When the EGR VALVE is
clogged or malfunctioning, it can cause irregularities in engine
performance such as rough idling or
valve
knock, indicating that the
EGR
valve should be
inspected.
The
EGR valve works by routing a
small amount of exhaust back into the combustion chamber. When the
temperature in the combustion chamber is too high, nitrogen oxides
are produced, which combine with elements in the atmosphere to form smog. Introducing a
small amount of exhaust into the system reduces the temperature in the
combustion chamber, reducing the amount of nitrogen oxides produced.
Many
EGR valves are
mechanical, and simply have a small
valve
which opens to allow exhaust into the combustion chamber and closes
when it is not necessary, and to keep the air mixture optimal for
combustion. Some mechanical versions will not open until there is
sufficient back pressure, ensuring that the
valve
will not be open when the engine is idle or warming up and needs a
higher concentration of oxigen for
combustion. Electronic
EGR
valves are also available, and use electronics to regulate the
valve.
If the
EGR valve is stuck open, it
will essentially cause a vacuum leak, leading to inefficient
combustion, rough idling, hesitation, and sometimes stalling in extreme
cases. This is because the car cannot combust on carbon dioxide
from the tailpipe — it needs atmospheric oxygen. If the combustion
chamber is flooded with exhaust from an open
EGR
valve, it will not
function properly. To
check
and see if the
EGR valve is stuck open,
have someone idle a parked vehicle with the brake on while you examine
the plunger shaft to see if it is stuck open.
If the
EGR valve is stuck closed, emissions of
nitrogen oxides will rise, and the car may start to knock. Spark knock
happens when the fuel mixture in the combustion chamber ignites before
it has been reached by the explosion in the cylinder, resulting in a
disruption of the engine timing. In this instance, the engine should be
warmed up and revved to see if the
EGR
valve will move.
In both cases, simple repairs are possible. The
EGR valve can be clogged,
and a simple cleaning of a mechanical
EGR
valve may solve the
problem. In the case of an electrically controlled
EGR valve or a more complex
mechanical problem, replacement of the
valve
may be needed. The
EGR
valve is an expensive
motor vehicle component, and care should be taken to ensure that it
needs to be replaced rather than repaired. A reputable mechanic should
advise you appropriately.
Failure to repair or replace the
EGR
valve will not lead to a
life threatening condition, although it will reduce the life of your
car and increase the potential emissions. Especially in areas which
require smog testing, an automobile with a malfunctioning
EGR valve may not pass
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