DESCRIPTION
The air injection system adds a controlled amount of fresh air to the exhaust gases, at the exhaust manifold or downstream, to aid in complete oxidation of the exhaust gases. This results in reduced levels of carbon monoxide (CO) and hydrocarbon (HC) emissions.
Air pump air injection systems consist of a belt driven air pump, a switching/relief valve, hoses, and check valves to protect the hoses and other components from hot gases in the injection tubes.
PULSE AIR FEEDER
The main-reed valve responds to pressure fluctuations generated within the number 3 cylinder crankcase, since the crankcase is sealed by a seal cover. This cover has a small hole for discharging oil and any blow-by gases.
The sub-reed valve is actuated by exhaust vacuum generated from pulsation in the exhaust system between the front and rear catalytic converters.
AIR PUMP
On all engines except the 2.2L, the air pump is belt driven and is mounted at the front of the engine with power take-off from the crankshaft pulley. The air pump on the 2.2L engine is mounted at the rear of the engine and is driven by the camshaft pulley.
On 1.7L engines, intake air enters the air pump through a tube at the rear of the pump. On all other pumps, intake air enters the air pump through a centrifugal filter fan on the front of the pump.
| CAUTION | The intake tube at the rear of the pump used on 1.7L engines is larger in diameter than the discharge tube. If hoses are not connected properly, pump damage may occur. |
AIR SWITCHING VALVE
This valve directs air injection flow to either the location near the exhaust ports or to the downstream injection point. It also serves as a relief valve at high engine speeds.
A vacuum signal, from either a coolant control engine vacuum switch (CCEVS) or vacuum solenoid, causes the switching valve to open. This allows air pump air flow into the exhaust ports.
When the CCEVS shuts off vacuum to the switching valve, a bleed orifice in the vacuum line of the combination valve allows vacuum to go to zero. This causes the valve to switch air pump air to the downstream injection point.
Cutaway View of Air Switching Valve. Scheme 38
CHECK VALVE
This valve is located in the injection tube assemblies that lead to the exhaust manifolds or to the downstream injection point. The valve has a one-way diaphragm which prevents hot exhaust gases from backing up into the hoses and pump.
This valve will protect the system in the event of air pump belt failure, abnormally high exhaust system pressure or air hose rupture.
SERVICE PROCEDURES
| CAUTION | DO NOT LUBRICATE AIR PUMP. Wipe all oil off of pump housing. Oil in the pump will cause rapid deterioration and failure of internal pump components. |
Complete system should be checked at regular intervals. Engine tune-up should be checked whenever air injection system is not operating properly. Belts must be in good condition and set to proper tension.
Servicing of air pump is limited to replacement of centrifugal fan filter or the entire pump. Do not clamp pump in a vise or use a hammer on pump housing.
To replace centrifugal filter, insert needle nose pliers between filter fins and break fan from hub. Install new fan, using pulley and bolts to draw fan down evenly.
Note. Fan might have a slight squeal until sealing lip is worn in. Air injection system is not completely noiseless. Normal noise increases in pitch as engine speed increases.
| CAUTION | If the engine compartment is to be cleaned with steam or high pressure liquids, fan filter should be masked off to prevent liquid from entering air pump. |
- With engine running, apply vacuum to valve. Air should be injected upstream only.
- If air escapes from silencer ports or is applied upstream and downstream, valve is faulty and must be replaced.
- To check operation of this valve, remove air supply hose from check valve inlet tube.
- With engine operating, listen for exhaust leakage at check valve. If exhaust gases escape from valve, valve must be replaced. Also check for leaks at all other connections.