Exhaust Gas Recirculation: Description and Operation

PURPOSE
The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by reducing combustion temperatures.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With fuel/air mixture thus diluted, combustion temperatures are reduced.

OPERATION
The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust tot the intake manifold through an orifice with a PCM controlled pintle. During operation, the Powertrain Control Module (PCM) controls pintle position by monitoring the pintle position feedback signal.

The feedback signal can be monitored with a Tech 1 as "Actual EGR Pos" which should always be near the commanded EGR position.

The linear EGR valve is usually activated under the following conditions:

^ Warm engine operation.
^ Above idle speed.

Linear EGR Control
The PCM monitors EGR position and adjusts pintle position accordingly. The PCM uses information from the following sensors to control the pintle position:

^ Engine Coolant Temperature (ECT) sensor.
^ Throttle Position (TP) sensor.
^ Mass Air Flow (MAF).