Exhaust Gas Recirculation: Description and Operation

Fig. 11 EGR Components:

The EGR valve is controlled by the ECM through the EGR solenoid and by exhaust back pressure acting on the Back-Pressure Transducer (BPT) Valve.
Vacuum is allowed to the EGR valve on acceleration and shut OFF upon deceleration or idling. The diaphragm mounted in the BPT valve raises in relation to exhaust pressure, opening an orifice allowing vacuum to be applied to the EGR Valve in response to the throttle opening.
Only when the following conditions are met does the ECU energize the solenoid which redirects vacuum from the source port and valve port to the source port and vent port preventing the EGR valve from operating:
^Engine starting.
^Engine speed over 2700 RPM.
^Low coolant temperature.
^High coolant temperature.
The amount of vacuum allowed to the EGR valve is directly dependent on the throttle valve opening, the amount of ported vacuum being generated at the time and the exhaust gas back-pressure.