See Figures 1 through 6
All of the gasoline engines used in Jeep vehicles, except the 6-226 and 8-350, have, at one time or another, incorporated the air injection system for controlling the emission of exhaust gases into the atmosphere. Since this type of emission control system is common to most of the engines, it will be explained here.
The exhaust emission air injection system consists of a belt driven air pump which directs compressed air through connecting hoses to a steel distribution manifold into stainless steel injection tubes in the exhaust port adjacent to each exhaust valve. The air, with its normal oxygen content, reacts with the hot, but incompletely burned exhaust gases and permits further combustion in the exhaust port or manifold.
The air injection pump is a positive displacement vane type which is permanently lubricated and requires little periodic maintenance. The only serviceable parts on the air pump are the filter, exhaust tube and relief valve. The relief valve relieves the air flow when the pump pressure reaches a preset level. This occurs at high engine rpm. This serves to prevent damage to the pump and to limit maximum exhaust manifold temperatures.
Pump Air Filter
The air filter attached to the pump is a replaceable element type. The filter should be replaced every 12,000 miles under normal conditions and sooner under off-road use. Some models draw their air supply through the carburetor air filter.
Air Delivery Manifold
The air delivery manifold distributes the air from the pump to each of the air delivery tubes in a uniform manner. A check valve is integral with the air delivery manifold. Its function is to prevent the reverse flow of exhaust gases to the pump should the pump fail. This reverse flow would damage the air pump and connecting hose.
Air Injection Tubes
The air injection tubes are inserted into the exhaust ports. The tubes project into the exhaust ports directing air into the vicinity of the exhaust valve.
The anti-backfire diverter valve prevents engine backfire by briefly interrupting the air being injected into the exhaust manifold during periods of deceleration or rapid throttle closure. On the 4-134 and all of the 1971 and later American Motors engines, the valve opens when a sudden increase in manifold vacuum overcomes the diaphragm spring tension. With the valve in the open position, the air flow from the air pump is directed to the atmosphere.
On the 6-225, 1966-70 6-232 and 8-327, the anti-backfire valve is what is commonly called a gulp valve. During rapid deceleration the valve is opened by the sudden high vacuum condition in the intake manifold and gulps air into the intake manifold.
Both of these valves prevent backfiring in the exhaust manifold. Both valves also prevent an over right fuel mixture from being burned in the exhaust manifold, which would cause backfiring and possible damage to the engine.