Nissan Pick-ups and Pathfinder 1989-1995

Exhaust Gas Recirculation (EGR) System

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OPERATION



See Figures 1 and 2

Exhaust gas recirculation is used to reduce combustion temperatures in the engine, thereby reducing the oxides of nitrogen (NOx) emissions. An EGR valve assembly with a gasket is mounted on the intake manifold. An EGR valve vacuum diaphragm is connected to a timed signal port at the intake manifold.

As the throttle valve is opened, vacuum is applied to the EGR valve vacuum diaphragm. When the vacuum reaches about 2.0 in. Hg (6.7 kPa), the diaphragm moves against spring pressure and is in a fully up position at 8 in. Hg (7.0 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.

Some models have a Back Pressure Transducer (BPT) valve installed between the EGR valve and the thermal vacuum valve. The BPT valve has a diaphragm raised or lowered by exhaust back pressure. The diaphragm opens or closes an air bleed, which is connected into the EGR vacuum line. High pressure results in higher levels of EGR, because the diaphragm is raised, closing off the air bleed, which allows more vacuum to reach and open the EGR valve. Thus, the amount of recirculated exhaust gas varies with exhaust pressure.

All models utilize an EGR control solenoid valve. At both low and high engine rpm, the solenoid valve turns on and causes the EGR control valve to cut the flow of gases leading to the intake manifold.



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Fig. Fig. 1: EGR system-VG30i engine (VG30E engine similar)



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Fig. Fig. 2: EGR system-Z4i engine (KA4E engine similar)

TESTING



EGR Control Valve

See Figures 3, 4 and 5

  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.
  4.  
  5. Check the valve for damage, such as warpage, cracks, and excessive wear around the valve and seat.
  6.  
  7. Clean the seat with a brush and compressed air and remove any deposits from around the valve and port (seat).
  8.  



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Fig. Fig. 3: Checking the EGR control valve



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Fig. Fig. 4: Checking the EGR control valve



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Fig. Fig. 5: Cleaning the EGR control valve

EGR Control Solenoid Valve

See Figures 6 and 7

Disconnect the solenoid valve harness connector and then apply battery voltage (12V) to terminals 1 and 2. There should be continuity between ports A and B . There should be NO continuity between ports B and C . If your readings do not agree with these, replace the solenoid valve.



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Fig. Fig. 6: Checking the EGR control solenoid valve-1989



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Fig. Fig. 7: Checking the EGR control solenoid valve-1990 and later

Thermal Vacuum Valve (TVV)

See Figure 8

To check the operation of the thermal vacuum valve, remove the valve from the engine and apply vacuum to the ports of the valve. The valve should not allow vacuum to pass.

Place the valve in a container of water with a thermometer and heat the water. When the temperature of the water reaches 134-145F (57-63C), remove the valve and apply vacuum to the ports; the valve should allow vacuum to pass through it.



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Fig. Fig. 8: Checking the TVV valve

Back Pressure Transducer (BPT) Valve

See Figure 9

To test the BPT valve, disconnect the two vacuum hoses from the valve. Plug one of the ports. While applying pressure to the bottom of the valve, apply vacuum to the unplugged port and check for leakage. If any exists, replace the valve.



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Fig. Fig. 9: Checking the BPT valve

ADJUSTMENT



No adjustments are either necessary or possible to this system.

REMOVAL & INSTALLATION



See Figures 10, 11, 12, 13 and 14

  1. Remove the nut which attaches the EGR tube and/or the back pressure tube to the EGR valve (if so equipped).
  2.  
  3. Unscrew the mounting bolts and remove the heat shield between the EGR control valve (if equipped with a heat shield), and the intake manifold.
  4.  
  5. Tag and disconnect the EGR vacuum hose(s).
  6.  
  7. Unscrew the mounting bolts and remove the EGR control valve.
  8.  

To install:
  1. Install the EGR valve assembly (using a new gasket) with mounting bolts to the intake manifold location.
  2.  
  3. Connect all vacuum hoses, and install the heat shield between the EGR control valve and the intake manifold, if equipped with a heat shield.
  4.  
  5. Connect the EGR tube and/or the back pressure tube to the EGR valve, if so equipped.
  6.  

If replacing the EGR valve, always be sure that the new valve is identical to the old one.



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Fig. Fig. 10: Removing the EGR line from the valve assembly



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Fig. Fig. 11: After removing the EGR line reposition it away for added working room



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Fig. Fig. 12: Removing the vacuum line from the valve assembly



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Fig. Fig. 13: Removing the EGR valve assembly mounting bolt



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Fig. Fig. 14: Be sure to replace the mounting gasket upon installation

 
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