See Figures 1 through 10OPERATION
The air injection 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 extended 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 air injection system is composed of the following components:
Air for the air injection 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 air injection 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 any 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 during sudden deceleration.
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 air injection 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 air injection air pump into the exhaust ports of each cylinder, thus completing the cycle of the air injection system.Orifice Spark Advance Control (OSAC)
See Figures 11, 12, 13 and 14
The OSAC system is used on light duty trucks to aid in control of nitrous oxide (NOx) emissions. The system controls the vacuum signal to the distributor vacuum advance unit.
A tiny orifice is incorporated in the OSAC valve which delays the change in ported vacuum to the distributor by 17 to 27 seconds, depending on the engine and truck model, when going from idle to part throttle.
When going from part throttle to idle, the change in ported vacuum is instantaneous.Catalytic Converters
The catalytic converter, mounted in the truck's exhaust system, is a muffler-shaped device containing a ceramic honeycomb-shaped material that is coated with alumina and impregnated with catalytically active precious metals such as platinum, palladium and rhodium.
The catalyst's job is to reduce air pollutants by oxidizing hydrocarbons (HC) and carbon monoxide (CO). Catalysts containing palladium and rhodium also oxidize nitrous oxides (NOx).
On some trucks, the catalyst is also fed by the secondary air system, via a small supply tube in the side of the catalyst.
No maintenance is possible on the converter, other than keeping the heat shield clear of flammable debris, such as leaves and twigs.
Other than external damage, the only significant damage possible to a converter is through the use of leaded gasoline, or by way of a too rich fuel/air mixture. Both of these problems will ruin the converter through contamination of the catalyst and will eventually plug the converter, causing loss of power and engine performance.
When this occurs, the catalyst must be replaced. For catalyst replacement, see the Exhaust System portion of Engine & Engine Overhaul .
- Check and, if necessary, adjust the belt tension. Press at the mid-point of the belt's longest straight run. You should be able to depress the belt about 1 / 2 in. (13mm) maximum.
- Run the engine to normal operating temperature and let it idle.
- Disconnect the air supply hose from the bypass control valve. If the pump is operating properly, airflow should be felt at the pump outlet. The flow should increase as you increase the engine speed. The pump is not serviceable and should be replaced if it is not functioning properly.
REMOVAL & INSTALLATION
Air Bypass Valve
See Figure 15
- Disconnect the air and vacuum hoses at the air bypass valve body.
- Position the air bypass valve and connect the respective hoses.
See Figures 16, 17 and 18
This system utilizes exhaust pressure pulsation to draw clean air from inside the air cleaner into the exhaust system. The system's function is to reduce hydrocarbon (HC) emissions.
- Disconnect the air supply hose at the check valve, position the hose out of the way and remove the valve.
- Disconnect the air hose from the aspirator valve inlet.
- Unscrew the valve from the tube assembly; you will need a hexagonal wrench at the threaded joint.
- Remove the screws securing the aspirator tube to the exhaust manifold and engine.
- Remove the aspirator tube assembly from the engine; also remove any gasket material from the exhaust manifold and aspirator tube flange.
- Install a new gasket on the exhaust manifold flange and position the aspirator tube assembly to the valve.
- Attach the aspirator valve to the tube assembly using a hexagonal wrench. Tighten to 25 ft. lbs. (34 Nm).
- Fasten the tube flange's mounting screw to 150 inch lbs. (17 Nm).
Tighten the aspirator tube bracket hold-down screws to the following torque specifications:
6-225 engine: 40 ft. lbs. (54 Nm)
- Connect the air hose to the aspirator valve inlet and air cleaner nipple.
- Disconnect the air supply hose at the valve. Use a 1 1 / 4 in. crow's foot wrench. The valve has a standard, right-hand pipe thread.
- Clean the threads on the air manifold adapter (air supply tube on the V8 engines) 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 supply hose at the check valve and position the hose out of the way.
- Remove the check valve.
- Remove the air supply tube bolt and seal washer.
- Carefully remove the air supply tube and seal washer from the cylinder head. Inspect the air supply tube for evidence of leaking threads or seal surfaces. Examine the attaching bolt head, seal washers, and supply tube surface for leaks. Inspect the attaching bolt and cylinder head threads for damage. Clean the air supply tube, seal washers, and bolt with kerosene. Do not dry the parts with compressed air.
- Install the seal washer and air supply tube on the cylinder head. Be sure that it is positioned in the same manner as before removal.
- Install the seal washer and mounting bolt. Tighten the bolt.
- Install the check valve and tighten it.
- Connect the air supply hose to the check valve.
Normally, air nozzles should be replaced during cylinder head reconditioning. A nozzle may be replaced, however, without removing the cylinder head, by removing the air manifold and using a hooked tool.
Clean the nozzle with kerosene and a stiff brush. Inspect the air nozzles for eroded tips.Air Pump Filter Fan
- Loosen the air pump attaching bolts.
- Remove the drive pulley attaching bolts and pull the pulley off the air pump shaft.
- Pry the outer disc loose, then remove the centrifugal filter fan. Care must be used to prevent foreign matter from entering the air intake hole, especially if the fan breaks during removal. Do not attempt to remove the metal drive hub.
- Install the new filter fan by drawing it into position with the pulley bolts. Make sure the fan slips into the housing. Do not attempt to install the fan by hammering or pressing it on. After the fan is installed, it may squeal for a short while until the sealing lip is fully seated (approximately 20-30 miles or 32-48 km of driving).
Some 1967 air pumps have air filters with replaceable, non-cleanable elements.Air Pump
See Figure 19
- 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 bolt.
- Place the drive belt in the pulley and attach the adjusting arm to the air pump.
- Adjust the drive belt tension, then tighten the adjusting arm and mounting bolts.
- Connect the air outlet hose to the air pump.
See Figure 20
Do not disassemble the air pump on the truck to replace the relief valve; first remove the pump from the engine.
- Disconnect the relief valve air hose.
- Unfasten the two mounting screws and release the valve.
- Remove the gasket from the mounting surface and the valve, then discard it.
- Position a new gasket on the mounting surface, making sure the holes line up.
- Position the relief valve on the mounting surface and secure with the screws. Tighten them to 125 inch lbs. (14 Nm).
- Install the air and vacuum hoses to the switch relief valve.
- Compress the locking tabs inward (together) and remove the plastic pressure setting plug.
- Before installing the new plug, be sure that the plug is the correct one. The plugs are color coded.
- Insert the plug in the relief valve hole and push in until it snaps into place.