Exhaust Gas Recirculation: Description and Operation

SYSTEM DESCRIPTION

EGR System Diagram:

The EGR system is used to reduce Oxides of Nitrogen (NOx) emissions. Oxygen and Nitrogen do not normally combine except at very high temperatures and pressures, conditions which are present in the combustion chamber, especially during hard acceleration. When the engine is under load, the EGR valve admits a small amount of exhaust gas into the air/fuel charge. The exhaust gas is essentially inert (contains no fuel or oxidizer) and reduces peak combustion temperatures and pressures by absorbing some of the heat of combustion without participating in the actual burn. Greater amounts of exhaust gas are metered in as engine speed and load are increased.

EGR VALVE

The EGR valve meters exhaust gas into the intake system. The EGR valve is normally closed. When the system is operating, ported vacuum is applied to the diaphragm chamber of the EGR valve, opening the valve during acceleration and cruising conditions.

EGR FREQUENCY VALVE

EGR Frequency Valve V8:

A solenoid operated vacuum switching valve is used to regulate the vacuum signal to the EGR valve. The valve is computer operated and works on a duty cycle signal ("ON" time vs. "OFF" time). The valve gets battery power when the ignition is turned "ON" and is energized when the ECM completes the circuit to ground. When the engine reaches normal operating temperature, the ECM begins cycling the solenoid, allowing the EGR system to operate.