Exhaust Gas Recirculation (EGR)

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Exhaust Gas Recirculation(EGR)
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What the heck does this thing do?

• Allows burned exhaust gases to enter the engine
  intake manifold.
• Reduces NOx emissions
• When exhaust gases are added to the air fuel
  mixture, they decrease peek combustion
  temperatures...
  ----For this reason, an exhaust gas recirculation
  system lowers amounts of NOx in exhaust.

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Whats in an EGR system?

• A vacuum operated EGR valve. -AND-
• A vacuum line from the carburetor

Hmmm...
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Heres what they look like...
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The EGR valve consists of...

• A vacuum diaphragm
• A spring
• A plunger
• An exhaust gas valve
• A diaphragm housing

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Whats the valve designed to do?

• Control the exhaust flow into the intake
  manifold...

SEE THE PHOTO!!!
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Basic EGR system operation...
At idle, the throttle plate in the carburetor or
fuel injection throttle body is closed. This
blocks off engine vacuum so it cant act on the
EGR valve. The EGR spring holds the valve shut
and exhaust gases do NOT enter the intake
manifold. If the EGR valve were open at
idle, it could upset the air-fuel mixture and the
engine could stall!!!
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More about EGR system operation...
When the throttle plate is swung open to
increase speed, engine vacuum is applied to the
EGR hose. Vacuum pulls the EGR diaphragm up. In
turn, the diaphragm pulls the valve open. Engine
exhaust can then enter the intake manifold and
combustion chambers. At higher engine speeds,
there is enough air flowing into the engine that
the air-fuel mixture is not upset by the open EGR
valve.
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Are all EGR systems the same?
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NO!
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Some different types of EGR systems...
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Back-pressure EGR valve

• Uses both engine vacuum and exhaust back pressure
  to control valve action.
• This provides more accurate control of EGR valve
  opening.

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Engine coolant temperature switch

• Prevents exhaust gas recirculation when the
  engine is cold. (A cold engine doesnt have
  extremely high combustion temperatures, thus, it
  doesnt produce very much NOx.)
• Blocks the vacuum to the EGR valve below 100
  degrees Fahrenheit (37.8 degrees C.) to improve
  the drivability and performance of the cold
  engine.

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Wide open throttle valve (WOT)

• Sometimes connected into the vacuum line to the
  EGR valve.
• Opens under full acceleration to provide venturi
  vacuum to the EGR valve.
• At wide open throttle, intake manifold vacuum is
  very low, but venturi vacuum is higher.

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Heres two more pictures of EGR valve designs...
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EGR jets

• The small EGR jets meter a small amount of
  exhaust gases into the air fuel mixture.
• The jets are small enough that they do not upset
  the idle air-fuel mixture.

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Now you know about EGR systems!!!
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Brought to you by...Hawaiian Brian Dean