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5/11/05 9:44am - Original Message: 'EGR valve'
Toms82
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Vette(s):
1982 Collector Edition

Joined: 3/12/2004
Posts: 67

What does an EGR valve do? How can you tell if it is not working properly?

Thanks,

Tom



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5/11/05 3:03pm - Reply: 'EGR valve'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410

EGR stands for Exhaust Gas Recirculation valve.

It allows exhaust gas through the intake passages to enter the intake manifold chamber.  This mixes some exhaust gas with the intake air fuel mixture.

Exhaust gas has been burned.  It cannot burn again.  You can't light ashes.  Nor is it oxygen or fuel.  Due to these facts, it will not affect the air fuel ratio (A/F).  But it will dilute it.  This means instead of having 100 % of what is in the cylinder fresh air and fuel, it may be 90, 80 or even 70%, with the remainder being inert gas.

This has the effect of cooling the combustion in the cylinder.  The target is to keep the cylinder combustion temp below 2500 deg F.   Above that temp, the engine will create a lot of NOx emissions ( worse for you than Carbon Monoxide ) and it creates preignition and ping.  Very bad for us and for the engine.

Cooling the mix prevents both of these.  We don't need or want EGR at idle.  There is too little air in the cylinder, and if we dilute it the car will idle poorly, if at all.  The cylinder does not make enough heat to be a problem at idle.

At part load, part throttle, the cylinder does get quite hot, and needs the cooling.  So EGR is allowed.  At full throttle adding EGR would slow the car down.  Less fresh air and fuel will result in less power.  So no EGR at or near WOT (Wide Open Throttle)   Under hard acelleration conditions, the fuel mix is richened up to create maximum power.  Rich mixtures run cooler, so the EGR is not needed. 

Lean mixtures run hotter, so an under jetted carb will create pinging.  Over jetting can foul plugs and at best, cut fuel mileage.

Anything that involves combustion will be a factor in cylinder combustion temp.  More timing will increase combustion temp, retarted timing will be cooler.  Aluminum cylinder heads can operate more timing due to the fact that heat transfer is improved, and thus the cylinder can run cooler.  There are many factors.  High octane fuel burns cooler (yes, cooler) then low octane, thus preventing ping. Cooler burning high octane burns for a longer period of time, and although cooler, creates more heat due to increased burn time.  Temp and heat are two different things.

EGR can be checked in a couple of ways.  The large EGR valves on our cars have access to the diaphram on the bottom of the large section of the valve.   First at idle, reach under it and push the diaphram up.  the car should bog, idle rough, or perhaps die.  If it does this the passages are clear.  If not the passages are clogged.

Now with still reaching under and feeling the diaphram, rev the warmed up engine.  The valve should lift up.   If it passed both of these test, all is functioning and okay.  If it bogged when you pushed up, but does not when you rev the engine, pull the vacuum line and check for vacuum when the engine is revved up.  If there is vacuum, but the valve did not respond, the valve is bad.   If there is no vacuum you have a control problem. 

Control comes from a ported vacuum on the carb.  This should not have vacuum at idle but will with part throttle.  Full throttle makes the vacuum drop to nothing.  Don't try to go full throttle. That could damage the engine with no load.   If vacuum responds properly, follow the line to a Thermo Vacumm Valve on the intake manifold.  This prevents vacuum from reaching the EGR when the engine is cold.  When warmed up, the valve opens and allows EGR.



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5/11/05 4:02pm - Reply: 'EGR valve'
Toms82
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Vette(s):
1982 Collector Edition

Joined: 3/12/2004
Posts: 67

Ken,

Thank you for that excellent explanation.

Regards,

Tom



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5/11/05 6:48pm - Reply: 'EGR valve'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410
You're welcome.

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On the "Tail of the Dragon"
(some day, no strike that, October 2008 it turned red, still in progress!)

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7/14/11 4:05pm - Reply: 'EGR valve'
dskopp
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Oak Creek, WI - USA

Vette(s):
1981 Great White Shark. Red Interior, 350/190hp. PS, PB (SS), A/C CC, T-Tops, Going to remain as Stock as possible. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vetts Car Club. 175,000 Original miles!!

Joined: 5/21/2008
Posts: 1956
Is this a great place?? or what??  Now if only we could solve world problems!!
Kudo's to the Kstyer!!!
DanClap


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7/15/11 7:40am - Reply: 'EGR valve'
crossfire1982
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Cramerton, NC - USA

Vette(s):
black 1982 coupe slate gray interior, 350 crossfire, 1985 fuel pump, Steeroids R&P conversion

Joined: 8/22/2006
Posts: 1094
Ken, thanks for the explanation of the EGR funciton.  I've never seen it explained that well. I never fully understood why it was needed.  I learn something from you guys every day.


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7/15/11 7:59am - Reply: 'EGR valve'
manchestershark Lifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Joined: 10/31/2007
Posts: 1895
Smile We really are good guys. We consider the new people with Exellent Group Relations, EGR problems.Clap  Well put Ken. THANKS

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7/15/11 12:28pm - Reply: 'EGR valve'
tb2k82ce Lifetime Member
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Lemon Grove, CA - USA

Vette(s):
1982 C3 Collectors Edition 44000 miles, sat in the sun most of it's life, My wife purchased it for me for fathers day in 2007 from her girl friend that had it for 19 years. It is on the road again. I'm retired but it is now my daily driver.

Joined: 10/17/2007
Posts: 2007
Ken that just made it into my archives.  Every time I see something like this I copy it to a word document and make a pdf of it then store it in a Corvette repair folded.


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7/15/11 12:32pm - Reply: 'EGR valve'
ebo Lifetime Member
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Holland Patent, NY - USA

Vette(s):
#1 *1980 White, Red interior 14,000 mile #2 *1980 Red, Oyster interior 93,000 miles Resto project car, rebuilt to 383 stroker

Joined: 6/3/2008
Posts: 4395
This was posted by Ken back in 2005
I put EGR valve into the search area here on this site....it's on the right of your screen down a bit.
Another great tool and easy to use.
Ken has not been on in a while so I'll send him a text to tell him we are talking about him again.
Evil Smileebo


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Evil Smileebo
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