Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Exhaust Gas Recirculation (EGR) System

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OPERATION



See Figures 1, 2, 3, 4 and 5

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Fig. Fig. 1: EGR system-carbureted vehicle without a computer controlled engine



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Fig. Fig. 2: EGR system-fuel injected vehicle with a computer controlled engine



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Fig. Fig. 3: Cutaway view of an EGR thermo-vacuum valve assembly



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Fig. Fig. 4: Cutaway view of an EGR solenoid valve-carbureted and SPFI engines



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Fig. Fig. 5: Cutaway view of an EGR solenoid valve-multi-port fuel injected engine

The function of the Exhaust Gas Recirculation (EGR) system is the reduction of NOx (oxides of nitrogen) by reducing the combustion temperature through recirculating a part of the exhaust gas into the cylinders.

The EGR valve opens in response engine vacuum. A thermo-valve, or on computer controlled engines a solenoid valve, is used to control the amount of vacuum reaching the EGR valve. When engine performance would suffer due to the recirculating gasses, normally during start-up, the valves remained closed to not allow vacuum to reach the EGR valve. When predetermined conditions are met, the valves open to allow the EGR valve to function according engine vacuum.

TESTING



The EGR system on the Legacy, Impreza and SVX is diagnosed and tested via the on-board diagnostics.

EGR Valve and Flow Passages

See Figure 6

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Fig. Fig. 6: Checking the EGR valve with a vacuum pump. This can be done with the valve on or off the engine

  1. Start the engine and allow it to reach normal operating temperature.
  2.  
  3. Looking through the opening in the EGR valve body, check if the valve shaft moves when the engine is revved to 3000-3500 rpm under a no load condition. If the shaft moves, proceed to Step 4.
  4.  

During the test in Step 2, the EGR solenoid valve should be removed from SPFI engines.

  1. If the shaft does not move, check the EGR valve with a hand vacuum pump. Apply 8 in. Hg (27 kPa) of vacuum and see if the shaft moves. If not, remove the valve and clean or replace as needed. If the valve functions properly, check for leaks in the EGR vacuum lines.
  2.  
  3. With the engine idling, connect a hand vacuum pump to the EGR valve. Apply 8 in. Hg (27 kPa) of vacuum to the valve. The engine should stall or idle roughly. If not, clean the obstruction from the exhaust gas passages in the cylinder head.
  4.  

EGR VALVE CLEANING

See Figure 7

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Fig. Fig. 7: Using a plastic hammer to clean an EGR valve

Do not wash the EGR valve in solvent, as permanent damage could result.

  1. Hold the valve assembly in hand and lightly tap with a plastic hammer to remove the exhaust deposits from the valve seat.
  2.  
  3. With a wire brush, remove the deposits from the mounting surfaces of the valve.
  4.  
  5. Depress the valve and look at the seat area. If valve and seat are not clean, repeat the cleaning procedure.
  6.  
  7. Look for deposits in the valve outlet and remove with an appropriate tool.
  8.  
  9. Blow any remaining deposits from the valve with compressed air.
  10.  
  11. Check the EGR valve for proper operation using a hand vacuum pump.
  12.  

EXHAUST GAS PASSAGE CLEANING
  1. Inspect the EGR gas inlet to intake manifold for carbon or oil deposits. Remove any deposits present with a hooked awl, taking care to minimize the amount of material falling into the intake manifold.
  2.  
  3. Remove all deposits using a vacuum.
  4.  
  5. Remove the EGR pipe and lightly tap with a plastic hammer to loosen deposits. Blow clean using compressed air.
  6.  

Thermo-Vacuum Valve

This valve is used only on non-computer controlled engines.

  1. Drain the cooling system and remove the thermo-vacuum valve.
  2.  
  3. With the valve at 86°F (30°C) or less, air should pass through the first and second port when the third port is plugged. Air should pass through the second and third port when the first port is plugged.
  4.  
  5. Heat the valve to 104°F (40°C) and repeat the tests in Step 2. Air should not pass any of the ports.
  6.  
  7. If the valve does not function properly, remove and replace it.
  8.  

Vacuum Solenoid Valve
  1. Disconnect the electrical harness.
  2.  
  3. Check the resistance between the positive and negative terminals of the valve. Resistance should be 33-40 ohms.
  4.  
  5. Check the resistance between the positive or negative terminals and the body. Resistance should be 1M ohm or more.
  6.  
  7. Check the vacuum passage for opening and closing operation while applying electric current on both the positive and negative terminals. With no electricity applied, the passage between the EGR and intake manifold ports should be open. When the electricity is applied, the passage between the EGR and intake manifold ports should be closed.
  8.  
  9. If the valve does not function properly, it should be replaced.
  10.  

REMOVAL & INSTALLATION



EGR Valve

See Figures 8 and 9

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Fig. Fig. 8: EGR valve attached to the side of the intake manifold-Loyale



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Fig. Fig. 9: Loosen and remove the EGR valve retainer nuts-Legacy

  1. Detach the vacuum hose from the EGR valve.
  2.  
  3. Remove the two nuts which secure the EGR valve to the intake manifold assembly.
  4.  
  5. Remove the valve and gasket from the manifold.
  6.  
  7. Clean all gasket material from both mating surfaces.
  8.  
  9. Check the vacuum hose for deterioration and replace as necessary.
  10.  

To install:
  1. Inspect the exhaust gas passages in the intake manifold and clean as necessary. Clean the EGR valve assembly as necessary.
  2.  
  3. Using a new gasket, install the EGR valve.
  4.  
  5. Tighten the EGR valve securing nuts to 17-19 ft. lbs. (22-25 Nm).
  6.  
  7. Install the hose on the EGR valve.
  8.  

Thermo-Vacuum Valve
  1. Drain the cooling system below the level of the thermo-vacuum valve.
  2.  
  3. Tag and disconnect the vacuum hoses from the valve assembly.
  4.  
  5. Remove the thermo-valve using an appropriately sized wrench.
  6.  
  7. Inspect the vacuum hoses for signs of deterioration and replace as necessary.
  8.  

To install:
  1. Install the thermo-vacuum valve after coating the threads with sealant. Tighten the valve securely.
  2.  
  3. Connect the vacuum hoses.
  4.  
  5. Refill the cooling system.
  6.  

Vacuum Solenoid Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the vacuum solenoid wiring harness.
  4.  
  5. Tag and disconnect the vacuum hoses from the valve assembly.
  6.  
  7. Remove the solenoid valve attaching screws, then remove the solenoid valve.
  8.  

To install:
  1. Position the valve assembly, securing in place with the retainer screws.
  2.  
  3. Inspect the vacuum hoses for signs of deterioration and replace as necessary.
  4.  
  5. Connect the vacuum hoses to the valve.
  6.  
  7. Connect the vacuum solenoid wiring harness.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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