See Figures 1, 2 and 3
The Thermactor® emission control system makes use of a belt driven air pump to inject fresh air into the hot exhaust stream through the engine exhaust ports. The result is the extending burning of those fumes which were not completely ignited in the combustion chamber, and the subsequent reduction of some of the hydrocarbon and carbon monoxide content of the exhaust emissions into harmless carbon dioxide and water.
The Thermactor® system is composed of the following components:
Air for the Thermactor® system is cleaned by means of a centrifugal filter fan mounted on the air pump driveshaft. The air filter does not require a replaceable element.
To prevent excessive pressure, the air pump is equipped with a pressure relief valve which uses a replaceable plastic plug to control the pressure setting.
The Thermactor® air pump has sealed bearings which are lubricated for the life of the unit, and preset rotor vane and bearing clearances, which do not require an periodic adjustments.
The air supply from the pump is controlled by the air bypass valve, sometimes called a dump valve. During deceleration, the air bypass valve opens, momentarily diverting the air supply through a silencer and into the atmosphere, thus preventing backfires within the exhaust system.
A check valve is incorporated in the air inlet side of the air manifolds. Its purpose is to prevent exhaust gases from backing up into the Thermactor® system. This valve is especially important in the event of drive belt failure, and during deceleration, when the air bypass valve is dumping the air supply.
The air manifolds and air supply tubes channel the air from the Thermactor® air pump into the exhaust ports of each cylinder, thus completing the cycle of the Thermactor® system.
Before performing an extensive diagnosis of the emission control systems, verify that all specifications on the Vehicle Emissions Control Information (VECI) label are met, because the following systems or components may cause symptoms that appear to be emission related.
Belt Tension and Air Leaks
- Before proceeding with the tests, check the pump drive belt tension to see if it is within specifications
- 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 areas in question, is a good method of detecting leaks.
Air Output Test
- Disconnect the air supply hose at the anti-backfire valve.
- Connect a pressure 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 2-6 psi (13-41 kPa). If it is unsteady or falls below this, the pump is defective and must be replaced.
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; however, if this sound becomes louder than the road noise 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 the to be replaced as an assembly.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.
- 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.
- If two valves are used, repeat step 3 on the remaining valve.
- With the engine running at normal operating temperature, gradually increase it 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.Air Bypass Valve Test
- 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 bypass valve hose connection.
- Speed the engine up, so that it is running at 1500-300 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 of if it fails to stop flowing from the hose connection, check the vacuum lines and connections. If these are tighten, 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.
REMOVAL & INSTALLATION
See Figure 4
- Disconnect the air outlet hose at the air pump.
- Loosen the pump belt tension adjuster.
- Disengage the drive belt.
- Remove the mounting bolt and air pump.
- Position the air pump on the mounting bracket and install the mounting bolts.
- Place drive belt in pulleys and attach the adjusting arm to the air pump.
- Tighten the mounting bolts and adjust the drive belt tension. Use a suitable belt tension gauge to check the tension.
- Connect the air outlet hose to the air pump.
Air Pump Filter Fan
See Figure 5
- Loosen the air pump adjusting arm bolt and mounting bracket bolt to relieve drive belt tension.
- Remove drive pulley attaching bolts and pull the drive pulley off the air pump shaft.
- Pry the outer disc loose; then, pull off the centrifugal filter fan with slip-joint pliers.
Do not attempt to remove the metal drive hub!
- Install a new filter fan by drawing it into position, using the pulley and bolts as an installer. Draw the fan evenly by alternately tightening the bolts, making certain that the outer edge of the fan slips into the housing.
A slight interference with the housing bore is normal. After a new fan is installed, it may squeal upon initial operation, until its outer diameter sealing lip has worn in, which may require 3-30 miles (32-48 km) of operation.Check Valve
See Figures 6, 7, 8 and 9
- Apply a light coat of penetrating oil to the fitting prior to removal.
- Disconnect the air supply hose at the valve. Use a crowfoot wrench or other suitable tool.
The valve has a standard, right hand pipe thread.
- Clean the threads on the air manifold adaptor or air supply tube with a wire brush. Do not blow compressed air through the check valve in either direction.
- Install the check valve and tighten.
- Connect the air supply hose.
- Disconnect the air and vacuum hoses at the air bypass valve body.
- Position the air bypass valve, and connect the respective hoses.