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

Pulsed Secondary Air Injection

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OPERATION



See Figure 1

The air injection system is used to inject fresh air into the exhaust manifolds or catalytic converters via an air control valve. The air is created by a air pump that is driven by the engine, it is located in the front of the engine and is propelled by a belt.

The system uses a shut-off valve which is used to prevent backfire in the exhaust system during sudden deceleration. When the throttle is suddenly closed, a too-rich air/fuel mixture may be created which could not normally be burned. This mixture becomes burnable when it reaches the exhaust area and combines with the injected air. The shut-off valve senses the sudden increase in the intake manifold vacuum causing the valve to open, allowing air from the air pump to pass through the valve and silencer into the atmosphere.



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Fig. Fig. 1: Pulsed Secondary Air System

COMPONENT TESTING



Do not attempt to correct pump noise by lubricating the air pump. Never lubricate the air pump. Do not assume a pump is bad just because it's noisy.

Control Valve Functional Test
  1. Run the engine to normal operating temperature, then increase the speed to 1,500 rpm.
  2.  
  3. Disconnect the vacuum hose at the valve inlet and verify that there is vacuum present.
  4.  
  5. With the engine running at 1,500 rpm, airflow should be felt and heard at the outlet side of the shut-off valve.
  6.  
  7. If the valve is not functioning properly, replace it.
  8.  

Air Supply Pump Functional Check
  1. Check and, if necessary, adjust the belt tension. Press at the mid-point of the belt's longest straight run. You should be able to depress the belt about 1 / 2 in. (13mm) at most.
  2.  
  3. Run the engine to normal operating temperature and let it idle.
  4.  
  5. Disconnect the air supply hose from the shut-off valve. If the pump is operating properly, airflow should be felt at the hose. The flow should increase as you increase the engine speed. The pump is not serviceable and should be replaced if it is not functioning properly.
  6.  

REMOVAL & INSTALLATION



Air Pump
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the drive belt.
  4.  
  5. Remove the air hose from the air pump.
  6.  
  7. Remove the pivot and adjusting bolts from the pump and bracket.
  8.  
  9. Remove the pump from the vehicle.
  10.  

To install:
  1. Install the pump on the mounting bracket and tighten the bolts.
  2.  
  3. Install the air hose onto the pump control valve.
  4.  
  5. Install and adjust the drive belt.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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