Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation:

Negative Backpressure EGR Valve:

SYSTEM DESCRIPTION
The EGR system routes exhaust gases from the exhaust manifold to the intake manifold at specified engine operating conditions. This EGR valve is called a negative backpressure valve. It varies the amount of exhaust gases flowing into the intake manifold depending upon the manifold vacuum, and variations in exhaust backpressure. The amount of vacuum to the EGR valve is controlled by the ECM, which triggers a solenoid. The exhaust gases combine 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
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 EGR diagnostic temperature switch monitors the temperature of the air flowing past the EGR valve. During cold operation and at idle, the solenoid is not grounded by the ECM, and vacuum to the EGR is blocked.

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.