Exhaust Gas Recirculation: Description and Operation
ELECTRONIC EXHAUST GAS RECIRCULATION (EEGR)Typical Electronic EGR System:
The Electronic Exhaust Gas Recirculation (EEGR) System is controlled by the EEC Module, based on return signals from various engine components. The EEGR System utilizes a valve position sensor, and a solenoid-type vacuum regulator device. Circuit power is supplied through the EEC Module power relay, and circuit ground is provided internally by the EEC Module.
The EGR Valve Position (EVP) Sensor informs the EEC Module of the EGR Valves position through a voltage return signal. This signal is directly proportional to the amount of exhaust gas being recirculated. The EGR Vacuum Regulator (EVR) controls the vacuum applied to the EGR valve diaphragm.
NOTE: Other Vacuum Related Components may be incorporated into the EEGR System, depending on vehicle model and Calibration.
EGR VALVE
EGR Valve And Sensor Assembly:
The Electronic EGR Valve, generally located at one side of the engine toward the top, is equipped with a position sensor. The EGR Valve Position (EVP) Sensor sends a voltage signal to the EEC Module in relation to the opening of the EGR Valve.
The Valve is actuated and controlled by vacuum, supplied from the EGR Vacuum Regulator (EVR). When vacuum from the EVR overcomes diaphragm spring pressure, the diaphragm lifts the pintle valve from its seat, allowing exhaust gases to recirculate. The EEC Module regulates EGR flow based on engine load, temperature, and current EGR Valve opening and/or flow.
The EVP Sensor and EGR Valve are non-serviceable and must be replaced individually.
EGR VALVE POSITION (EVP) SENSOR
EGR valve position sensor:
The EGR Valve Position (EVP) Sensor is a linear potentiometer mounted on top of the EGR Valve. The EVP Sensor returns a voltage signal to the EEC Module indicating whether the valve is opened, closed, or somewhere in between. The voltage signal is in direct relation with the valves movement.
An example of this relationship is as follows:
EGR OPENING VOLTAGES - BLACK SENSOR GRAY SENSOR
0% .90 volts .35 volts
10% 1.25 volts .75 volts
20% 1.65 volts 1.10 volts
30% 1.95 volts 1.45 volts
40% 2.30 volts 1.80 volts
50% 2.65 volts 2.15 volts
60% 3.00 volts 2.50 volts
70% 3.35 volts 2.85 volts
80% 3.70 volts 3.20 volts
90% 4.05 volts 3.55 volts
100% 4.40 volts 3.90 volts
NOTE: EGR closed position is very important. Timing is retarded if EGR flow is low.
EGR VACUUM REGULATOR (EVR)
EGR Vacuum Regulator (EVR) Solenoid:
The EGR Vacuum Regulator (EVR) is a single unit electromagnetic device with two vacuum ports. The EVR allows the EEC Module to modulate the EGR Valves opening to any degree, by providing the circuits ground, internally.
The upper port is connected to the vacuum chamber of the EGR Valve. The lower port is connected to manifold vacuum or ported vacuum, depending upon system design. Atmospheric pressure is present on one side of the metal disc at all times. This is provided by the vented cover and a hollow electromagnetic core. The disc at the bottom of the core is held in place by a weak spring.
While the EVR is not energized (engine running), a low pressure area develops below the disc from engine vacuum. With this pressure differential, the spring is not strong enough to keep atmospheric pressure from entering the EVR vacuum passages. Vacuum is not applied to the EGR Valve diaphragm, thus the EGR Valve remains closed.
When the EEC Module grounds the EVR circuit, a magnetic field is produced from the energized coil. This magnetic field pulls the metal disc against the cores bottom, sealing off the vacuum passages. Engine vacuum is now applied to the EGR Valve and the valve opens. The EEC Module cycles the EVR ON and OFF rapidly in order to control EGR valve opening and therefore exhaust recirculation flow.