Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

Exhaust Gas Recirculation System

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OPERATION



See Figures 1 and 2



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Fig. Fig. 1: EGR system diagram-early system without electronic feedback



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Fig. Fig. 2: Common EGR system-1991-96 vehicles

All Sentra/Pulsar engines use an Exhaust Gas Recirculation (EGR) system. The EGR system is used to reduce combustion temperatures in the engine, thereby reducing the oxides of nitrogen emissions and controlling detonation (ping).

The methods of controlling this function, vary greatly from engine-to-engine. For specific system usage, refer to the engine vacuum schematics provide in this section.

Exhaust Gas Recirculation (EGR) Valve

See Figure 3



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Fig. Fig. 3: Cutaway view of a typical EGR valve

On all engines, the EGR valve is mounted on the intake manifold. The recycled exhaust gas is drawn into the intake manifold, through the exhaust manifold and controlled by the EGR valve. As the throttle valve is opened, vacuum is applied to the EGR valve vacuum diaphragm. The diaphragm moves a tapered valve, that allows exhaust gas to pass into the intake manifold. When the vacuum reaches about 2 in. Hg (7 kPa), the diaphragm moves against spring pressure and is in a fully up (open) position at about 8 in. Hg (27 kPa) of vacuum. As the diaphragm moves up, it opens the exhaust gas metering valve which allows exhaust gas to be pulled into the engine intake manifold. The system does not operate when the engine is idling because the exhaust gas recirculation would cause a rough idle.

EGR Back Pressure Transducer (BPT) Valve

See Figure 4



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Fig. Fig. 4: Cutaway view of BPT valve

Some engines have a Back Pressure Transducer (BPT) valve installed between the EGR valve. The BPT valve has a diaphragm which is raised or lowered by exhaust back pressure. The diaphragm opens or closes an air bleed, which is connected into the EGR vacuum line. High exhaust pressure raises the diaphragm, closing off the air bleed. When the air bleed is closed, more vacuum reaches the EGR valve, thus opening the valve further.

Exhaust Gas Recirculation (EGR) Control Solenoid

On most later carbureted engines and all fuel injected engines, the EGR control solenoid replaces the thermal vacuum switch. The control solenoid operation is controlled by the ECM, which uses inputs received from the CPS, MAF, ECT and ignition switch to determine if the EGR system should be enabled. When the ECM energizes the solenoid, the plunger in the solenoid cuts the vacuum supply to the EGR valve and EVAP purge valve off. When EGR function is desired, the ECM de-energizes the solenoid.

Exhaust Gas Recirculation (EGR) Temperature Sensor

The sensor sends a voltage signal to the ECM proportional to the EGR passage temperature. As the exhaust flow increases, the EGR passage temperature increases, causing the EGR temperature sensor resistance to decreases. The decrease in resistance causes the sensor reference line voltage to drop. The ECM can calculate the EGR system efficiency, by monitoring voltage changes in the temperature sensor circuit.

Exhaust Gas Recirculation (EGR) Thermal Vacuum Valve

Many early systems use a thermal vacuum valve inserted in the engine thermostat housing which prevents EGR operation when the engine is cold. The valve controls the application of the vacuum to the EGR valve, according to engine temperature. When the engine coolant reaches a predetermined temperature, the thermal vacuum valve opens and allows vacuum to be routed to the EGR valve. Below the predetermined temperature, the thermal vacuum valve closes and blocks vacuum to the EGR valve.

Exhaust Gas Recirculation (EGR) Venturi Vacuum Transducer (VVT)

1982 1.5L engines use a Venturi Vacuum Transducer (VVT) valve. The VVT valve monitors exhaust pressure and carburetor vacuum in order to activate the diaphragm which controls the throttle vacuum applied to the EGR control valve. This system expands the operating range of the EGR unit, as well as increasing the EGR flow rate.

TESTING



Exhaust Gas Recirculation (EGR) Valve

See Figure 5



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Fig. Fig. 5: Some EGR valves may be tested using a vacuum pump by watching for diaphragm movement

  1. Remove the EGR valve and apply enough vacuum to the diaphragm to open the valve.
  2.  
  3. The valve should remain open for over 30 seconds after the vacuum is removed.

    If the valve holds vacuum, proceed to the next step.
     
    If the valve does not hold vacuum, replace the valve assembly.
     

  4.  
  5. Check the valve for damage, such as warpage, cracks and excessive wear around the valve and seat. If necessary, clean the seat with a brush and compressed air, then remove any deposits from around the valve and port (seat).
  6.  

Exhaust Gas Recirculation (EGR) Back Pressure Transducer Valve

See Figure 6



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Fig. Fig. 6: EGR-BPT valve testing

  1. Disconnect the two vacuum hoses from the valve. Plug one of the ports.
  2.  
  3. While applying pressure to the bottom of the valve, apply vacuum to the unplugged port and check for leakage. If any leakage exists, replace the valve.
  4.  

Exhaust Gas Recirculation (EGR) Control Solenoid

See Figures 7, 8 and 9



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Fig. Fig. 7: EGR/EVAP control solenoid vacuum port identification-1987-90 vehicles



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Fig. Fig.8: EGR/EVAP control solenoid vacuum port and electrical terminal identification-1991-94 vehicles



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Fig. Fig. 9: EGR/EVAP control solenoid vacuum port and electrical terminal identification-1995-96 vehicles

  1. Mark and tag all vacuum lines attached to the control valve. Once marked, remove the hoses from the control assembly.
  2.  
  3. Apply 12V to terminal 2 , and ground to terminal 1 .
  4.  
  5. With the solenoid energized, check for air passage between vacuum fittings as follows:

    Ports A and B 1987-96 engines-Passage open-air should pass freely
     
    Ports B and C 1987-94 engines-Passage blocked-no air should not pass
     
    Ports A and C 1995-96 engines-Passage blocked-no air should not pass
     

  6.  
  7. Disconnect the 12V power supply. With the solenoid de-energized check for air passages between the vacuum fittings as follows:

    Ports A and B 1987-96 engines-Passage blocked-no air should not pass
     
    Ports B and C 1987-94 engines-Passage open-air should pass freely
     
    Ports A and C 1995-96 engines-Passage open-air should pass freely
     

  8.  
  9. If the solenoid did not perform as specified, replace the EGR/EVAP solenoid/valve assembly.
  10.  

Exhaust Gas Recirculation (EGR) Temperature Sensor

See Figure 10



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Fig. Fig. 10: EGR temperature sensor testing

  1. Disconnect the EGR temperature sensor harness connector
  2.  
  3. Remove the EGR temperature sensor from the engine.
  4.  
  5. Place the sensor in water.
  6.  
  7. Heat the water to boiling and measure the resistance across the EGR temperature sensor connector terminals
  8.  
  9. Resistance should be 76-94 kilo-ohms with the EGR temperature sensor at 212°F (100°C).
  10.  

Exhaust Gas Recirculation (EGR) Thermal Vacuum Valve

See Figure 11



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Fig. Fig. 11: EGR thermal vacuum valve testing

  1. Remove the EGR thermal vacuum valve from the engine.
  2.  
  3. Connect a vacuum pump to the air cleaner port (upper port).
  4.  
  5. Plug either of the remaining ports.
  6.  
  7. Apply vacuum to the air cleaner port; it should allow vacuum to pass. Repeat the test for other port. If either port was closed, replace the vacuum valve.
  8.  


WARNING
Do not allow water to enter the vacuum passages when testing, or the valve may be damaged.

  1. Place the valve in a container of water with a thermometer and heat the water. When the temperature of the water reaches approximately 122°F (50°C). Repeat the above test procedure. Vacuum should not pass through either passage, if it does replace the valve.
  2.  

Exhaust Gas Recirculation (EGR) Venturi Vacuum Transducer (VVT)

To check the VVT valve, disconnect the top and bottom center hoses and apply a vacuum to the top hose. Check for leaks. If a leak is present, replace the valve.

REMOVAL & INSTALLATION



Exhaust Gas Recirculation (EGR) Valve

See Figures 12, 13 and 14



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Fig. Fig. 12: With the air cleaner inlet hose removed, disconnect the vacuum supply hose from the EGR valve



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Fig. Fig. 13: Disconnect the exhaust inlet pipe from the manifold, then detach the pipe from the EGR valve



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Fig. Fig. 14: Remove the two nuts from the mounting studs and remove the EGR valve from the intake manifold

  1. Remove the air inlet hose from the throttle housing, if required.
  2.  
  3. Mark and tag any vacuum lines attached to the EGR valve. Once marked, unplug the vacuum hoses.
  4.  
  5. If equipped, disconnect the exhaust feed tube from the valve assembly.
  6.  
  7. Loosen and remove the 2 bolts securing the EGR valve to the engine. Remove the EGR valve from the engine compartment.
  8.  
  9. Remove any gasket material from the mating surfaces.
  10.  

To install:
  1. Using a new gasket, position the valve to the intake and secure with the retaining bolts. Tighten the bolts completely with a suitable wrench.
  2.  
  3. Connect the exhaust feed tube to the valve, if removed.
  4.  
  5. Attach the vacuum hoses to the EGR valve, in their correct order.
  6.  
  7. Connect the air inlet hose, if removed.
  8.  

Exhaust Gas Recirculation (EGR) Back Pressure Transducer Valve

  1. Mark and tag all vacuum hose attached to the BPT valve. Once tagged, remove the vacuum hoses from the assembly.
  2.  
  3. Slide the valve from its mounting bracket.
  4.  

To install:
  1. Slide valve back into the mounting bracket.
  2.  
  3. Reconnect vacuum hoses to the appropriated port.
  4.  

Exhaust Gas Recirculation (EGR) Control Solenoid
  1. Mark and tag all vacuum hose attached to the control solenoid. Once tagged, remove the vacuum hoses from the assembly.
  2.  
  3. Unplug the sensor harness connector from the control solenoid.
  4.  
  5. Remove the control solenoid from the engine compartment by either unfastening the retaining bolts which secure the control solenoid and bracket, or remove the solenoid from the bracket by loosening the tabs at the rear of the unit.
  6.  

To install:
  1. Depending on how the control solenoid was removed, install the valve by either inserting the bracket into the tabs at the rear of the unit, or secure the control solenoid and bracket using the retaining bolts.
  2.  
  3. Plug the sensor harness connector into the control solenoid.
  4.  
  5. Connect the vacuum hoses to their original locations.
  6.  

Exhaust Gas Recirculation (EGR) Temperature Sensor
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the wiring harness.
  4.  
  5. Unscrew the EGR sensor.
  6.  

To install:
  1. Install the EGR sensor and torque to 11 ft. lbs. (15 Nm).
  2.  
  3. Connect the wire harness.
  4.  
  5. Connect the negative battery cable.
  6.  

Exhaust Gas Recirculation (EGR) Thermal Vacuum Valve
  1. Drain the engine coolant.
  2.  
  3. Tag and disconnect the vacuum hoses from the valve.
  4.  
  5. Using the correct size wrench, remove the sensor.
  6.  

To install:
  1. Coat the threads of the new valve with an approved anti-seize compound.
  2.  
  3. Install the new sensor using the correct size wrench.
  4.  
  5. Reconnect the vacuum hoses to the appropriate fitting.
  6.  
  7. Refill the engine coolant.
  8.  
  9. Run the engine until the cooling fans operate and check for leaks.
  10.  

 
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