Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Air Injection (AI) System

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OPERATION



See Figures 1 and 2

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Fig. Fig. 1: Air injection system components



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Fig. Fig. 2: Cutaway view of an air suction solenoid

The Air Injection (AI) system utilizes the vacuum created by exhaust gas pulsation and normal intake manifold vacuum. Each exhaust port is connected to the air suction valve by air suction manifolds. When a vacuum is created in the exhaust ports, a reed in the suction valve opens allowing fresh air to be sucked into the exhaust ports. When there is pressure rather than vacuum in the exhaust ports, the reed in the air suction valve closes, preventing the flow of exhaust gases.

The fresh air sucked through the air suction valve is used for oxidation of HC and CO in the exhaust passages and partly for combustion in the cylinders

The system incorporates an electronically controlled solenoid that either deactivates this system entirely, or partially a short time after the engine is started cold. The only way to determine that there is a problem with this system is to remove the solenoid and test it electrically.

Models equipped with an AI system incorporate an Air Suction Valve (ASV), which can be disassembled and serviced.

Various models have an exhaust port liner made from stainless steel plate built into the cylinder head as one unit. The port liner has a built in air layer which decreases heat transfer to the cylinder head while keeping the exhaust port at a higher temperature. The insulation of the exhaust port helps oxidation of residual HC and CO with the help of the remaining air in the exhaust gases.

The anti-afterburn valve prevents afterburning that occurs on cold starts. Below 122°F (50°C), the temperature valve has an open passage connecting the afterburning valve with the intake manifold via a vacuum line. The vacuum line remains opened, and the afterburning valve in operation until the coolant temperature becomes hot enough to shut off the vacuum and override the afterburning system.

TESTING



Air Suction Valve
  1. Remove the air suction valve assembly.
  2.  
  3. Blow air through the air inlet to see if air flows smoothly through the outlet while emitting a hissing sound. If air does not flow smoothly, the read valve could be stuck closed. Replace the reed valve.
  4.  
  5. Blow air through the outlet side of the valve to see if air flows through the inlet. If air flows, the reed valve is broken or stuck open. Replace the reed valve.
  6.  
  7. Check the valve after it has been disassembled. To disassemble, proceed as follows:
    1. Check the inlet and outlet case for cracks or damage.
    2.  
    3. Check the gasket for cracks or damage.
    4.  
    5. Clean the reed valve thoroughly.
    6.  
    7. Check for check for waves, cracks or dents in the seat.
    8.  
    9. Check the reed for cracks or a broken point.
    10.  
    11. Check the valve for a rusty stopper.
    12.  
    13. Replace any broken or damaged part.
    14.  

  8.  

Air Suction Solenoid
  1. Remove the solenoid electrical harness.
  2.  
  3. Check the resistance between the positive and negative terminals. Resistance should be 33-40 ohms.
  4.  
  5. Check the resistance between the positive or negative terminals, and the solenoid body. Resistance should be at least 1M ohm.
  6.  
  7. Check the vacuum passage for opening and closing operation while applying battery voltage to the positive and negative terminals.
  8.  
  9. If the solenoid does not function as specified, replace the solenoid.
  10.  

REMOVAL & INSTALLATION



Air Suction Valve
  1. Remove the air silencer or secondary air cleaner assembly from the engine.
  2.  
  3. Remove the four bolts which run through the air suction valve, mounting it between the two air suction manifolds.
  4.  
  5. Pull the suction valve from between the manifolds. Take care not to damage the reeds.
  6.  

If the gaskets on the sides of the air suction valve are worn or damaged, replace them.

To install:
  1. Using new gaskets install the air suction valve and tighten the bolts securely.
  2.  
  3. Install the air silencer or secondary air cleaner.
  4.  

OVERHAUL
  1. Remove the three retainer screws, and separate the control valve assembly, seat, and reed valve cover.
  2.  
  3. Separate the reed valve assembly by pulling it and the gasket from the inside of the valve cover.
  4.  
  5. Remove the O-ring from the control valve assembly.
  6.  
  7. Inspect the valve parts as follows:
    1. Apply vacuum to the vacuum inlet. The valve should retract fully. Release the vacuum. The valve should extend fully.
    2.  
    3. Check the O-ring for cracks or other damage.
    4.  
    5. Inspect the reed valve gasket for damage. Then, clean the reed valve in a safe, non-volatile solvent and inspect it for any damage such as waviness, cracks, dents, or rust.
    6.  

  8.  
  9. Replace all damaged or worn parts.
  10.  

To assemble:
  1. Install the O-ring on the control valve assembly.
  2.  
  3. Join the reed valve assembly making sure the gasket stays inside of the valve cover.
  4.  
  5. Install the three screws, joining the control valve assembly, seat, and reed valve cover.
  6.  

Air Suction Manifolds
  1. Remove the air silencer or secondary air cleaner and the air suction valve from the engine compartment.
  2.  
  3. Remove the clamp which supports the right side suction manifold by loosening the mounting bolt.
  4.  
  5. Loosen the threaded sleeves (two on each manifold), which mount the suction manifolds to the engine. Lift off the manifolds.
  6.  

To install:
  1. Lightly oil the threaded sleeves before mounting the suction manifold to the engine.
  2.  
  3. Install the manifolds and tighten the sleeves securely.
  4.  
  5. Install the clamp which supports the right side suction manifold.
  6.  
  7. Install the air silencer or secondary air cleaner and the air suction valve.
  8.  

 
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