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6E-2
1977 PONTIAC SERVICE MANUAL
material containing platinum and palladium.
THE CATALYTIC CONVERTER REQUIRES
THE USE OF UNLEADED FUEL ONLY.
Periodic maintenance of the exhaust system is not
required; however, if the car is raised for other service, it is
advisable to check the general condition of the underfloor
catalytic converter, pipes and mufllers.
-
Refer to Section: 6F, Exhaust System, for catalytic
converter service procedures and diagnostics.
EARLY FUEL EVAPORATION SYSTEM
(EFE)
The EFE system is used to provide a source of rapid heat
to the engine induction system during cold driveaway. Rapid
heating is desirable because it provides for quick fuel
evaporation and more uniform fuel distribution to aid cold
driveability. It also reduces the length of time carburetor
choking is required making reduction in exhaust emission
levels possible.
Two types of EFE are used on Pontiac vehicles. Some
V8 engines use an orifice EFE system which consists of an
orifice restriction in one leg of the exhaust crossover pipe. The
restriction increases the flow of exhaust gases thru the
exhaust crossover under the intake manifold. The orifice
system is in effect whenever the engine is running. The other
system uses a valve which increases the exhaust gas flow
under the intake manifold during cold engine operation. The
valve is vacuum operated and is controlled by a thermal
vacuum switch (TVS) which passes vacuum to the valve when
the coolant temperature is below the calibration value.
Diagnosis and service procedures of the EFE system are
in this section.
EXHAUST GAS RECIRCULATION
SYSTEM (EGR)
The Exhaust Gas Recirculation System is used on all
engines. It meters exhaust gas into the induction system for
recirculation through the combustion cycle to reduce oxides
of nitrogen emissions. There are two types of EGR systems;
ported and exhaust back pressure modulated. The ported
system uses a timed vacuum port in the carburetor to regulate
the amount of exhaust gas recirculation. The back pressure
modulated system regulates the timed vacuum according to
the exhaust back pressure level. The vacuum regulation is
achieved by either a separate back pressure transducer
sandwiched between the EGR valve and the manifold or by
internal EGR valve design.
The EGR valve remains closed during periods of engine
idle and deceleration to prevent rough idle from excessive
exhaust gas dilution in the idle aidfuel mixtures.
Diagnosis and service procedures of the EGR system are
in this section.
CLOSED POSITIVE CRANKCASE
VENTILATION SYSTEM (PCV)
All engines have a closed Positive Crankcase Ventilation
System to provide more complete scavenging of crankcase
vapors. See Figure 6E-2.
To maintain idle quality, a PCV valve is used which
restricts the ventilation system flow whenever intake
manifold vacuum is high. See Figure 6E-3.
Diagnosis and service procedures for the PCV system are
in this section.
CHOKE CALIBRATION
The choke is an important part of exhaust emission
control. The choke is calibrated to provide the best cold
engine performance while remaining within exhaust emission
limits. Variations in choke systems are described in Section
6C, Fuel System. Choke adjustment and service procedures
are in Section 6C.
THERMOSTATIC AIR CLEANER (TAC)
The Thermostatic Air Cleaner (TAC) is on all engines.
It uses a valve in the air cleaner inlet, controlled by either
a vacuum motor or thermostatic coil, to mix pre-heated and
non pre-heated air entering the air cleaner to maintain a
controlled air temperature into the carburetor. The vacuum
motor is modulated by a temperature sensor in the air cleaner.
The pre-heating of the air cleaner inlet air allows leaner
carburetor and choke calibrations resulting in lower emission
levels, while maintaining good driveability. Some engines use
a TAC check valve to hold the damper closed during low
temperature, low manifold vacuum operating conditions.
Diagnostics and service procedures for the thermostatic air
cleaner are in this section.
AIR INJECTION REACTION SYSTEMS
An air injection reaction system is used on some engines
to provide additional oxygen to continue the combustion
process after the exhaust gases leave the combustion
chamber. Two types of air injection reaction are used and are
identified by the type of device used to inject the air. Some
engines use an engine driven pump to provide pressurized air
which is injected into the exhaust system. Systems using an
engine driven pump, called AIR systems, may inject the air
into either the exhaust port of the cylinder head, exhaust
manifold, or the exhaust pipe. The AIR system operates at
all times and will bypass air only for a short duration of time
during deceleration and at high speeds. The diverter valve
performs the bypass function, and the check valve protects
the air pump from damage by preventing a back flow of
exhaust gas.
AIR ON V6 CALIFORNIA AND HIGH
ALTITUDE ENGINES
The AIR system used on V6 engines in 1977 uses several
new devices for regulating the injection of air into the exhaust
stream. The new components are:
1. Vacuum differential valve
2. Air bypass valve
3. Differential vacuum delay and separator valve
The purpose of the vacuum differential valve is to
prevent backfiring in the exhaust system. Throttle closure at
the beginning of a deceleration temporarily creates fuel air
mixtures which are too rich to bum. These mixtures, when
they reach the exhaust, become burnable when combined
with injection air. The next firing of the engine ignites this
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