Differential Pressure Feedback EGR System: Notes
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Differential Pressure Feedback (DPFE) EGR system consists of a DPFE EGR sensor, EGR vacuum regulator solenoid, EGR valve, orifice tube assembly and Powertrain Control Module (PCM). The following list of components and their specific operation corresponds to numbers in illustration. See Fig 1.
- DPFE EGR system receives signals from Engine Coolant Temperature (ECT) sensor, Intake Air Temperature (IAT) sensor, Throttle Position (TP) sensor, Mass Airflow (MAF) sensor and Crankshaft Position (CKP) sensor to provide information on engine operating conditions to PCM. Engine must be warm, stable and running at a moderate load and engine speed (RPM) before EGR system is activated. PCM deactivates EGR during idle, extended Wide Open Throttle (WOT), or whenever a failure is detected in an EGR component or EGR required input.
- PCM calculates desired amount of EGR flow for a given engine condition. It then determines desired pressure drop across metering orifice required to achieve that flow and outputs corresponding signal to EGR vacuum regulator solenoid.
- EGR vacuum regulator solenoid receives a variable duty cycle signal between 0-100 percent. The higher the duty cycle, the more vacuum the solenoid diverts to EGR valve. For additional EGR vacuum regulator solenoid information, see EGR VACUUM REGULATOR SOLENOID .
- The increase in vacuum acting on EGR valve diaphragm overcomes valve spring and begins to lift EGR valve pintle off its seat, causing exhaust gas to flow into intake manifold.
- Exhaust gas flowing through EGR valve must first pass through EGR metering orifice (orifice tube). With one side of orifice exposed to exhaust backpressure and other to intake manifold, a pressure drop is created across orifice whenever there is EGR flow. When EGR valve closes, there is no longer flow across metering orifice and pressure on both sides of orifice is the same. PCM constantly targets a desired pressure drop across metering orifice to achieve desired EGR flow. For additional orifice tube assembly information, see ORIFICE TUBE ASSEMBLY .
- DPFE EGR sensor measures actual pressure drop across metering orifice and relays a proportional voltage signal between 0-5 volts to PCM. See Fig 2. PCM uses this feedback signal to correct for any errors in achieving desired EGR flow. For additional DPFE EGR sensor information, see REMOTE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR or TUBE MOUNTED DIFFERENTIAL PRESSURE FEEDBACK EGR SENSOR .