Exhaust Gas Recirculation (EGR) System Description. Chevrolet Tracker

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2002 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.5L (LE8) 🢒 Exhaust Gas Recirculation (EGR) System Description

The exhaust gas recirculation (EGR) system controls the formation of oxides of nitrogen (NOx) emissions by recirculating the exhaust gases into the combustion chamber. NOx emissions increase with combustion chamber temperatures. Controlling the high combustion chamber temperatures will help limit the formation of NOx emissions. The EGR system accomplishes this by admitting controlled amounts of exhaust gas into the intake manifold to mix with the incoming air. Mixing exhaust gases with incoming air/fuel mixture modifies the combustion process resulting in lower combustion chamber temperatures.

EGR Valve


(1)	Plunger Spring
(2)	Plunger Valve
(3)	Exhaust Gas Flow
(4)	Plunger Shaft
(5)	Plunger (Threaded End)
(6)	Stepper Motor

The EGR valve is a stepper motor design. A stepper motor (6) drives a worm gear, that is in mesh with a spring (1) loaded plunger (5). The valve (2) end of the plunger (4) controls the flow of exhaust gases (3). The plunger movement is controlled by the powertrain control module (PCM). By turning the stepper motor in different directions, the PCM controls the opening of the exhaust gas passage to the intake manifold.

Operation

The PCM uses the inputs from various sensors in order to control the operation of the EGR valve. Information from the engine coolant temperature (ECT) sensor, the throttle position (TP) sensor, the vehicle speed sensor (VSS), and the manifold absolute pressure (MAP) sensor are critical for proper EGR valve operation. Under heavy engine loads, when the demand for power is high, the EGR valve is closed. In order to insure a smooth idle and stable engine operation, the EGR valve is also closed at closed throttle engine operation. The EGR valve is usually open during low and medium engine loads and speeds. Combining pre-programmed engine calibrations with various sensor inputs, the PCM calculates the optimum opening of the EGR valve.

Results Of Incorrect Operation of the EGR System

Excessive EGR valve flow may cause any of the following conditions:

•	The engine stalling

•	Rough idle, surging, or engine hesitation

•	Lower fuel economy

•	Incomplete combustion and high exhaust emissions

Inadequate EGR valve flow may cause any of the following conditions:

•	Engine detonation

•	Excessive exhaust emissions