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

Air Injection System

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ff-1, 200G AND ALL 375 MODELS



An air injection system is used on ff-1, 200G and all 375 models

A belt driven air pump is used to supply air, under pressure, to air distribution manifolds which have openings at each exhaust port. Injection of air at this point causes combustion of the unburned hydrocarbons in the exhaust manifolds, rather than allowing them to escape into the atmosphere. An anti-backfire valve controls the flow of air from the pump to prevent backfiring which results from an overly rich mixture under closed throttle conditions.

Check valves prevent hot exhaust gas backflow into the pump and hoses in case of pump failure or when the anti-backfire valve is not working.

Air pumps are equipped with a relief valve to discharge excess air which the pump produces at high engine speed.

On 200G models, an additional air by-pass valve is used. When the manual choke is pulled out, the air by-pass causes the air from the pump to flow into the air cleaner rather than the exhaust manifolds, which prevents the manifolds from being overheated.



Click image to see an enlarged view

Fig. Fig. 1 1300G air injection system-ff-1 and 1975 models similar

REMOVAL & INSTALLATION



Air Pump
  1. Disconnect the air hoses from the pump.
  2.  
  3. Loosen the bolt on the adjusting link and remove the drive belt.
  4.  
  5. Remove the mounting bolts and remove the pump.
  6.  


CAUTION
Do not pry on the pump housing. It may become distorted.

To install:

  1. Install the pump, fasten the mounting bolts and fasten the bolt on the adjusting link. Connect the hoses.
  2.  
  3. Adjust the drive belt tension. Belt deflection should be 3.5 in. (9mm) with 22 lbs. (29 Nm) pressure.
  4.  



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Fig. Fig. 2 Components of the air injection system

Anti-Backfire Valve
  1. Detach the air hoses from the valve.
  2.  
  3. Remove the valve securing bolt.
  4.  
  5. Remove the valve.
  6.  
  7. Installation is the reverse of removal.
  8.  

Check Valves
  1. Detach the intake hoses from the valves.
  2.  
  3. Use an open end wrench to remove the valve from its mounting. Be sure to save the aluminum gasket.
  4.  

Relief Valve
  1. Remove the air pump from the car.
  2.  
  3. Support the pump so that it cannot rotate.
  4.  


CAUTION
Never clamp the pump in a vise. The aluminum case will be distorted.

  1. Remove the relief valve from the top of the pump.
  2.  

To install:

  1. Position the new relief valve over the opening in the pump.
  2.  


WARNING
The air outlet should be pointing toward the left.

  1. Gently tap the relief valve home, using a block of wood and a hammer.
  2.  
  3. Install the pump on the engine, as outlined above.
  4.  

Air Injection Manifold
  1. Remove the check valve, as outlined above.
  2.  
  3. Detach the air supply hose from the check valve.
  4.  
  5. Remove the manifold.
  6.  

Air By-pass Valve (371-72 EA62 Only)
  1. Disconnect the hoses from the air by-pass valve.
  2.  
  3. Detach the cable from the valve butterfly operating lever.
  4.  
  5. Remove the valve.
  6.  

TESTING



Belt Tension and Air Leaks
  1. Before proceeding with the tests, check the pump drive belt tension to see if it is within specifications.
  2.  
  3. Turn the pump by hand. If it has seized, the belt will slip, making a noise. Disregard any chirping, squealing, or rolling sounds from inside the pump. These are normal when it is turned by hand.
  4.  
  5. Check the hoses and connections for leaks. Hissing or a blast of air is indicative of a leak. Soapy water, applied lightly around the area in question, is a good method for detecting leaks.
  6.  



Click image to see an enlarged view

Fig. Fig. 3 Troubleshooting the air injection system

Air Output
  1. Disconnect the air supply hose at the anti-backfire valve.
  2.  
  3. Connect a vacuum gauge, using a suitable adaptor, to the air supply hose.
  4.  


WARNING
If there are two hoses, plug the second one.

  1. With the engine at normal operating temperature, increase the idle speed and watch the vacuum gauge.
  2.  
  3. The air flow from the pump should be steady and fall between 1.5-6 psi (10-41 kPa). If it is unsteady or falls below this, the pump is defective and must be replaced.
  4.  

Pump Noise Diagnosis

The air pump is normally noisy. As engine speed increases, the noise of the pump will rise in pitch. The rolling sound the pump bearings make is normal. But if this sound becomes objectionable at certain speeds, the pump is defective and will have to be replaced.

A continual hissing sound from the air pump pressure relief valve at idle, indicates a defective valve. Replace the relief valve.

If the pump rear bearing fails, a continual knocking sound will be heard.

Anti-Backfire Valve
  1. Detach the air supply hose which runs between the pump and the gulp valve.
  2.  
  3. Connect a tachometer and run the engine to 1500-2000 rpm.
  4.  
  5. Allow the throttle to snap closed. This should produce a loud sucking sound from the gulp valve.
  6.  
  7. Repeat this operation several times. If no sound is present, the valve is not working, or the vacuum connections are loose.
  8.  

Check Valve Test
  1. Before starting the test, check all of the hoses and connections for leaks.
  2.  
  3. Detach the air supply hose from the check valve.
  4.  
  5. Insert a suitable probe into the check valve and depress the plate. Release it. The plate should return to its original position against the valve seat. If binding is evident, replace the valve.
  6.  
  7. With the engine running at normal operating temperature, gradually increase its speed to 1500 rpm. Check for exhaust gas leakage. If any is present, replace the valve assembly.
  8.  

Air By-pass valve (EA62 Only)

Check the air by-pass valve to be sure that it is open when the choke is closed.

If the by-pass valve is not operating in this manner, adjust its operating cable.

 
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