Exhaust Gas Recirculation (Egr) - Mityvac MI8000 Manual Del Usuario

10) The pump gauge should indicate 540-750 mbar
(16-22" Hg). Consult the vehicle's service manual
for a more accurate specification. No reading or
a low reading would indicate a leaky or plugged
vacuum line, or more serious engine problem.
11) Disconnect the vacuum pump from the vacuum
line, and plug the line temporarily. Connect the
pump to the vacuum port on the regulator.

eXhaust Gas recircuLation (eGr)

An Exhaust Gas Recirculation (EGR) sys tem is used
on most modern engines to reduce Oxides of
Nitrogen (NOx) emis sions. During the combustion
process, nitrogen, which makes up 80 percent of
the air, will mix with oxygen at tempera tures
above 2,500°F. During the combustion process,
temperatures in the cylinders go well above
3,500°F providing the ideal conditions for the
formation of NOx.
SYSTEM OPERATION
To reduce the formation of NOx, it is necessary to
lower the combustion temperature. This is most
often done by introducing exhaust gases back into
the combustion chamber through the use of an
EGR valve. The EGR valve (FIGURE 6) may be
operated by ported vacuum from above the
throttle plates, or by a sophisticated control
system that modu lates the amount of EGR
depending on the temperature of the coolant,
No Vacuum Signal
Valve closed, exhaust blocked
FIGURE 6: EGR VALVE OPERATION
Form 824357
fueL pressure reGuLator
To Vacuum Source
12) Use the pump to apply vacuum to the regula-
tor while watching the gauge on the fuel pressure
tester.
13) Fuel pressure should increase one pound for
every two inches of Hg vacuum applied to the regu-
lator. If not, replace the fuel pressure regulator.
ambient air temperature, engine speed or load.
An EGR valve that does not have a sophisticated
control system must be fully closed with a vacuum
of less than 65 mbar (2" Hg) and begin to open
with 65 to 285 mbar (2 to 8.5" Hg) of vacu um.
At idle and wide-open throttle, the ported vacuum
supply is low and the valve should be closed.
Some cars have a Back-Pressure Transducer Valve
(BPV) to modulate the operation of the EGR system.
Some cars have a Venturi Vacuum Amplifier (VVA)
to do the same job. The effect is to modulate the
amount of EGR according to the load on the engine.
To improve cold drivability, most cars are equipped
with some type of vacuum control device to shut off
EGR while the engine is cold.
EGR systems fail in two ways. Either the valve may
fail due to a fault of its own, such as a ruptured
diaphragm, or due to a loss of control vacuum.
To Vacuum Source
Vacuum Signal Applied
Valve open, exhaust admitted to intake manifold
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