls operation of these valves by providing a ground circuit to energize the solenoids.
When vehicle is cold, the ECA will energize the No. 1 EGR solenoid valve, causing it to vent vacuum signals to the atmosphere. When engine temperature reaches 140°F (60°C), ECA removes the ground from the No. 1 EGR vacuum solenoid valve and inner spring tension forces the solenoid plunger to close the bleed port.
Vacuum signals are then able to activate the EGR valve. Vacuum signals to this solenoid, however, are modified by 2 other control sources, the No. 2 EGR vacuum solenoid and the EGR modulator valve. See Fig 1 .
The ECA can regulate EGR volume by controlling the ground circuit of the No. 2 EGR vacuum solenoid. When energized, this solenoid allows vacuum to pass through to the EGR vacuum modulator valve.
The modulator valve will allow vacuum to pass through only when sufficient exhaust system backpressure has developed to close the internal bleed hole of the modulator diaphragm. When backpressure has closed the bleed, vacuum signals can then react upon the modulator diaphragm. When the modulator diaphragm rises, vacuum signals from the No. 2 EGR solenoid valve can then pass through the modulator to the No. 1 EGR vacuum solenoid, check valve and EGR valve diaphragm.
California models are also equipped with an EGR Valve Position (EVP) sensor, which sends signals to the ECA based upon EGR valve pintle position. This allows the ECA of California models to more finely regulate EGR action.