See Figures 1 and 2
The thermactor (air injection) exhaust emission control system reduces the hydrocarbon and carbon monoxide content of the exhaust gases. This is accomplished by continuing the combustion of unburned gases after they leave the combustion chamber, by injecting fresh air into the hot exhaust stream leaving the exhaust ports or into the catalyst. At this point, the fresh air mixes with hot exhaust gases. This promotes further oxidation of both the hydrocarbons and carbon monoxide, reducing their concentration and converting some of them into harmless carbon dioxide and water.
During some modes of operation (highway cruise/wide open throttle), the thermactor air is dumped to atmosphere to prevent overheating in the exhaust system.
The following components are typical of an air injection system:
There are two types of air bypass valves: normally closed valves and normally opened valves. Both types are available in remote (inline) versions or pump mounted (installed directly on the air pump) versions. Normally closed valves supply air to the exhaust system during medium and high vacuum signals during normal engine operating modes and short idles with some accelerations. With low or no vacuum applied, the pumped air is dumped through the silencer ports of the valve. Normally open air bypass valves are available with or without vacuum vents. Normally open valves using a vacuum vent provide a timed air dump during decelerations and also dump when a vacuum pressure difference is maintained between the signal port and the vent port. The signal port must have 3 in. Hg (10 kPa) or more vacuum than the vent port to hold the dump. This mode is required in order to protect the catalyst from overheating. Normally open air bypass valves without a vacuum vent provide a timed dump of air for 1.0 or 2.8 seconds when a sudden high vacuum of about 20 in. Hg (67.5 kPa) is applied to the signal port. This prevents backfire during deceleration.Air Check Valve/Pulse Air Valve
The air check valve is a one-way valve that allows the thermactor air to pass into the exhaust system while preventing exhaust gases from passing in the opposite direction. The pulse air valve replaces the air pump in some thermactor systems. It draws air into the exhaust system on vacuum exhaust pulses and blocks the backflow of high pressure exhaust pulses. The fresh air completes the oxidation of exhaust gas components.Anti-Backfire (Gulp) Valve
The anti-backfire (gulp) valve is located downstream from the air bypass valve. Its function is to divert a portion of the thermactor air to the intake manifold when it is triggered by intake manifold vacuum signals on deceleration. This helps prevent an overly rich mixture from entering the catalytic converter.Air Supply Pump
This pump is only utilized by air injection systems, not pulse air systems.
The air supply is a belt driven, positive engagement vane-type pump, that supplies air for the thermactor system. The pump is available in two sizes: 11 cubic inch (180cc) and 19 cubic inch (311cc), depending on the particular vehicle application. The 11 cubic inch pump receives air through a remote filter that is attached to the air inlet nipple or through an impeller-type centrifugal air filter fan. The 19 cubic inch pump uses an impeller-type centrifugal air filter fan which separates dirt, dust and other contaminants from the intake air, using centrifugal force. The air supply pump does not have a built in pressure relief valve, but the system does use a bypass valve.
TestingAnti-Backfire (Gulp) Valve
- Disconnect the air supply hose from the air pump side of the anti-backfire valve.
- Look inside the valve through the disconnect port and observe the valve pintle.
- Accelerate the engine to about 3000 rpm. Release the throttle, the pintle should open and then close.
- If it does not perform as indicated, replace the defective valve.
- Check the belt tension. If not within specification, adjust it properly.
- Disconnect the air supply hose from the bypass control valve.
- If the air flow is felt at the pump outlet and flow increases, as the engine speed increases, the pump is functioning properly.
- If the pump does not perform properly, replace as required.
- Disconnect the air supply at the pump side of the valve.
- Blow through the check valve, toward the manifold, then attempt to suck back through the valve. Air should pass in the direction of the exhaust manifold only. Replace the valve if air flows both ways.
REMOVAL & INSTALLATION
Air Supply Pump
- Loosen the pivot mounting and adjustment bolt. Relax the drive belt tension and remove the belt. Disconnect the air hoses.
- Remove the adjuster and pivot nuts and bolts. Remove the air pump.
- Installation is in the reverse order of removal. Adjust the belt to its proper tension (refer to Routine Maintenance under Belts.