The discussion of fuel economy in the EGR plate kit thread prompted a thought. The motivation of most to go into testing mode with the EGR is to eliminate gunk into the intake. Economy and performance are another potential motivation but no one seems to agree on tangible benefits. When my EGR somehow mysteriously plugged one weekend (someone must have put some sort of plate in it) I did not have enough of a baseline of fuel mileage averages to see any measurable difference.
The EGRs function is to give gasses a second opportunity to combust but is it also not designed to give FUEL VAPORS a second opportunity to combust?

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

The function of the EGR is to let exhaust gas into the air stream.........displacing oxygen.........and thereby reducing the combustion temperature. It does not give the exhaust gas "a second opportunity to combust". Ideally, there is no available fuel in the exhaust gas to enable additional combustion.

The fuel economy benefit from discontinuing the use of the EGR is minimal. Nobody has been able to document it with certainty.

1984 300d Turbo 136k
The Egr Is Ok When It Not Binding Or Sticking Open, I Remove The One
My Car To Clean It With Carbon Cleaner, Open The Valve With A
Hand Vacuum Pump It Open And Close Ok, In The Car At Fuel Stop
It Would Slow Close And Power Up It Was Ok, After 1/2 Mile Would Stick Open Again Power Loss Of The Turbo, Input Pressure Of Intake
Was A Loss Due To Open Egr Valve Sticking Open, New One Is $133.00
New Car Driving Now. Fast Diy 1/2 Hr Its On Top Right Front Of Engine 2 Bolts, One Clamp Bolt.

hey brian i think there's going to be a glut of used egrs up for sale on e-bay shortly .. lol

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

The purpose of EGR is to cool down combustion temperatures (reducing NOx) by taking area up that could have been fresh air. The exhaust gas entering the intake is inert.

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http://www.uni-stuttgart.de/impulse/...h_bosch_kl.jpg

Love the Bob!

Don't laugh. Somebody might get $50. for that valve. I think it's over $150. at the dealer.

i wouldn't be surprised!

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

As stated, the EGR vavle is there to reduce combustion temps and reduce NOx emissions. It allows ehaust fumes to mix with the intake gasses displacing some of the oxygen. If working properly on a gasser, it should allow just enough oxygen to allow complete combustion. On a diesel, it should continue to allow an excess of oxygen.

Now what hasn't been stated, how it reduces combustion temperatures. With a reduced oxygen mixture, the diesel fuel burns slower. This prevents a sharp temperature spike in one area around the injector . This allows the fuel to be burned in a more uniform manner throughout the cylinder distributing the temperature increase.

As far as power and efficiency the effects are minor but measurable. Slowly burnning fuel allows less of the piston stroke to extract power from. The EGR also heats the intake charge allowing less air mixture into the cylinder reducing power output more.

There are some ways to mitigate the effects of the EGR. Adding an intercooler to a turbocharged engine that EGR system was not designed to sense and adjust to inlet temperatures allows you to sneak in a higher oxygen content under its nose. I belive this is perfectly legal to do under federal law as you are not removing or disabling an emissions control device. Infact, the lower inlet temperatures may reduce NOx emissions more buy reducing combustion temps further.

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green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

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