A belt-driven air pump, mounted on the front of the engine, is used to inject air into the exhaust ports. This causes oxidation of these gases and a considerable reduction in carbon monoxide and hydrocarbons. The system consists of the pump, a check valve to protect the hoses and pump from hot gases, and a diverter-pressure relief valve assembly. Later models add a vacuum and coolant temperature controlled air switching valve to the system. The switching valve allows air flow to the exhaust ports during warmup, then diverts it to the exhaust manifold or pipe, depending on the engine.
Belt Tension and Air Leaks
- Check the pump drive belt tension. There should be about 1 / 2 in. play in the longest span of belt between pulleys.
- Turn the pump by hand. If it has seized, the belt will slip, producing 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 antibackfire valve.
- Connect a pressure gauge 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 and between 2-6 psi. If it is unsteady or falls below this, 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.Check Valve Test
- Before starting the test, check all of the hoses and connections for leaks.
- Detach the air supply hose(s) from the check valve(s).
- Insert a 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.
- Repeat Step 3 if two valves are used.
- With the engine running at normal operating temperature, gradually increase its speed to 1,500 rpm. Check for exhaust gas leakage. If there is any, 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.