Confused on EGR

I'd say your right, but the gain/loss of fuel economy or power would be so small it probably wouldn't be worth much of anything. Besides, doesn't the ECU freak out if you just take off the EGR?

The EGR system has a vacuum source (line from the intake manifold), a computer operated electrical vacuum regulator, the EGR valve and the passages in the heads and intake manifold that route exhaust gas to the EGR valve. The computer uses RPM, Load. and some other factors to tell the vacuum regulator to pass vacuum to open the EGR valve. The EGR sensor tells the computer how far the EGR valve is open. Then computer adjusts the signal sent to the EGR vacuum regulator to hold, increase or decrease the vacuum.

The EGR shuts off at Wide Open Throttle (WOT), so it has minimal effect on performance. The addition of exhaust gas drops combustion temperature, increases gas mileage and reduces the tendency of the engine to ping.

Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.

It's about $20 from Borders.com see http://www.amazon.com/ . Select boo...very good, and I found it to be very helpful.

The addition of exhaust gas drops combustion temperature,

Click to expand...

how can adding burnt hot gasses lower combustion temps?

if the difference is so minute, whats the big deal, leave it on! lol
Paul Perreca

chobracobra said:

how can adding burnt hot gasses lower combustion temps?

Click to expand...

Because the exhaust gas is still cooler than the combustion temps. Plus it is cooled further by the coolant that flows through the EGR spacer. Lowering the coolant temps in the combustion chamber this way allows the computer to dial in more timing. Removing the EGR without a custom chip to let the computer know has resulted in pinging for some people.

i would just assume to leave it on.....but if you plan on buying a bigger TB and also some other things that require the computer to be twEECed than dont worry about the EGR. or am i wrong?

By injecting a small amount of exhaust into the manifold, a like amount of air/oxygen is displaced. This inert gas in the combustion chamber results in cooler temperatures during combustion. Because the combustion temps are cooler, the computer can add more timing advance and lean the fuel mixture out without risking detonation. If you were to hook up a wide band O2 sensor and look at a/f ratios during times when the egr is working, you'd see mixtures leaner than stoichiometric - 15, 16, 17:1. That's how fuel is saved - without having to worry about detonation as much - timing is advanced and fuel is pulled to run a leaner mixture.

That's why when egr systems fail, detonation is frequently a symptom that shows up. The computer keeps adding timing and pulling fuel, but without the inert exhaust to cool the chamber, combustion temps rise, and detonation often occurs.

that was good info michael i understand it better now.

i still dont understand how re-using exhaust gasses lowers temps and is better than sucking in, plain cool fresh air.

When you dilute the air/fuel mixture with exhaust (which is inert) -- you have less air/fuel mixture to combust. Less air fuel mixture combusting means less pressure and therefore less temperature.

Do a google on 'exhaust gas recirculation'. There are 10's of thousands of explanations. Because temps are reduced, NOx emissions are also reduced.

By the way - if you simply let more cool, fresh air in (oxygen comes as a part of it), and you put the same amount of fuel in, the mixure becomes leaner. All things equal, the leaner the mixture, the hotter it is (more NOx created; greater chance of detonation). The richer the mixture the cooler it is.

But you don't want to cool the mixture by making it richer - that wastes fuel, and creates more unburned hydrocarbons and more carbon monoxide.

EGR allows NOx be reduced, and less fuel to be used.

Here's a blurb which summarizes it by Henry Guzman:

"Exhaust gas recirculation (EGR) systems were introduced in the early '70s to reduce an exhaust emission that was not being cleaned by the other smog controls. Oxides of nitrogen (NOx) are formed when temperatures in the combustion chamber get too hot. At 2500 degrees Fahrenheit or hotter, the nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) and the presence of sunlight, produces an ugly haze in our skies known commonly as smog.

How to reduce NOx NOx formation can be reduced by:

* Enriching the air fuel (A/F) mixture to reduce combustion temperatures. However, this increases HC and carbon monoxide (CO) emissions.
* Lowering the compression ratio and retarding ignition timing; but this leads to reduced performance and fuel economy.
* Recirculating some exhaust gases.

How EGR systems work The EGR valve recirculates exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process by several hundred degrees, thus reducing NOx formation.

The design challenge The EGR system of today must precisely control the flow of recirculated exhaust. Too much flow will retard engine performance and cause a hesitation on acceleration. Too little flow will increase NOx and cause engine ping. A well-designed system will actually increase engine performance and economy. Why? As the combustion chamber temperature is reduced, engine detonation potential is also reduced. This factor enabled the software engineers to write a more aggressive timing advance curve into the spark timing program. If the EGR valve is not flowing, onboard diagnostics (OBD) systems will set a code and the power control module (PCM) will use a backup timing curve that has less advance to prevent engine ping. Less timing advance means less performance and economy. "

Does this mean that the EGR actually increases performance?

Or does it decrease performance but as a byproduct more timing can be used which gains some back (or increases even?)?

89MustangGX said:

Does this mean that the EGR actually increases performance?

Or does it decrease performance but as a byproduct more timing can be used which gains some back (or increases even?)?

Click to expand...

The EGR does not fuction at WOT, so performance is not hurt.

89MustangGX said:

Does this mean that the EGR actually increases performance?

Or does it decrease performance but as a byproduct more timing can be used which gains some back (or increases even?)?

Click to expand...

yeah, Nick is right (and Adam, i know you knew that). i would not say that it increases performance, but it sure does increase non-demand performance and economy.

I would say it increases performance in the area of emissions reduction and fuel economy (you have to define what you mean by performance), without harming peak HP generation as it only functions during light load/part throttle conditions. It's one of the few win-win emission/fuel economy gadgets. The only downside is the clutter.

HISSIN50 said:

yeah, Nick is right (and Adam, i know you knew that). i would not say that it increases performance, but it sure does increase non-demand performance and economy.

Click to expand...

Michael Yount said:

I would say it increases performance in the area of emissions reduction and fuel economy (you have to define what you mean by performance), without harming peak HP generation as it only functions during light load/part throttle conditions. It's one of the few win-win emission/fuel economy gadgets. The only downside is the clutter.

Click to expand...

I know that it does not function at WOT, so my question is, how do you run more timing with it? Or is it that you can run more timing in the curve but total timing is the same?

That's what I'm really trying to ask.

If you compare two identical cars, one with and one without EGR -- will one be faster in a race or will you only see the difference in fuel economy and emissions (and the car show!)?

Hopefully that's a better way to ask ... ?