Exhaust Gas Recirculation: Description and Operation

EGR Valve:

EGR Control Solenoid:

SYSTEM DESCRIPTION

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 ported vacuum applied to the top side of the diaphragm. This vacuum must overcome spring pressure in order to open the exhaust gas port. The exhaust gases then blend 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 is called an Electronic Vacuum Regulator Valve (EVRV). 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 EGR opening time.
The ECM uses the information from the the following sensors to enable the EVRV:

1. Throttle Position (TPS)
2. P/N Switch
3. Manifold Absolute Temperature (MAT)

The ECM uses input from the following sensors to regulate the EVRV:

1. Engine Load
2. Coolant Temperature
3. Distributor Speed Signal
4. Torque Converter Clutch (TCC)

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.