Sable V6-232 3.8L (1988)
EGR Valve: Description and Operation
In this system the exhaust gases are metered through the EGR valve to a passage in the carburetor spacer thereby diluting the air fuel mixture entering
the combustion chambers. Dilution of the incoming mixture lowers peak flame temperatures during combustion and thus limits the formation of nitrogen
oxides (NOx).
Fig. 39 EGR connections. 4 & 6 cyl. engines
On four and six cylinder engines, the EGR system is basically the same as the Spacer Entry EGR System except that exhaust gas is routed directly
from the exhaust manifold, Fig. 39.
Two variables control the operation of the EGR system, 1) engine coolant temperature and 2) carburetor vacuum. When engine coolant temperature is
below the specified level the EGR system is locked out by a temperature controlled vacuum switch. The vacuum switch is installed in series with the
EGR valve. This valve receives vacuum from a port in the carburetor body. When the valve is closed due to lower coolant temperature, no vacuum is
applied to the EGR valve and no exhaust gas is fed to the air-fuel mixture. When the engine coolant temperature reaches the specified level, the valve
opens allowing vacuum to be applied to the EGR valve. Exhaust gas is then fed to the air-fuel mixture.
The second factor controlling EGR operation is carburetor vacuum. The location of the EGR port in the carburetor determines at what point vacuum is
sent to the EGR valve. Vacuum should be fed to the EGR vacuum control valve when the primary throttle plate reaches a position corresponding to a
road speed of approximately 20 mph under light acceleration.
