142 EMISSION CONTROLS AND FUEL SYSTEM
On 1982 and later models, the EGR valve
vacuum is controlled by the ECM of the
computer emissions system.
EGR
VALVE REMOVAL AND
INSTALLATION
1. Detach the vacuum lines from the EGR
valve.
2. Unfasten the two bolts or bolt and clamp
which attach the valve to the manifold. With
draw the valve.
3. Installation is the reverse of removal.
Always use a new gasket between the valve
and the manifold. On dual diaphragm valves,
attach carburetor vacuum line to tube at top
of valve, manifold vacuum line to tube at cen
ter of valve.
TO AIR CM
VERIER
VALVE
EGR valve and solenoid used with most computer
emissions systems—1982 shown (© Chevrolet
Motor Division)
TVS
SWITCH REMOVAL AND
INSTALLATION
1. Drain the radiator.
1. Disconnect the vacuum lines from the
switch, noting their locations. Remove the
switch.
1. Apply sealer to the threaded portion of
the new switch, and install it, torquine to 15
ft Ibs.
1. Rotate the head of the switch to a posi
tion that will permit easy hookup of vacuum
hoses. Attach the vacuum hoses to the proper
connectors.
Early Fuel Evaporation (EFE)
The 1975-81 EFE system is used to reduce
engine warm-up time, improve driveability,
and reduce emissions. The system consists of
a vacuum controlled heat valve assembly
(EFE valve) and a thermostatic vacuum switch
(TVS) installed in the coolant thermostat
housing of the engine.
The TVS controls the action of the EFE
valve. One port of the TVS is connected to a
manifold vacuum source; the other port to the
EFE valve. When the engine is cold (as
sensed by the TVS), the passage within the
TVS is open to allow vacuum to act upon the
EFE valve. The EFE valve closes, which
blocks the exhaust flow from the right side
cylinder bank. Because of the blockage, the
exhaust gas is forced through passages in the
right side cylinder head and the intake man-
ifold. The heat from the exhaust warms the
carburetor which improves the vaporization
characteristics of the fuel. The exhaust gas
exits through the left side exhaust pipe until
the EFE valve closes. As the coolant temper-
ature increases, the TVS shuts off the vac-
uum to the EFE valve. The valve then opens,
allowing the exhaust gas to follow its normal
route through the right side exhaust pipe.
1982 and later models do not use the EFE
system, due to the superior fuel handling ca-
pabilities of the Throttle Body (fuel) Injection
system.
Typical EFE valve and related components
TESTING THE EFE SYSTEM
After the vehicle has sat overnight, open the
hood and note the position of the EFE valve
control rod. Start the engine and check that
SOLENOID
VACUUM
SUPPLY
EGR VALVE
