A belt-driven pump supplies air to an injection manifold which has nozzles in each exhaust port. Injection of air at this point causes combustion of unburned hydrocarbons in the exhaust manifold 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. There are two types of antibackfire valve used on Toyota models: 1970-71 models use gulp valves; 1972-82 models air bypass valves.
A check valve prevents hot exhaust gas backflow into the pump and hoses, in case of a pump failure, or when the antibackfire valve is not working.
In addition, all 1975-82 engines have an Air Switching Valve (ASV). On engines without catalytic converters, the ASV is used to stop air injection under a constant heavy engine load condition.
On engines with catalytic converters, the ASV is also used to protect the catalyst from overheating, by blocking the injector air necessary for the operation of the converter.
Since 1975 on most passenger car engines, the pump relief valve is built into the ASV.
REMOVAL & INSTALLATION
- Disconnect the air hoses from the pump.
- Loosen the bolt on the adjusting link and remove the drive belt.
- Remove the mounting bolts and withdraw the pump.
- Installation is in the reverse order of removal. Adjust the drive belt tension after installation. Belt deflection should be 1 / 2 - 3 / 4 inch with 22 lbs. pressure.
- Detach the air hoses from the valve, and electrical leads (if equipped).
- Remove the valve securing bolt.
- Withdraw the valve.
- Installation is performed in the reverse order of removal.
- Detach the intake hose from the valve.
- Use an open-end wrench to remove the valve from its mounting.
- Installation is the reverse of removal.
From 1975 on models with ASV-mounted relief valves, replace the entire ASV/relief valve as an assembly.
- Remove the air pump from the car.
- Support the pump so that it cannot rotate.
- Use a bridge to remove the relief valve from the top of the pump.
- Position the new relief valve over the opening in the pump.
The air outlet should be pointing toward the left.
- Gently tap the relief valve home, using a block of wood and a hammer.
- Install the pump on the engine, as outlined above.
- Remove the check valve, as previously outlined.
- Loosen the air injection manifold attachment nuts and withdraw the manifold.
On some engines it may be necessary to remove the exhaust manifold first.
- Installation is in the reverse order of removal.
- Remove the air injection manifold as previously outlined.
- Remove the cylinder head, as detailed in .
- Place a new nozzle on the cylinder head.
- Install the air injection manifold over it.
- Install the cylinder head on the engine block.
BELT TENSION AND AIR LEAKS
- Before proceeding with the tests, check the pump drive belt tension to ensure that it is within specifications.
- Turn the engine. If the pump 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.
- Check the hoses and connections for leaks. Hissing or a blast of air indicates a leak. Soapy water, applied lightly around the area in question, is a good method for detecting leaks.
- Disconnect the air supply hose at the anti-backfire valve.
- Connect a vacuum gauge, using a suitable adaptor, to the air supply hose.
If there are two hoses, plug the second one.
- With the engine at normal operating temperature, increase the idle speed and watch the vacuum gauge.
- The airflow from the pump should be steady (between 2 and 6 psi). If it is unsteady or falls below specs, the pump is defective and must be replaced.
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. Since the rear bearing is not separately replaceable, the pump will have to be replaced as an assembly.Anti-Backfire Valve
There are two different types of anti-backfire valve used with air injection systems. A bypass valve is used on 1971-82 engines, while 1970-71 engines use a gulp type anti-backfire valve. Test procedures for both types are given below.GULP VALVE
- Detach the air supply hose which runs between the pump and the gulp valve.
- Connect a tachometer and run the engine to 1,500-2,000 rpm.
- Allow the throttle to snap shut. This should produce a loud sucking sound from the gulp valve.
- Repeat this operation several times. If no sound is present, the valve is not working or else the vacuum connections are loose.
- Check the vacuum connections. If they are secure, replace the gulp valve.
- Detach the hose, which runs from the bypass valve to the check valve, at the bypass valve hose connection.
- Connect a tachometer to the engine. With the engine running at normal idle speed, check to see that air is flowing from the by-pass valve hose connection.
- Speed up the engine so that it is running at 1,500-2,000 rpm. Allow the throttle to snap shut. The flow of air from the bypass valve at the check valve hose connection should stop momentarily and air should then flow from the exhaust port on the valve body or the silencer assembly.
- Repeat Step 3 several times. If the flow of air is not diverted into the atmosphere from the valve exhaust port or if it fails to stop flowing from the hose connection, check the vacuum lines and connections. If these are tight, the valve is defective and requires replacement.
- A leaking diaphragm will cause the air to flow out both the hose connection and the exhaust port at the same time. If this happens, replace the valve.
- Before starting the test, check all of the hoses and connections for leaks.
- 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