Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation:

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 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, none at idle, wide open throttle, or during high engine load conditions. The valve should only open when the engine is at operating temperature and above base idle speed. The amount of exhaust gas flow is controlled by variations in engine vacuum and exhaust back pressure.

Negative Back Pressure EGR Valve:

EGR CONTROL

The EGR valve used on this engine is a negative back pressure valve. The amount of exhaust gas flow depends on manifold vacuum and variations in exhaust back pressure. The valve has an internal vacuum bleed hole which is forced closed by a small spring when no exhaust back pressure is present. Vacuum opens the EGR valve against the pressure of a large spring. When manifold vacuum combines with exhaust back pressure, the vacuum bleed hole opens and the EGR valve closes.

NOTE: The EGR valve will open if vacuum is applied to the valve with the engine not running.

EGR Valve Identification:

EGR VALVE IDENTIFICATION

Negative back pressure EGR valves will be stamped with a "N" on the top side of the valve after the part number.