Subaru ff-1/1300/1400/1600/1800/Brat 1970-1984 Repair Guide

Air Suction System

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OPERATION



The air suction system is very similar to the air injection system, except it does not use an air pump. It is used on 1976-84 models.

To operate, the 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 through the air cleaner and silencer (1976-79 models) or the secondary air cleaner (1980-84 models) and 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

1982-84 models incorporate 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. See the test procedure below.

These models also incorporate an Air Suction Valve which can be disassembled and serviced. See the procedure below for service.



Click image to see an enlarged view

Fig. Fig. 1 Exploded view of the air suction system

Port Liner

Various models from 1980-84 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.

Anti-afterburning Valve

The anti-afterburning valve prevents afterburning that occurs on cold starts. Below about 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.

REMOVAL & INSTALLATION



Silencer
  1. Loosen the sleeve nut which mounts the silencer to the top of the air suction valve.
  2.  
  3. Pull the silencer from the hose connecting it to the air cleaner.
  4.  


WARNING
Be careful not to lose the small tapered sleeve below the sleeve nut when lifting off the silencer.

  1. Installation is the reverse of removal.
  2.  

Secondary Air Cleaner

On late model EA71 and EA81 engines, the air flowing to the air suction valve passes through a secondary air cleaner instead of the carburetor air cleaner and silencer. Do not attempt to clean the filter element. Replace the cleaner element every 30 months or 30,000 miles (48,000 km), whichever occurs first.



Click image to see an enlarged view

Fig. Fig. 2 Air suction system with a secondary air cleaner

Air Suction Valve
  1. Remove the air silencer or secondary air cleaner.
  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.  


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

Air Suction Manifolds
  1. Remove the air silencer or secondary air cleaner and the air suction valve.
  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.  
  7. Remember to lightly oil the threaded sleeves before mounting the suction manifold to the engine.
  8.  



Click image to see an enlarged view

Fig. Fig. 3 Solenoid valve for the 1982-84 air suction systems. See text for a description of which passages (A, B, C) are open under various conditions

TESTING



Solenoid Valve (1982-84 Only)
  1. Remove the valve from the engine. Using an ohmmeter, test the resistance between the electrical terminals. It must be 32.7-39.9 ohms. If not, replace it.
  2.  
  3. If resistance is o.k., check the resistance between each terminal and the solenoid body. It must be 1,000 ohms. or more in both places, or the valve should be replaced.
  4.  
  5. Apply 12 volts between the plus and minus terminals (positive battery terminal to positive solenoid terminal). When current is on, you should be able to blow through the solenoid from A to B. When it is off, it must seal off tight from A to B and open from B to C. Otherwise, replace the solenoid.
  6.  

DISASSEMBLY



Air Suction Valve (1982-87 only)
  1. Remove the three screws, and separate the control valve assembly, seat, and reed valve cover.
  2.  
  3. Separate the reed valve assembly by pulling it and its gasket from the inside of the valve cover.
  4.  
  5. Remove the O-ring from the control valve assembly.
  6.  
  7. Now, inspect the valve parts as follows:
  8.  
    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 or dents, or rust.
    6.  

  9. Replace parts that are damaged, reassemble the valve in reverse order, and reinstall it.
  10.  



Click image to see an enlarged view

Fig. Fig. 4 Parts of the reed valve assembly-1982-84 models

 
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