Chrysler Full-Size Trucks 1989-1996 Repair Guide

Air Injection System

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OPERATION



See Figures 1, 2, 3 and 4

The air injection system is used to inject fresh air into the exhaust manifolds or catalytic converters via an air control valve. Under some operating conditions, the air can be dumped back into the atmosphere via an air bypass valve. On some applications the two valves are combined into one unit. The air bypass valve can be either the normally closed type, when the valves are separate, or the normally open type, when the valves are combined.

The system uses a diverter 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 diverter 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: Air injection system-V6 engine



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Fig. Fig. 2: A common air injection system-V8 engine shown, others similar

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.



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Fig. Fig. 3: A common air pump-3.9L model shown



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Fig. Fig. 4: Internal and external details of the diverter valve

COMPONENT TESTING



Normally Closed Air Bypass Valve Functional Test
  1. Disconnect the air supply hose at the valve.
  2.  
  3. Run the engine to normal operating temperature.
  4.  
  5. Disconnect the vacuum line and make sure vacuum is present. If no vacuum is present, remove or bypass any restrictors or delay valves in the vacuum line.
  6.  
  7. Run the engine at 1500 rpm with the vacuum line connected. Air pump supply air should be heard and felt at the valve outlet.
  8.  
  9. With the engine still at 1500 rpm, disconnect the vacuum line. Air at the outlet should shut off or dramatically decrease. Air pump supply air should now be felt or heard at the silencer ports.
  10.  
  11. If the valve doesn't pass each of these tests, replace it.
  12.  

Normally Open Air Bypass Valve Functional Test

  1. Disconnect the air supply hose at the valve.
  2.  
  3. Run the engine to normal operating temperature.
  4.  
  5. Disconnect the vacuum lines from the valve.
  6.  
  7. Run the engine at 1500 rpm with the vacuum lines disconnected. Air pump supply air should be heard and felt at the valve outlet.
  8.  
  9. Shut OFF the engine. Using a spare length of vacuum hose, connect the vacuum nipple of the valve to direct manifold vacuum.
  10.  
  11. Run the engine at 1500 rpm. Air at the outlet should shut off or dramatically decrease. Air pump supply air should now be felt or heard at the silencer ports.
  12.  
  13. With the engine still in this mode, cap the vacuum vent. Accelerate the engine to 2000 rpm and suddenly release the throttle. A momentary interruption of air pump supply air should be felt at the valve outlet.
  14.  
  15. If the valve doesn't pass each of these tests, replace it. Reconnect all lines.
  16.  

Air Control Valve Functional Test

  1. Run the engine to normal operating temperature, then increase the speed to 1500 rpm.
  2.  
  3. Disconnect the air supply hose at the valve inlet and verify that there is airflow present.
  4.  
  5. Reconnect the air supply hose.
  6.  
  7. Disconnect both air supply hoses.
  8.  
  9. Disconnect the vacuum hose from the valve.
  10.  
  11. With the engine running at 1500 rpm, airflow should be felt and heard at the outlet on the side of the valve, with no airflow heard or felt at the outlet opposite the vacuum nipple.
  12.  
  13. Shut OFF the engine.
  14.  
  15. Using a spare piece of vacuum hose, connect direct manifold vacuum to the valve's vacuum fitting. Airflow should be heard and felt at the outlet opposite the vacuum nipple, and no airflow should be present at the other outlet.
  16.  
  17. If the valve is not functioning properly, replace it.
  18.  

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 no more than 1 / 2 in. (4mm).
  2.  
  3. Run the engine to normal operating temperature and let it idle.
  4.  
  5. Disconnect the air supply hose from the bypass control valve. If the pump is operating properly, airflow should be felt at the pump outlet. 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 Injection Pump
3.9L, 5.9L AND 8.0L ENGINES
  1. Disconnect both of the hoses (tubes) at the air injection pump.
  2.  
  3. Loosen (but do not remove at this time) the air pump pulley mounting bolts.
  4.  
  5. Relax the belt tensioner and remove the belt.
  6.  
  7. Remove the air pump pulley bolts and remove the pulley from the pump.
  8.  
  9. Remove the two air pump mounting bolts and remove the pump from the bracket.
  10.  

To install:
  1. Position the air injection pump to the mounting bracket.
  2.  
  3. Install the pump mounting bolts, tightening them to 30 ft. lbs. (40 Nm).
  4.  
  5. Install the pump pulley and bolt it in place (only finger-tight for now).
  6.  
  7. Install the belt.
  8.  
  9. Tighten the pump pulley bolts to 9 ft. lbs. (2 Nm).
  10.  
  11. Install the hoses and hose clamps at the pump.
  12.  

Air Injection Pump Air Filter

8.0L ENGINE ONLY
  1. Remove the silencer tube at the housing.
  2.  
  3. Remove the air inlet tube at the housing.
  4.  
  5. Remove the rubber cap.
  6.  
  7. Remove the mounting bracket strap bolt.
  8.  
  9. Note the position of the tube fittings before removing the filter assembly from the bracket. Gently bend the strap and remove the filter assembly.
  10.  

To install:
  1. Install the filter assembly to the mounting bracket.
  2.  
  3. Install and tighten the strap bolt.
  4.  
  5. Install the rubber tubes and cap at the filter.
  6.  

 
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