Volvo 240/740/760/780/940/960 1990-1998

Exhaust Gas Recirculation System

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OPERATION



System

See Figure 1



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Fig. Fig. 1: Diagram of the EGR system

The Exhaust Gas Recirculation (EGR) system is designed to reintroduce exhaust gas into the combustion chambers, thereby lowering combustion temperatures and reducing the formation of oxides of nitrogen (NO x ).

The amount of exhaust gas that is reintroduced into the combustion cycle is determined by several factors, such as: engine speed, engine vacuum, exhaust system backpressure, coolant temperature, throttle position. All EGR valves are vacuum operated. The EGR vacuum diagram for your particular vehicle is displayed on the Vehicle Emission Control Information (VECI) label.

EGR Valve

See Figure 2



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Fig. Fig. 2: A typical EGR valve

The EGR valve controls flow of exhaust gases from the exhaust manifold to the intake manifold. The valve is operated by control pressure from the EGR vacuum booster. The EGR valve is located under the intake manifold.

EGR Vacuum Controller

See Figure 3



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Fig. Fig. 3: An EGR vacuum controller

The vacuum controller controls pressure in the vacuum line to the EGR valve by means of the admission valve (lower section). The pressure in the intake manifold is supplied to the reducing valve (upper section). The valve uses an electrical signal to maintain optimum control of the EGR valve. The unit is also designed to allow for ambient air pressure. The vacuum controller valve is located on the left-hand suspension strut tower or on the relay shelf above the electric cooling fan.

EGR Temperature Sensor

See Figure 4

The EGR temperature sensor measures the temperature of exhaust gases returned to the intake manifold. This sensor has a positive temperature coefficient, which means that the resistance through the sensor will rise with the temperature. The sensor is designed to measure temperatures up to 930°F (500°C). Detection of temperature variations enables the control unit to determine whether or not the EGR system is working. The sensor is located in the EGR upper pipe, between the intake manifold and EGR valve.



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Fig. Fig. 4: An EGR temperature sensor

COMPONENT TESTING



EGR Temperature Sensor

See Figure 5

  1. Unplug the temperature sensor connector.
  2.  
  3. Measure the resistance between the terminals of the sensor. The resistance should be 0.1-4000 ohms.
  4.  

Use the temperature-to-resistance chart in this section for reference. If the value is out of range, replace the sensor.

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Fig. Fig. 5: EGR temperature-to-resistance conversion chart

EGR Gas Flow Test
  1. Connect a tachometer to the engine.
  2.  
  3. Remove the vacuum hose or rubber elbow from the EGR valve and connect a hand vacuum pump to the EGR valve vacuum nipple.
  4.  
  5. Start the engine and slowly apply vacuum to the EGR valve diaphragm.
  6.  
  7. The engine speed should drop as vacuum reaches 3-5 in. Hg and continue to drop as more vacuum is applied. The engine may even stall. This means EGR gas is flowing through the system.
  8.  
  9. If the engine speed doesn't drop, check for a failed EGR valve or plugged EGR passage. Remove the EGR valve and inspect/repair as necessary.
  10.  

EGR Valve Leakage Test

See Figure 6



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Fig. Fig. 6: Remove the hose from the EGR valve to test the valve

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the hose from the fitting from the top of the EGR valve.
  4.  
  5. Connect a hand-held vacuum pump to the fitting and apply 15 inches of vacuum to the valve. Observe the gauge reading on the pump; if vacuum falls off, the diaphragm in the EGR valve has ruptured, and the EGR valve must be replaced. If vacuum remains, proceed to next step.
  6.  
  7. Remove the hose from the bottom of the EGR valve. Using compressed air (if available) and an air nozzle with rubber tip, apply 50 psi of regulated air pressure to the fitting.
  8.  
  9. Using your hand, open the throttle all the way, and listen inside the throttle body, if air is escaping, the poppet valve in the base of the EGR valve is leaking. Replace the EGR valve.
  10.  

EGR Vacuum Controller

See Figures 7, 8 and 9

  1. Remove the inlet hose of the EGR vacuum controller.
  2.  
  3. Connect a hand-held vacuum pump to the fitting and apply 10 inches of vacuum. If the vacuum falls off, the controllers diaphragm is leaking. Replace the EGR vacuum controller and retest. If OK, connect hose and proceed to the next step.
  4.  
  5. Remove the hose at the EGR vacuum controller inlet (if reinstalled after last test).
  6.  
  7. Connect a vacuum gauge to this hose.
  8.  
  9. Start the engine and bring it to operating temperature.
  10.  
  11. Hold the engine speed at approximately 1500 RPM. Check for steady manifold vacuum at this hose.
  12.  

To figure out what the vacuum should be, remove a vacuum hose directly from the intake manifold and measure the vacuum at 1500 RPM.

  1. If manifold vacuum is not present, check for vacuum leaks in the line or an obstruction. Repair as necessary and retest. If manifold vacuum was OK, shut off engine, connect hose, and proceed to the next step.
  2.  
  3. Disconnect the hose at the vacuum controller outlet fitting.
  4.  
  5. Connect a vacuum gauge to this fitting.
  6.  
  7. Disconnect the electrical connector on the controller. This will simulate an open circuit at the controller.
  8.  
  9. Start the engine and bring it to operating temperature.
  10.  
  11. Hold the engine speed at approximately 2000 RPM while checking for vacuum flow through the vacuum controller.
  12.  
  13. The gauge reading will be low, at idle speed the gauge reading should be erratic. This is normal.
  14.  
  15. To allow full manifold vacuum to flow through the vacuum controller, exhaust backpressure must be present. It must be high enough to hold the bleed valve in the transducer portion of the controller closed. Have a helper momentarily (a few seconds) block the exhaust with a rag or other suitable device.
  16.  


CAUTION
Make sure to have the helper wear heavy gloves to reduce the risk of burns from the exhaust gas or exhaust pipes.

  1. As temporary backpressure is built, full manifold vacuum should be observed.
  2.  
  3. If full vacuum was present at the inlet fitting, but is not present at the outlet fitting, replace the valve control.
  4.  



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Fig. Fig. 7: Connect a hand-held vacuum pump to the inlet of the controller to check the controller valve diaphragm



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Fig. Fig. 8: Remove the outlet hose of the controller and ...



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Fig. Fig. 9: ... connect a vacuum gauge to the port to check operation of the controller valve

REMOVAL & INSTALLATION



EGR Valve

See Figures 10, 11, 12, 13 and 14

  1. Disconnect the negative battery cable.
  2.  
  3. Remove any components necessary to access the valve.
  4.  
  5. Unplug the EGR temperature sensor (if equipped).
  6.  
  7. Remove the EGR tube from the valve.
  8.  
  9. Remove the EGR valve mounting bolts.
  10.  
  11. Remove the EGR valve from the vehicle.
  12.  

To install:
  1. Clean the valve mounting surface.
  2.  
  3. Install a new gasket on the valve mounting surface.
  4.  
  5. Install the valve into place.
  6.  
  7. Tighten the valve mounting bolts.
  8.  
  9. Insert the EGR tube and tighten the fitting.
  10.  
  11. If equipped, plug in the EGR temperature sensor connector.
  12.  
  13. Install any components removed to access the valve.
  14.  
  15. Connect the negative battery cable.
  16.  



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Fig. Fig. 10: EGR valve location on the 2.3L 4-cylinder engines



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Fig. Fig. 11: Location of the EGR valve-850 models



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Fig. Fig. 12: Remove the two valve mounting bolts and ...



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Fig. Fig. 13: ... lift the valve from the mounting surface



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Fig. Fig. 14: Always replace the EGR gasket with a new one when replacing the valve

EGR Controller Valve

  1. Disconnect the negative battery cable.
  2.  
  3. Label and remove the vacuum hoses and electrical connectors from the valve.
  4.  
  5. Remove the fasteners, then remove the valve.
  6.  

To install:
  1. Place the new valve into position and secure it with the mounting fasteners.
  2.  
  3. Attach the vacuum lines and wiring connectors to the valve.
  4.  
  5. Connect the negative battery cable.
  6.  

EGR Temperature Sensor
  1. Disconnect the negative battery cable.
  2.  
  3. Remove any necessary components to access the EGR valve and sensor.
  4.  
  5. Unplug the temperature sensor connector.
  6.  
  7. Using a proper size socket, remove the EGR temperature sensor from the valve.
  8.  

To install:
  1. Install the temperature sensor into the valve and tighten the sensor.
  2.  
  3. Plug the sensor connector in.
  4.  
  5. Install any components removed to access the valve.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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