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DESCRIPTION AND OPERATION
EGR COOLER
Using engine coolant, the EGR cooler lowers the
temperature of exhaust gas coming from the EGR
valve. The cooler contains a series of vanes that
increase cooling efficiency by swirling the hot gas
before it enters the EGR mixing chamber with air
from the charge air cooler. The swirling action
also reduces undesirable solids in the exhaust
gas.
EGR CROSSOVER (COOLER OUTLET) PIPE
The EGR crossover pipe carries the exhaust gas
from the EGR cooler to the venturi. The tube
passes in front of the cylinder block behind the
fan mounting bracket. It is connected to the
venturi on the left side of the block.
EGR VENTURI SYSTEM
The gas flows through a venturi equipped with
two differential pressure sensors. The venturi
changes the speed and density of the flow. The
sensors report the pressure difference to the
EECU.
The venturi system is calibrated as a unit. If
replacement is required, the entire assembly
along with the sensors must be replaced as a
unit.
EGR MIXER
On a conventional chassis, the piping from the
venturi returns upward to the EGR mixer at the
front of the inlet manifold above the cylinder head
(valve) cover.
On an LCF chassis, the piping from the venturi
continues rearward to the EGR mixer mounted on
top near the rear of the inlet manifold.
The EGR mixer is the meeting point for cooled,
recirculating exhaust gas and outside air from the
CAC. From here, the combined gases pass into
the inlet manifold and on to the combustion
chamber.
INLET AIR HEATER (OPTIONAL)
The inlet air heater mounts between the mixer
and the inlet manifold. The heater maintains a
constant temperature of the air inducted into the
combustion chamber. Constant air temperature
combined with constant fuel temperature
maximizes power output and fuel economy and
minimizes noxious emissions.
EGR DIAGNOSTICS
The EECU commands the EGR valve position
and monitors electric current consumed by the
EGR valve. An abnormally high reading indicates
a jammed EGR valve. The EECU verifies that its
command was sent and that the valve position
reflects the command. If the valve is jammed, or
its position doesn't change when commanded,
the EECU sets fault codes.
The temperature sensor provides information to
the EECU about the temperature of the exhaust
gases after the EGR cooler.
A degraded EGR cooler results in low efficiency.
The EECU calculates efficiency by comparing
EGR gas temperature with engine coolant and
exhaust temperatures. An EGR cooler clogged
with soot also causes a fault code to be set.
Exhaust Aftertreatment System
New, stringent standards for exhaust emission
control begin with the 2007 model year. The
Exhaust Aftertreatment System (EATS) has been
developed to act in combination with Ultra Low
Sulfur Diesel (ULSD) fuel and the EGR system to
reduce noxious emissions to meet the
requirement. This new system treats the exhaust
after it leaves the turbocharger on its way to the
atmosphere.
EXHAUST GAS RECIRCULATION
Diesel engine combustion does not burn all of the
combustible materials injected at each stroke.
The mixture of soot and ash and unburned
material, if allowed to enter the atmosphere,
creates harmful substances. Exhaust Gas
Recirculation (EGR) forces a quantity of the
exhaust gas back into the combustion chamber.
The net result is that a smaller quantity of
undesirable (noxious) ingredients reaches the
atmosphere.
Reducing the quantity of noxious compounds to
an acceptable level beginning in the year 2007
requires altering their chemical composition.
Directing the flow of exhaust gas through catalytic
and particulate filters makes this happen.
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