Nissan/Datsun 200SX/510/610/710/810/Maxima 1973-1984 Repair Guide

Exhaust Gas Recirculation (EGR)

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DESCRIPTION



Gasoline Engines


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Fig. Fig. 1 Typical EGR system flow-carbureted models



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Fig. Fig. 2 View of the EGR system used on 810 models

This system is used on all 1974-84 and later models. Exhaust gas recirculation is used to reduce combustion temperatures in the engine, thereby reducing the oxides of nitrogen emissions.

An EGR valve is mounted on the center of the intake manifold. The recycled exhaust gas is drawn into the bottom of the intake manifold riser portion through the exhaust manifold heat stove and EGR valve. A vacuum diaphragm is connected to a timed signal port at the carburetor flange.

As the throttle valve is opened, vacuum is applied to the EGR valve vacuum diaphragm. When the vacuum reaches about 2 in. Hg, the diaphragm moves against string pressure and is in a fully up position at 8 in. Hg 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.

On 1975-84 and later models, a thermal vacuum valve inserted in the engine thermostat housing controls the application of the vacuum to the EGR valve. 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.

All 1978-79 models, the 1980 810 and the 1980-81 510 (Canadian), 200SX (Canadian) have a B.P.T. valve installed between the EGR valve and the thermal vacuum valve. The B.P.T. 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 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 1980 200SX (USA) models and all 1980-81 510 (USA) models use a V.V.T. valve (venturi vacuum transducer valve) instead of the B.P.T. valve. The V.V.T. 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 flow rate as compared to the B.P.T. unit.

1981 510s built for California are equipped with two EGR valves. The second one is directly below the normal one.

Many 1975 and later Datsuns are equipped with an EGR warning system which signals via a light in the dashboard that the EGR system may need service. The EGR warning light should come on every time the starter is engaged as a test to make sure the bulb is not blown. The system uses a counter which works in conjunction with the odometer, and lights the warning signal after the vehicle has traveled a predetermined number of miles.

To reset the counter, which is mounted in the engine compartment, remove the grommet installed in the side of the counter and insert the tip of a small screwdriver into the hole. Press down on the knob inside the hole. Reinstall the grommet.

Diesel Engines

This system is designed to control the formation of NOx emissions by recirculating the exhaust gas into the intake manifold passage through the control valve.

The EGR flow rate is controlled in three stages in accordance with the engine speed and load. The first stage, High EGR, is obtained through the combination of a closed throttle valve and an open EGR valve. The second stage, Low EGR, is obtained through the opening of the throttle valve. The third stage, Zero EGR, is obtained closing the EGR valve.

The engine load signal is picked up by the potentiometer installed on the injection pump control lever. The engine speed signal is transmitted by an electromagnetic revolution sensor attached to the front cover. The throttle diaphragm and the EGR valve are both actuated by vacuum generated at the vacuum pump. Solenoids are used to convert the electrical signal from the control unit into the vacuum signal.

The EGR system is deactivated under extremely high or low coolant temperatures in order to assure good driveability.

TESTING



Gasoline Engines
1974 MODELS


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Fig. Fig. 3 Apply vacuum to the EGR valve to test for proper operation



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Fig. Fig. 4 Clean the seat of the EGR valve with a stiff brush

Check the operation of the EGR system as follows:

  1. Visually inspect the entire EGR control system. Clean the mechanism free of oil and dirt. Replace any rubber hoses found to be cracked or broken.
  2.  
  3. Make sure that the EGR solenoid valve is properly wired.
  4.  
  5. Increase the engine speed from idling to 2,000-3,500 rpm. The plate of the EGR control valve diaphragm and the valve shaft should move upward as the engine speed is increased.
  6.  
  7. Disconnect the EGR solenoid valve electrical leads and connect them directly to the vehicle's 12v electrical supply (battery). Race the engine again with the EGR solenoid valve connected to a 12v power source. The EGR control valve should remain stationary.
  8.  
  9. With the engine running at idle, push up on the EGR control valve diaphragm with your finger. When this is done, the engine idle should become rough and uneven.
  10.  

Inspect the two components of the EGR system as necessary in the following manner:

  1. Remove the EGR control valve from the intake manifold.
  2.  
  3. Apply 4.7-5.1 in. Hg of vacuum to the EGR control valve by sucking on a tube attached to the outlet on top of the valve. The valve should move to the full up position. The valve should remain open for more than 30 seconds after the application of vacuum is discontinued and the vacuum hose is blocked.
  4.  
  5. Inspect the EGR valve for any signs of warpage or damage.
  6.  
  7. Clean the EGR valve seat with a brush and compressed air to prevent clogging.
  8.  
  9. Connect the EGR solenoid valve to a 12v DC power source and notice if the valve clicks when intermittently electrified. If the valve clicks, it is considered to be working properly.
  10.  
  11. Check the EGR temperature sensing switch by removing it from the engine and placing it in a container of water together with a thermometer. Connect a self powered test light to the two electrical leads of the switch.
  12.  
  13. Heat the container of water.
  14.  
  15. The switch should conduct current when the water temperature is below 77°F (25°C) and stop conducting current when the water reaches a temperature somewhere between 88-106°F (31-41°C). Replace the switch if it functions otherwise.
  16.  

1975-84 MODELS
  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.  
  9. 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.
  10.  
  11. Place the valve in a container of water with a thermometer and heat the water. When the temperature of the water reaches 134-145°F (57-63°C), remove the valve and apply vacuum to the ports. The valve should allow vacuum to pass through it.
  12.  
  13. To test the B.P.T. valve installed on 1978 and later models, 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.
  14.  
  15. To test the check valve installed in some 1978 and later models, remove the valve and blow into the side which connects the EGR valve. Air should flow. When air is supplied to the other side, air flow resistance should be greater. If not, replace the valve.
  16.  
  17. To check the V.V.T. valve which replaces the B.P.T. valve on some 1980 and later models, 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.
  18.  

Diesel Engines


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Fig. Fig. 5 To check the EGR valve for binding or sticking, push your finger up on the diaphragm-diesel engine



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Fig. Fig. 6 The position of this lever will tell you whether the throttle valve is open or closed

  1. Visually check the entire EGR system as detailed in the previous Gasoline Engine information.
  2.  
  3. With the engine off, check the EGR control valve and throttle body for an indication of binding or sticking by moving the diaphragm/rod upward with your finger.
  4.  
  5. Start the engine and place your finger on the underside of the EGR valve. You should feel the diaphragm.
  6.  


CAUTION
Be careful that your finger doesn't get caught between the diaphragm and the body of the valve.

  1. When the temperature of the engine is at or below 86°F (30°C), make sure that the EGR valve does not operate and the throttle valve is open when the engine is revved.
  2.  
  3. If the EGR valve operates or the throttle valve is closed, check the water temperature sensor. If the sensor appears normal, replace the EGR control unit.
  4.  
  5. When the temperature of the engine is high, above 86°F (30°C), make sure that the EGR valve operates and the throttle valve is closed when the engine is idling.
  6.  
  7. Increase the engine speed gradually and make sure that the throttle valve opens and the EGR valve closes in this order.
  8.  
  9. If the EGR valve and/or the throttle valve do not operate properly in this step, check them as follows:
  10.  
    1. Run the engine at idle and disconnect the harness connector at the solenoid valve. Apply battery voltage to the connector and check that the EGR valve and the throttle valve operate normally.
    2.  
    3. If they do not, check the EGR valve and the throttle diaphragm independently. If they operate normally, check the rev sensor, the potentiometer and all electrical circuits. If they appear normal, replace the EGR control unit.
    4.  


REMOVAL & INSTALLATION



EGR Control Valve
  1. Remove the nuts which attach the EGR tube and/or the BP tube to the EGR valve (if so equipped).
  2.  
  3. Unscrew the mounting bolts and remove the heat shield plate from the EGR control valve (if so equipped).
  4.  
  5. Tag and disconnect the EGR vacuum hose(s).
  6.  
  7. Unscrew the mounting bolts and remove the EGR control valve.
  8.  
  9. Install the EGR valve assembly with mounting bolts to intake manifold location.
  10.  
  11. Connect all vacuum hoses and install the heat shield if so equipped.
  12.  
  13. Connect EGR tube or BP tube to the EGR valve if so equipped.
  14.  

Always be sure that the new valve is identical to the old one.

TESTING





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Fig. Fig. 7 Disconnect the following to remove the EGR valve where shown



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Fig. Fig. 8 Some models have two EGR valves



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Fig. Fig. 9 To remove the EGR valve, unbolt it from the exhaust manifold flange



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Fig. Fig. 10 Lift off the EGR valve from its flange-you may want to label the vacuum hose (arrow)

  1. Visually check the entire EGR system as detailed in the previous Gasoline Engine information.
  2.  
  3. With the engine off, check the EGR control valve and throttle body for an indication of binding or sticking by moving the diaphragm/rod upward with your finger.
  4.  
  5. Start the engine and place your finger on the underside of the EGR valve. You should feel the diaphragm.
  6.  


CAUTION
Be careful that your finger doesn't get caught between the diaphragm and the body of the valve.

  1. When the temperature of the engine is at or below 86°F (30°C), make sure that the EGR valve does not operate and the throttle valve is open when the engine is revved.
  2.  
  3. If the EGR valve operates or the throttle valve is closed, check the water temperature sensor. If the sensor appears normal, replace the EGR control unit.
  4.  
  5. When the temperature of the engine is high, above 86°F (30°C), make sure that the EGR valve operates and the throttle valve is closed when the engine is idling.
  6.  
  7. Increase the engine speed gradually and make sure that the throttle valve opens and the EGR valve closes in this order.
  8.  
  9. If the EGR valve and/or the throttle valve do not operate properly in this step, check them as follows:
  10.  
    1. Run the engine at idle and disconnect the harness connector at the solenoid valve. Apply battery voltage to the connector and check that the EGR valve and the throttle valve operate normally.
    2.  
    3. If they do not, check the EGR valve and the throttle diaphragm independently. If they operate normally, check the rev sensor, the potentiometer and all electrical circuits. If they appear normal, replace the EGR control unit.
    4.  


 
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