Exhaust Gas Recirculation: Description and Operation

Port EGR Valve:

The EGR system routes exhaust gases from the exhaust manifold to the intake manifold at specified engine operating conditions. The EGR valve is opened by manifold vacuum to let exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. Since there is less air/fuel mixture to burn in the combustion chamber during EGR operation, the temperature is reduced enough to limit NOx formation. If too much exhaust gas enters combustion will not occur. Because of this very, little exhaust gas is allowed to pass through the valve, especially at idle. the valve should only open when the engine is at operating temperature and above idle speed. The EGR vacuum control solenoid and variations in vacuum control the amount of exhaust gas recirculation.

EGR CONTROL
To regulate EGR flow, an ECM controlled solenoid is used in the vacuum line. The ECM uses the Coolant Temperature, Throttle Position and Mass Air Flow sensors for input to regulate the solenoid. The EGR vacuum control has a vacuum solenoid that uses pulse width modulation. What this means is that the ECM turns the solenoid ON and OFF many times a second and varies the amount of ON time (pulse width) to vary the amount of EGR. A diagnostic switch, on some models, is part of the control and monitors vacuum to the EGR valve. This switch will trigger a "Service Engine Soon" light and set a code 32 in the event of a vacuum circuit failure.

EGR Valve Identification:

Port EGR valves have no identification stamped after the part number.