GM Full Size Vans 1987-1997 Repair Guide

Air Injector Reactor (AIR) System


See Figures 1 through 5

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Fig. Fig. 1: Air control valve - 4.3L California carbureted engine

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Fig. Fig. 2: Deceleration control valve airflow

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Fig. Fig. 3: AIR system schematic - 7.4L TBI engine shown; 4.3L and 5.7L engines similar

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Fig. Fig. 4: Electric air control valve - 4.3L TBI engine

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Fig. Fig. 5: AIR system components

The AIR system injects compressed air into the exhaust system, close enough to the exhaust valves to continue burning the normally unburned segment of the exhaust gases. To do this, the AIR system 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.


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

Check Valve

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

Diverter Valve

See Figure 6

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Fig. Fig. 6: Diverter valve - 4.3L 49 states carbureted engine

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:

Drive belt tension.
Leaking pressure relief valve. If defective, replace the entire relief/diverter valve.
Foreign matter in pump filter openings. If the pump is defective or excessively noisy, it must be replaced.


See Figures 7 and 8

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Fig. Fig. 7: AIR pump mounting

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Fig. Fig. 8: Deceleration valve mounting

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.
  3. Hold the pump from turning by pressing the drive belt.
  5. Loosen, but do not remove, the pulley bolts.
  7. Loosen the alternator so the belt can be removed.
  9. Remove the pulley.
  11. Remove the pump mounting bolts and the pump.

To install:
  1. Install the pump with the mounting bolts loose.
  3. Install the pulley and tighten the bolts finger-tight.
  5. Install the drive belt.
  7. Press the drive belt to prevent the pump from turning.
  9. Tighten the pulley bolts to 25 ft. lbs. (33 Nm). Tighten the pump mountings.
  11. Check and adjust the belt tension.
  13. Connect the hose.
  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.


See Figure 9

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Fig. Fig. 9: AIR pump filter removal