Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Exhaust Gas Recirculation (EGR) System

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OPERATION



See Figures 1, 2 and 3

To reduce NOx (oxides of nitrogen) emissions, metered amounts of exhaust gases are added to the air/fuel mixture. The recirculated exhaust gas lowers the peak flame temperature during combustion to cut the output of oxides of nitrogen. On some early models, the exhaust gas from the manifold passes through a filter where it is cleaned. The EGR valve controls the amount of this exhaust gas which is allowed into the intake manifold. There is no EGR flow at idle, partial at slight throttle and full EGR flow at mid-throttle.

The 1974-75 models have an EGR filter and a 2-stage EGR valve. The first stage is controlled by the temperature valve. The second stage is controlled by the microswitch on the carburetor throttle valve.



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Fig. Fig. 1: EGR system components on 1974-75 models

The EGR filter was discontinued on 1976 and later models but the 2-stage EGR valve was retained. On Federal vehicles, only the first stage is connected; California vehicles use both stages. The first stage is controlled by engine vacuum and coolant temperature. The second stage is controlled by temperature, engine vacuum and a microswitch on the carburetor throttle valve.



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Fig. Fig. 2: EGR system components on 1976 models

The EGR valve on other models is controlled by a temperature valve and a vacuum amplifier.



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Fig. Fig. 3: Schematic of the a common EGR system and components used on models after 1976

TESTING



EGR Valve
1974-76 MODELS

See Figure 4

To test the first stage:

  1. Disconnect the vacuum line from the end of the EGR valve.
  2.  
  3. Disconnect the vacuum hose from the distributor vacuum unit and extend hose.
  4.  
  5. Start the engine and allow it to idle.
  6.  
  7. Connect the line from the anti-backfire valve to the EGR valve. The engine should stumble or stall.
  8.  
  9. If the idle stays even, the EGR line is clogged or the EGR valve is defective. If equipped, the EGR filter may be clogged.
  10.  

To test the second stage, manually operate the microswitch (on the carburetor) with the engine at idle. If the engine speed drops or the engine stalls, the system is operating correctly. If not, check the microswitch, the EGR filter and the EGR return lines for blockage.



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Fig. Fig. 4: Manually operate the microswitch (arrow) to check the EGR valve

1977 AND LATER MODELS

Be sure the vacuum lines are not leaking. Replace any that are leaking or cracked.

  1. Warm the engine to normal operating temperature.
  2.  
  3. Run the engine at idle.
  4.  
  5. Disconnect the vacuum hose from the EGR valve.
  6.  
  7. Apply vacuum to the EGR valve using a hand vacuum pump
  8.  
  9. If the engine speed does not change, the EGR valve is clogged or damaged.
  10.  

EGR Temperature Valve
1974-76 MODELS

See Figure 5

  1. Remove the temperature valve.
  2.  
  3. Apply vacuum to the angled connection. With the valve temperature below approximately 120°F (49°C), it should hold a vacuum.
  4.  



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Fig. Fig. 5: Angled connection on the EGR temperature valve

  1. Heat the temperature valve in a hot water bath to over 120°F (49°C). When vacuum is applied to the angled connection, it should not hold a vacuum.
  2.  

1977 AND LATER MODELS

See Figure 6

Warm the engine to normal operating temperature. With the engine at idle, attach a vacuum gauge between the EGR temperature valve and the EGR valve. The temperature valve should be replaced if the gauge shows less than 2 in. Hg. (14 kPa).



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Fig. Fig. 6: EGR temperature valve location on fuel injected engines

EGR Deceleration Valve

See Figure 7

The deceleration valve was first used on some models in 1976. No automatic transaxle Volkswagens have deceleration valves.

  1. Remove the hose leading to the air intake duct from the deceleration valve. Plug the hose.
  2.  



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Fig. Fig. 7: EGR deceleration valve location

  1. Run the engine for a few seconds at 3,000 rpm.
  2.  
  3. Snap the throttle valve closed.
  4.  
  5. With your finger, check for suction at the hose connection.
  6.  
  7. Unplug the hose from the vacuum fitting.
  8.  
  9. Run the engine at about 3,000 rpm. No suction should be felt.
  10.  

EGR Vacuum Amplifier
  1. Run the engine at idle.
  2.  
  3. Connect a vacuum gauge between the vacuum amplifier and the throttle valve port.
  4.  
  5. The gauge should read between 0.2-0.3 in. Hg. (1.4-2.1 kPa). If not, check the throttle plate for correct position or check the port for obstruction.
  6.  
  7. Connect a vacuum gauge between the vacuum amplifier and the temperature valve.
  8.  
  9. Replace the vacuum amplifier if the gauge reads less than 2 in. Hg. (14 kPa).
  10.  

REMOVAL & INSTALLATION



EGR Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the vacuum hose from the EGR valve.
  4.  
  5. Unbolt the EGR line fitting on the opposite side of the valve.
  6.  
  7. Remove the two retaining bolts and lift the EGR valve from the intake manifold.
  8.  

To install:
  1. Install the EGR valve with a new gasket. Tighten the bolts to 7 ft. lbs. (10 Nm).
  2.  
  3. Connect the vacuum hose to the EGR valve.
  4.  
  5. Connect the battery cable.
  6.  

EGR Filter
  1. Disconnect the EGR filter line fittings.
  2.  
  3. Remove the filter and discard.
  4.  

To install:
  1. Position the new filter into the EGR lines, then securely tighten the fittings.
  2.  

Temperature Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Label and disconnect the vacuum hoses from the valve.
  4.  
  5. Remove the valve using a wrench or deep socket.
  6.  

To install:
  1. Thread the valve in by hand, then tighten until snug.
  2.  
  3. Connect the hoses to the valve.
  4.  
  5. Connect the battery cable.
  6.  

 
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