GM Full Size Vans 1987-1997 Repair Guide

Air Management System

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The Air Management System is used to provide additional oxygen to continue the combustion process after the exhaust gases leave the combustion chamber, much the same as the AIR system described earlier in this section. Air is injected into either the exhaust port(s), the exhaust manifold(s) or the catalytic converter by an engine driven air pump. The system is in operation at all times and will bypass air only momentarily during deceleration and at high speeds. The bypass function is performed by the Air Management Valve, a check valve which protects the air pump by preventing any backflow of exhaust gases.

The Air Management System helps to reduce HC and CO content in the exhaust gases by injecting air into the exhaust ports during cold engine operation. This air injection also helps the catalytic converter to reach the proper temperature quicker during warm-up. When the engine is warm (closed loop), the Air Management System injects air into the beds of a 3-way converter to lower the HC and CO content in the exhaust.

The Air Management System utilizes the following components:

  1. An engine driven air pump.
  2.  
  3. Air management valves (Air Control and Air Switching)
  4.  
  5. Air flow and control hoses
  6.  
  7. Check valves
  8.  
  9. A dual bed, 3-way catalytic converter
  10.  

The belt driven, vane type air pump is located at the front of the engine and supplies clean air to the system for purposes already stated. When the engine is cold, the Electronic Control Module (ECM) energizes an air control solenoid. This allows air to flow to the air switching valve. The air switching valve is then energized to direct air into the exhaust ports.

When the engine is warm, the ECM de-energizes the air switching valve, thus directing air between the beds of the catalytic converter. This air then provides additional oxygen for the oxidizing catalyst in the second bed to decrease HC and CO levels, while at the same time keeping oxygen levels low in the first bed, enabling the reducing catalyst to effectively decrease the levels of NOx.

If the air control valve detects a rapid increase in manifold vacuum (deceleration), certain operating modes (wide open throttle, etc.) or if the ECM self-diagnostic system detects any problems in the system, air is diverted to the air cleaner or directly into the atmosphere.

The primary purpose of the ECM's divert mode is to prevent backfiring. Throttle closure at the beginning of deceleration will temporarily create air/fuel mixtures which are too rich to burn completely. These mixtures will become burnable when they reach the exhaust if they are combined with injection air. The next firing of the engine will ignite the mixture causing an exhaust backfire. Momentary diverting of the injection air from the exhaust prevents this.

The Air Management System check valves and hoses should be checked periodically for any leaks, cracks or deterioration.

TESTING



See Figure 1

Refer to the accompanying flow chart when testing the Air Management System.



Click image to see an enlarged view

Fig. Fig. 1: Air Management System diagnostic chart

REMOVAL & INSTALLATION



Air Pump
  1. Remove the valves and/or adapter at the air pump.
  2.  
  3. Loosen the air pump adjustment bolt and remove the drive belt.
  4.  
  5. Unscrew the three mounting bolts and then remove the pump pulley.
  6.  
  7. Unscrew the pump mounting bolts and then remove the pump.
  8.  
  9. Installation is in the reverse order of removal. Be sure to adjust the drive belt tension after installing it.
  10.  

Check Valve
  1. Release the clamp and disconnect the air hoses from the valve.
  2.  
  3. Unscrew the check valve from the air injection pipe.
  4.  
  5. Installation is in the reverse order of removal.
  6.  

Air Management Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner.
  4.  
  5. Tag and disconnect the vacuum hose from the valve.
  6.  
  7. Tag and disconnect the air outlet hoses from the valve.
  8.  
  9. Bend back the lock tabs and then remove the bolts holding the elbow to the valve.
  10.  
  11. Tag and disconnect any electrical connections at the valve, then remove the valve from the elbow.
  12.  
  13. Installation is in the reverse order of removal.
  14.  

 
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