Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Air Injection/Air Suction Systems

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OPERATION



The air injection system is used on carbureted engines, except 1978 and 1980 models with 34 PICT-5 carburetors and later models equipped with a Carter TYF carburetor. This system includes a belt driven air pump, filter, check valve, anti-backfire valve (or gulp valve), and connecting hoses. Reduction of exhaust emissions is achieved by pumping fresh air to the exhaust manifold or directly behind the exhaust valves where it combines with the hot exhaust gas to burn away excess hydrocarbons and reduce carbon monoxide.

The air suction system used on 1978 and later carbureted models does not utilize an air pump. Instead, air is drawn from the air cleaner through a silencer and into two check valves. This system uses the same principle as the air injection system to reduce emissions.

TESTING



Air Pump and Hoses

See Figure 1

  1. Disconnect the hose from the check valve and plug the valve opening.
  2.  
  3. With the engine idling, check for air flow from the hose (make sure the hoses are not kinked or damaged). If no air flows from the hose, either the diverter valve or the air pump is defective. These cannot be repaired, only replaced.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Disconnect the hose from the check valve, then plug the valve opening

Anti-Backfire Valve

See Figure 2

A defective anti-backfire valve could be indicated by the engine backfiring while coasting.

  1. Disconnect the bottom hose from the valve.
  2.  



Click image to see an enlarged view

Fig. Fig. 2: Disconnect the bottom hose from the anti-backfire valve

  1. Start the engine and run it briefly at higher than normal fast idle.
  2.  
  3. Snap the throttle valve closed. As the throttle snaps shut, suction should be felt at the valve for about 1-3 seconds. If not, the hoses could be kinked/blocked or the valve is defective.
  4.  

Check Valves

See Figure 3

On air injection systems, disconnect the hose from the check valve. Start the engine. If you feel exhaust gases coming out of the check valve, it must be replaced.

On air suction systems, if the check valves are discolored with a blue tint, they must be replaced. This condition indicates that the valves were overheated due to the back-flow of exhaust gases.



Click image to see an enlarged view

Fig. Fig. 3: On air suction systems, if the check valves (arrows) turn blue, they must be replaced

REMOVAL & INSTALLATION



Air Pump
  1. Disconnect the negative battery cable.
  2.  
  3. Label and disconnect the hoses from the air pump.
  4.  
  5. Remove the air pump drive belt.
  6.  
  7. Loosen and remove the bolts securing the air pump.
  8.  
  9. Remove the pump from the vehicle.
  10.  

To install:
  1. Position the air pump, then install the mounting bolts finger-tight.
  2.  
  3. Install the drive belt and tighten the pump mounting bolts until snug.
  4.  
  5. Tension the belt, then tighten the lock bolt.
  6.  
  7. Connect the hoses to the air pump.
  8.  
  9. Connect the battery cable.
  10.  

Anti-Backfire Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Label and disconnect the hoses from the valve.
  4.  
  5. Remove the nuts/bolts securing the valve, then remove it from the vehicle.
  6.  

To install:
  1. Position the valve, then tighten the nuts/bolts until snug.
  2.  
  3. Connect the hoses to the valve.
  4.  
  5. Connect the battery cable.
  6.  

Check Valves
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the hoses from the check valves.
  4.  
  5. Loosen and remove the check valve. If the valve is difficult to remove, spray some penetrating oil on the threads and allow it to soak.
  6.  

To install:
  1. Thread the check valve in by hand first, then tighten until snug. Do not over-tighten the valve or the pipe could become distorted.
  2.  
  3. Connect the hoses to the check valve.
  4.  
  5. Connect the battery cable.
  6.  

 
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