GM Full-Size Trucks 1970-1979 Repair Guide

Air Injection Reactor (AIR) System

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See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Air Injector Reactor (AIR) system operation



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Fig. Fig. 2: Air pump mounting - inline 6-cylinder engines shown



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Fig. Fig. 3: Air pump system components - V8 engine shown



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Fig. Fig. 4: AIR system component locations - 1978 C/K series 350 and 400 engines shown

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. Carburetors and distributors for AIR engines have specific modifications to adapt them to the air injection system. These components should not be interchanged with those intended for use on engines that do not have the system.

A diverter valve is used to prevent backfiring. The valve senses sudden increases in manifold vacuum and ceases the injection of air during fuel-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



Check Valve

To test the check valve, disconnect the hose at the diverter valve. Blow into the hose and suck on it. Air should flow only into the engine.

Diverter Valve

Pull off the vacuum line to the top of the valve with the engine running. There should be vacuum in the line. 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. If the valve must be replaced, use a new gasket at the valve mounting on the pump and torque the bolts to 85 inch lbs. (9.5 Nm).

Air Pump

Disconnect the hose from the diverter valve. Start the engine and accelerate it to about 1,500 rpm. The airflows should increase as the engine is accelerated. If no airflow 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.  

SERVICE



The AIR system's effectiveness depends on correct engine idle speed, ignition timing, and dwell. These settings should be strictly adhered to and checked frequently. All hoses and fittings should be inspected for condition and tightness of connections. Check the drive belt for wear and tension every 12 months or 12,000 miles (4 months/6,000 miles on 1974-75 models). If, after completion of a tune-up and/or individual inspection of components, a malfunction still exists, the vehicle should be serviced by qualified mechanics.

The AIR system is not completely noiseless. Under normal conditions, noise rises in pitch as engine speed increases. To determine if excessive noise is the fault of the AIR system, operate the engine with the pump drive belt removed. If the noise does not exist with the belt removed:

  1. Check for a seized pump.
  2.  
  3. Check hoses, tubes and connections for leaks or kinks.
  4.  
  5. Check the diverter valve.
  6.  
  7. Check the pump for proper mounting.
  8.  


WARNING
Do not oil the AIR pump.

If no irregularities exist and the AIR pump noise is still excessive, replace the pump.

REMOVAL & INSTALLATION



Air Pump

WARNING
Do not pry on the pump housing or clamp the pump in a vise: the housing is soft and may become distorted.

  1. Disconnect the air hoses at the pump.
  2.  
  3. Hold the pump pulley from turning and loosen the pulley bolts.
  4.  
  5. Loosen the pump mounting bolt and adjustment bracket bolt. Remove the drive belt.
  6.  
  7. Remove the mounting bolts, and then remove the pump.
  8.  
  9. Installation of the pump is the reverse of the removal procedure.
  10.  

Pump Filter

See Figure 5



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Fig. Fig. 5: The AIR pump filter can be removed with needle-nosed pliers

  1. Remove the drive belt and pump pulley.
  2.  
  3. Using needle-nosed pliers, pull the fan from the pump hub.
  4.  


WARNING
Use care to prevent any dirt or fragments from entering the air intake hole. DO NOT insert a screwdriver between the pump and the filter, and do not attempt to remove the metal hub. It is seldom possible to remove the filter without destroying it.

To install:
  1. To install a new filter, draw it on with the pulley and pulley bolts. Do not hammer or press the filter on the pump.
  2.  
  3. Draw the filter down evenly by torquing the bolts alternately. Make sure the outer edge of the filter slips into the housing. A slight amount of interference with the housing bore is normal.
  4.  

The new filter may squeal initially until the sealing lip on the pump outer diameter has worn in.

Diverter Valve

See Figure 6



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Fig. Fig. 6: Cross-sectional view of the diverter valve

  1. Detach the vacuum sensing line from the valve.
  2.  
  3. Remove the other hose(s) from the valve.
  4.  
  5. Unfasten the diverter valve from the elbow or the pump body.
  6.  

Installation is performed in the reverse order of removal. Always use a new gasket. Tighten the valve securing bolts to 85 inch lbs. (9.5 Nm).

 
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