GM Full-Size Trucks 1988-1998 Repair Information

Air Injector Reactor (AIR) System

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OPERATION



The AIR system injects compressed air into the exhaust system, near enough to the exhaust valves to continue the burning of the normally unburned segment of the exhaust gases. To do this, it employs an air injection pump and a system of hoses, valves, tubes, etc., necessary to carry the compressed air from the pump to the exhaust manifolds.

A diverter valve is used to prevent backfiring. The valve senses sudden increases in manifold vacuum and ceases the injection of air during rich periods. During coasting, this valve diverts the entire air flow through a muffler and during high engine speeds, expels it through a relief valve. Check valves in the system prevent exhaust gases from entering the pump.

TESTING



The A.I.R. system is not completely silent under normal conditions. Noises will rise in pitch as engine speed increases. If the noise is excessive, eliminate the air pump itself by disconnecting the drive belt. If the noise disappears, the air pump is not at fault.

Check Valve

To test the check valve, disconnect the hose at the diverter valve. Place your hand over the check valve and check for exhaust pulses. If exhaust pulses are present, the check valve must be replaced.

Diverter Valve

Pull off the vacuum line to the top of the valve with the engine running. There should be vacuum in the line, if not replace the line. No air should be escaping with the engine running at a steady idle. Open and quickly close the throttle. A blast of air should come out of the valve muffler for at least one second.

Air Pump

Disconnect the hose from the diverter valve. Start the engine and accelerate it to about 1500 rpm. The air flow should increase as the engine is accelerated. If no air flow is noted or it remains constant, check the following:

  1. Drive belt tension.
  2.  
  3. Listen for a leaking pressure relief valve. If it is defective, replace the whole relief/diverter valve.
  4.  
  5. Foreign matter in pump filter openings. If the pump is defective or excessively noisy, it must be replaced.
  6.  

REMOVAL & INSTALLATION



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: AIR system components

All hoses and fittings should be inspected for condition and tightness of connections. Check the drive belt for wear and tension periodically.

Air Pump
  1. Disconnect the output hose.
  2.  
  3. Hold the pump from turning by squeezing the drive belt.
  4.  
  5. Loosen, but do not remove, the pulley bolts.
  6.  
  7. Loosen the alternator so the belt can be removed.
  8.  
  9. Remove the pulley.
  10.  
  11. Remove the pump mounting bolts and the pump.
  12.  

To install:
  1. Install the pump with the mounting bolts loose.
  2.  
  3. Install the pulley and tighten the bolts finger-tight.
  4.  
  5. Install the drive belt.
  6.  
  7. Squeeze the drive belt to prevent the pump from turning.
  8.  
  9. Tighten the pulley bolts to 25 ft. lbs. (33 Nm). Tighten the pump mountings.
  10.  
  11. Check and adjust the belt tension.
  12.  
  13. Connect the hose.
  14.  
  15. If any hose leaks are suspected, pour soapy water over the suspected area with the engine running. Bubbles will form wherever air is escaping.
  16.  

Filter

See Figure 2

  1. Remove the pump and the diverter valve as an assembly.
  2.  


WARNING
Do not clamp the pump in a vise or use a hammer or pry bar on the pump housing! Damage to the housing may result.

  1. To change the filter, break the plastic fan from the hub. It is seldom possible to remove the fan without breaking it. Wear safety glasses.
  2.  
  3. Remove the remaining portion of the fan filter from the pump hub. Be careful that filter fragments do not enter the air intake hole.
  4.  

To install:
  1. Position the new centrifugal fan filter on the pump hub. Place the pump pulley against the fan filter and install the securing screws. Tighten the screws alternately to 95 inch lbs. (10 Nm). The fan filter will be pressed onto the pump hub.
  2.  
  3. Install the pump on the engine and adjust the drive belt.
  4.  



Click image to see an enlarged view

Fig. Fig. 2: Air pump filter removal

 
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