Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation:

SYSTEM DESCRIPTION & OPERATION

The EGR system is controlled by ported vacuum. The EGR system routes exhaust gases from the exhaust manifold to the intake manifold at specified engine operating conditions. The EGR valve is opened to allow exhaust gases to flow into the intake manifold. The exhaust gases combine with the air/fuel mixture in the combustion chamber. Since there is less air/fuel mixture to burn in the combustion chamber, during EGR operation, the temperature is reduced 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, none at idle. The valve should only open when the engine is at operating temperature and above base idle speed. The EGR valve opens under the following conditions:

1. Warm engine operation.
2. Throttle valve off-idle.

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.