Exhaust Gas Recirculation: Description and Operation
EGR SYSTEM COMPONENTSEGR System Description
- The Exhaust Gas Recirculation (EGR) system controls the oxides of nitrogen (NOx) emissions. To lower NOx emissions, the temperature in the combustion chamber must be decreased. This is accomplished by recirculating small amounts of exhaust gases back into the combustion chamber to mix with the air/fuel charge.
- The 2.3 L engine incorporates a stepper motor controlled EGR valve which receives its signal from the PCM. Engine coolant is used to cool the EGR valve. The EGR valve and stepper motor are serviced as an assembly.
1. EGR System Operation
- The Differential Pressure Feedback EGR system receives signals from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) sensor, Mass Air Flow (MAF) sensor and Crankshaft Position (CKP) sensor to provide information on engine operating conditions to the PCM. The engine must be at normal operating temperature, stable and running at a moderate load and rpm before the EGR system is activated. The PCM deactivates the EGR during idle, extended wide open throttle or whenever a failure is detected in an EGR component or EGR required input.
2. PCM
- Calculates the desired amount of EGR flow for a given engine condition. It then determines the desired pressure drop across the metering orifice required to achieve that flow and outputs the corresponding signal to the EGR vacuum regulator solenoid.
3. EGR Vacuum Regulator Solenoid
- Receives a variable duty cycle signal (0 - 100%) from the PCM. The higher the duty cycle, the more vacuum the solenoid diverts to the EGR valve.
4. EGR Valve
- Increases or decreases the flow of exhaust gas recirculation. As vacuum applied to the EGR valve diaphragm overcomes the spring force, the valve begins to open. As the vacuum signal weakens at 5.4 kPa (1.5 in-Hg) or less, the spring force closes the valve. The EGR valve is fully open at about 15 kPa (4.5 in-Hg).
5. EGR Valve to Exhaust Manifold Tube
- Provides the flow path for exhaust gases to the EGR valve.
- Exhaust gas flowing through the EGR valve must first pass through the EGR metering orifice. With one side of the orifice exposed to exhaust back pressure and the other to the intake manifold, a pressure drop is created across the orifice whenever there is EGR flow. When the EGR valve closes, there is no longer flow across the metering orifice and pressure on both sides of the orifice is the same. The PCM constantly targets a desired pressure drop across the metering orifice to achieve the desired EGR flow.
6. Differential Pressure Feedback EGR Sensor
- Measures the actual pressure drop across the metering orifice and relays a proportional voltage signal (0 - 5 volts) to the PCM. The PCM uses this feedback signal to correct for any errors in achieving the desired EGR flow.