Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation:

EGR Valve:

SYSTEM DESCRIPTION

The EGR system routes exhaust gases from the exhaust manifold to the intake manifold at specified engine operating conditions. The port EGR valve is controlled by a flexible diaphragm. Ported vacuum is applied to the top side of the diaphragm. This vacuum must overcome spring pressure in order to open the exhaust gas port. The exhaust gas then combines 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 and NOx formation is limited. 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.

EGR Control Solenoid:

EGR CONTROL

The EGR is controlled by a vacuum solenoid that uses "Pulse Width Modulation". The valve allows the ECM to turn ON and OFF the solenoid many times a second, and it varies the amount of ON time (Pulse Width) to change the amount of exhaust gas flow.
The ECM uses the information from the the following sensors to regulate the solenoid:

1. Throttle Position (TPS)
2. Coolant Temperature
3. Mass Air Flow (MAF)

EGR Valve Identification:

EGR VALVE IDENTIFICATION

1. Negative backpressure EGR valves will be stamped with a "N" on the top side of the valve after the part number.
2. Positive backpressure EGR valves will be stamped with a "P" on the top side of the valve after the part number.
3. Port EGR valves will not have any identification stamped on the valve after the part number.