Chapter 6 Emissions control svstems
6-9
Reed,valve
Ai! cleaner
Air pipe
Catalytic
converter
6.1 Secondary Air Supply (SAS) system (typical)
Air hose
\
To
air
cleaner
6.5 Checking the air control valve diaphragm on 1965 and later
SAS systems
the piston moves aown. At small throttle openings, there is a large pres-
sure difference, giving the jet air a high velocity. This scavenges the resid-
ual gases around the spark plug and creates good ignition conditions. It
also produces a strong swirl in the combustion chamber, which lasts
throughout the compression stroke and improves flame propagation after
ignition, assuring high combustion efficiency and lowering exhaust emis-
sions. As the throttle opening is increased, less jet air is forced in and jet
swirl diminishes but the increased flow through the intake valve ensures
satisfactory combustion.
3 incorrect valve clearances affect emission levels and can cause en-
gine troubles. Refer to the valve clearance adjustment Section in Chap-
ter 1 for the jet valve adjustment procedure.
4 Jetvalve removal, inspection and installation procedures are covered
in detail in Chapter 2, Part D.
5 Catalytic converter
1 Thecatalyticconverterprovides for the oxidizing of hydrocarbons and
carbon monoxide in the exhaust system, which reduces the levels of these
pollutants in the exhaust.
2 Its ceramic monolithic element, coated with a catalytic agent, is
pressed into the exhaust manifold on early models. On later models it is a
replaceable component located under the vehicle in the exhaust system.
3 The catalytic converter requires the use of the unleaded fuel only,
Leaded gasoline will destroy the effectiveness of the catalyst as an emis-
sion control device.
6.4 ’ To check the operation of the SAS reed valve, place your
finger over the valve inlet with the engine running
4 Under normal operating conditions, the catalytic converterwill not re-
quire maintenance. However, it is important to keep the engine properly
tuned. If the engine is not properly tuned, engine misfiring maycauseover-
heating of the catalyst, which may damage the converter or other vehicle
components. Heat damage can also occur during diagnostic testing if
spark plug wires are removed and the engine is allowed to idle for a pro-
longed period of time.
5 Caution:
Vehicle operation, including idling, should be avoidedifen-
gine misfiring occurs. Under these conditions the exhaust system will op-
erate at an abnormally high temperature and may cause damage to the
catalystorotherunderbodypark of the vehicle. Alteration or deterioration
of the ignition or fuelsystems, or any type of operating condition Which re-
sults in engine misfiring, must be corrected to avoid overheating the cata-
lytic converter.
6 Secondary Air Supply (SAS) system (carbureted
models only)
Description
Refer to illustration 6.1
1
The SAS system (see illustration) consists of reed valves and air
pipes that supply secondary air into the exhaust manifold and exhaust
pipe (at a point beyond the catalytic converter) for the purpose of promot-
ing oxidation (or complete burning) of any remaining unburned fuel. The
system used on 1985 and later models is somewhat more complex; it uti-
lizes a secondary air control valve and a computer-controlled solenoid
valve to control the flow of air through the reed valve and into the exhaust
manifold.
2 The SAS is actuated by exhaust vacuum generated from pulsations
in the exhaust manifold. Air is drawn through the air cleaner and directed
into the manifold by the valve motion corresponding to the exhaust pulses.
Check
Refer to illustrations 6.4,and 6.5
3 Checkthe air hose and air pipe for damage and cracks. Check the air
pipe connections for leakage.
4 Start and run the engine at idle. Disconnect the rubber air hose from
the reed valve and place your hand over the intake port of the valve (see
illustration). if suction is felt, the reed valve is operating properly. If no
suction is felt, or if pressure is felt, replace the reed valve with a new one.
5 To check the air control valve diaphragm on 1985 and later models,
hook up a hand-operated vacuum pump to the valve fitting with a short
section of hose and apply avacuum of approximately 20 in-Hg (see iiius-
tration). The pump gauge needle should remain stable.
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