See Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12
On 1975-81 engines, a belt-drive air 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 anti-backfire valve used: 1971 models use "gulp" valves; 1972-84 models "air by-pass" valves.
A check valve prevents hot exhaust gas backflow into the pump and hoses, in case of a pump failure, or when the anti-backfire 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 1975-81 engines with catalytic converters, the ASV is also used to protect the catalyst from overheating, by blocking the injected air necessary for the operation of the converter.
On all 1975-82 engines, the pump relief valve is build into the ASV.
On 1982 and later carbureted engines, the air injection system incorporates a "feedback" loop. An oxygen sensor threaded into the exhaust manifold monitors the oxygen concentration in the exhaust gas, and indirectly signals the air pump to divert compressed air to either the exhaust ports or the air cleaner, depending on the oxygen levels in the exhaust. On 1983 and later engines, an EACV (electronic air control valve) serves as gate keeper for the air flow according to engine temperature. The EACV takes the place of the ASV on earlier engines. Thus, the feedback system constantly readjusts itself in order to reduce hydrocarbon, carbon monoxide and nitrogen oxides in the exhaust. If the catalytic converter overheats during operation, a converter-mounted sensor will temporarily shut the air injection system off.
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.
Do not pry on the pump housing, it may be distorted.
- Installation is in the reverse order of removal. Adjust the drive belt tension after installation. Belt deflection should be 1 / 2 - 3 / 4 in. with 22 lbs. pressure.
- Remove the check valve, as previously outlined.
- Loosen the air injection manifold attachment nuts and withdraw the manifold.
On 20R engines, it will first be necessary to remove the exhaust manifold.
- Installation is in the reverse order of removal.
- Remove the air injection manifold as previously outlined.
- Remove the cylinder head, as detailed in Engine & Engine Overhaul .
- Place a new nozzle on the cylinder head.
- Install the air injection manifold over it.
- Install the cylinder head on the engine block.
Do not hammer, pry, or bend the pump housing while tightening the drive belt or testing the pump.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 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.
- 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.
- 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 air flow from the pump should be steady and fall between 2 and 6 psi. If it is unsteady or falls below this, the pump is defective and must be replaced.
See Figure 13
The air pump is normally noisy; as engine speed increases, the noise of the pump will rise in pitch. The rolling sound the pump bearing 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.
There are two different types of anti-backfire valve used with air injection systems. A by-pass valve is used in 1972-81 engines, while 1971 engines use a gulp type of 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 1500-2000 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 by-pass valve to the check valve, at the by-pass 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 1500-2000 rpm. Allow the throttle to snap shut. The flow of air from the by-pass 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.
See Figure 141975-78
- Before starting the test, check all of the hoses and connections for leaks.
- Detach the air supply hose from the check valve.
- 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.
- 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.
Vibration and flutter of the check valve at idle speed is a normal condition and does not mean that the valve should be replaced.1979-84
- Remove the check valve from the air injection manifold.
- Blow into the manifold side (large side) and check that the valve is closed.
- Blow into the ASV side (small side) and check that the valve is open.
- If the valve is not operating properly it will probably require replacement.
- Start the engine and allow it to reach normal operating temperature and speed.
- At curb idle, the air from the by-pass valve should be discharged through the hose which runs to the ASV.
- When the vacuum line to the ASV is disconnected, the air from the by-pass valve should be diverted out through the ASV-to-air cleaner hose. Reconnect the vacuum line.
- Disconnect the ASV-to-check valve hose and connect a pressure gauge to it.
- Increase the engine speed. The relief valve should open when the pressure gauge registers 2.7-6.5 psi.
- If the ASV fails any of the above tests, replace it. Reconnect all hoses.
The vacuum delay valve is located in the line which runs from the intake manifold to the vacuum surge tank. To check it, proceed as follows:
- Remove the vacuum delay valve from the vacuum line. Be sure to not which end points toward the intake manifold.
- When air is blown in from the ASV (surge tank) side, it should pass through the valve freely.
- When air is blown in from the intake manifold side, a resistance should be felt.
- Replace the valve if it fails either of the above tests.
- Install the valve in the vacuum line, being careful not to install it backward.
1983 And Later
The EACV should be checked with the engine in three stages: cold, idling warm, and running at 2000 rpm at normal operating temperature.
- Start the engine from cold and check that air is discharged from the air by-pass hose.
- Warm the engine up to between 64°F and 109°F (after about two minutes worth of running). Idle the engine, and check that air is not discharging from the by-pass hose.
- Run the engine up to 2000 rpm after the thermostat has opened fully (normal operating temperature). Check that air is being discharged intermittently (in staggered impulses) from the hose.