EGR Systems

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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 higherengine 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 tocontrol 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.) toimprove 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 ishigher.

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Heres two more pictures of EGR

valve designs...

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EGRjets

The small EGR jets

meter a small amount

of exhaust gases intothe air fuel mixture.

The jets are small

enough that they do

not upset the idle air-fuel mixture.

N k

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Now you know

about EGRsystems!!!

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Brought to you by...

Hawaiian Brian Dean