Exhaust Gas Recirculation (EGR) System Description
The exhaust gas recirculation (EGR) system is used to reduce the
amount of nitrogen oxide (NOx) emission levels caused by high
combustion temperatures. At temperatures above 1 371°C (2
500°F), oxygen and nitrogen combine to form oxides of nitrogen
(NOX). Introducing small amounts of exhaust gas back into the
combustion chamber displaces the amount of oxygen entering the
engine. With less oxygen in the air/fuel mixture, the combustion
pressures are reduced, and as a result, combustion temperatures are
decreased, restricting the formation of NOX.
Exhaust Gas Recirculation (EGR) System Operation
The EGR valve is vacuum operated. Vacuum for the EGR system is
created by a mechanical pump driven off the camshaft called a
vacuum pump. The EGR solenoid valve is located between the EGR
vacuum pump and the EGR valve. The EGR solenoid valve is powered by
ignition voltage through the main relay. The EGR solenoid valve is
controlled by pulse width modulation signals from the ECM through
the ground circuit allowing the EGR valve to open to the desired
position.
The mass air flow (MAF) sensor signal is used by the engine
control module (ECM) to detect the proper amount of EGR flow. The
ECM will close the EGR valve, then open the EGR valve to 100%. The
ECM will then calculate the MAF difference and determine if the
proper EGR flow has been detected.
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