EGR Backpressure Transducer: Description and Operation

PURPOSE
The exhaust gas recirculation (EGR) vacuum modulator serves to regulate the amount of vacuum signal that the EGR valve receives.

OPERATION

EGR System Operation:

When the throttle plate is positioned between port E and port R, the engine speed is below 4000 rpm, the engine coolant temperature is above 53° C (127° F) and the EGR vacuum switching valve is ON, exhaust gas pressure causes the atmospheric passage inside the EGR vacuum modulator to CLOSE and allows the vacuum signal from port E to be passed to the EGR valve. This causes the exhaust pressure to drop, which allows the vacuum modulator to OPEN, stopping the vacuum signal to the EGR valve. When the EGR valve closes the exhaust gas pressure again increases, closing the atmospheric passage inside vacuum modulator to CLOSE and passing the vacuum signal to the EGR valve. This cycle continues as long as conditions remain within a predetermined range.
When the throttle plate is positioned above port R, the vacuum modulator CLOSES the atmospheric passage and increases the opening of the EGR valve even if exhaust gas pressure is high.