# EGR. How does it work



## davidmayernik (Sep 19, 2005)

from what i know, EGR stands for Exhaust Gas Recirculation. after sort of eyeballing the system, it dumps whatever into the intake, after the filter. given the name, i would guess that whatever it dumps is exhaust. can anyone explain to me why that is:

a) a good thing
b) good for emissions
c) good for performance

i figure spent air screwing around the intake is bad, and would help the engine breath better, and cleaner, if i just ixnayed that whole system, freed up some underhood space, and allowed me to make my own true cool-air system that doesnt rely on the stock airbox. i really want to draw air from the hood, as it would be the easiest method, basically a custom airbox, a cone filter, and a louver, but since i'd rather not move the battery, i instead have to locate a pipe to the front bumper to draw air from the bumper.

at the very least, can anyone give me a reason to not remove the egr system and weld that hole shut? would it improve performance by a meaningful margin? please advise...


----------



## lfd75 (Nov 27, 2004)

From the dictionary of automotive terms...

(EGR) An emission control system where some of the exhaust gases are rerouted from the exhaust manifold into the combustion chamber to make sure that all fuel is burned before entering the atmosphere. The process lowers the combustion temperature and reduces the formation of oxides of nitrogen (NOx) in the exhaust.


----------



## thecolonelcm (Mar 28, 2005)

Not sure what your emissions laws are in OR, but if you remove the EGR, you probably wont pass for a variety of reasons. Lots of people get rid of it and find the right shop :wink: ... but thats your call.


----------



## Twiz (Aug 24, 2004)

How are you going to trick the ECU you still have the EGR system and get it to clear the CELs ?


----------



## pimpride (Mar 28, 2005)

Reroute past the EGR transducer.


----------



## Hydrolock (Feb 18, 2005)

It brings down combustion chamber temp, and reduces NOx. Unless your running an engine where you need all the heat you can get (race motor) your car will probably spark knock.


----------



## bigern45 (Oct 25, 2005)

*egr*

exhaust gas is inert. it has already been ignited, so it wont ignite again. when temps in the combustion chamber get extremely hot, there is pre-detenation, the mixture of fuel and air ignites because it is so hot, and you have a misfire and hear a pinging noise or spark knock. the egr valve is commanded on, and when the inert exhaust gas is allowed into the mixture, and even though it is exhaust gas, it cools the combustion chamber because it takes away from combustion. and then it reduces nox, an ozone harmful gas which is made from the cylinder temps getting over 2500 degrees.


----------



## Petrovich (May 13, 2005)

M, just a quick thought, doesn't water injection do EXACTLY what EGR does?...


----------



## bahearn (Jul 15, 2002)

EGR is used strictly to lower NOx generation. It has nothing to do with controlling detonation or "spark knock". It may influence the conditions that cause detonation but it isn't used for detonation control.

Oxides of nitrogen (NOx) are formed in any combustion event since air is 70% nitrogen. Formation rate is directly proprotional to combustion temperature. Exhaust gas, which has most of its oxygen already consumed and is therefore "inert", is routed back into the intake to lower overall oxygen concentration in the intake via dilution.

High load situations tend to make the most NOx in an engine. Idle is actually kind of tricky to keep smooth, so EPA allows EGR to be shut off. Full throttle assumes a need for 100% power production, so again EPA allows EGR to shut off. Therefore, EGR is programmed to operate only at part throttle.

If you're having idle difficulties, one of the culprits to check is EGR function. 

Race cars can remove EGR for two reasons:
1) they operate either at full throttle or no throttle. EGR wouldn't function at all and would be dead weight.
2) race cars are not licensed for street use. EPA has been kept from applying automobile pollution laws to any vehicle that does not operate on public land, i.e. open roads.

Water indeed lowers combustion temps like EGR, but exhaust gas is free and self-contained. For water injection, you need to have a tank and keep it filled. I'll assume that cost of EGR valves and control would cost the same as water pump and control.


----------



## Hydrolock (Feb 18, 2005)

bahearn said:


> EGR is used strictly to lower NOx generation. It has nothing to do with controlling detonation or "spark knock". It may influence the conditions that cause detonation but it isn't used for detonation control.


Spark knock is directly related to CC temps, therefore although EGR intended use is not to control spark knock it does have a direct relation to it, as well as other things such as octane rating/timing,cooling etc.


----------



## bahearn (Jul 15, 2002)

That's what I said when I wrote:
"It may influence the conditions that cause detonation but it isn't used for detonation control."

Detonation control for the ECU is timing. Nothing else. The ECU doesn't alter EGR flow in conjunction with the knock sensor or ignition timing. I'm being precise as to what EGR is.


----------



## Hydrolock (Feb 18, 2005)

bahearn said:


> That's what I said when I wrote:
> "It may influence the conditions that cause detonation but it isn't used for detonation control."
> 
> Detonation control for the ECU is timing. Nothing else. The ECU doesn't alter EGR flow in conjunction with the knock sensor or ignition timing. I'm being precise as to what EGR is.


An inoperative EGR valve would be a prime suspect of detonation (along with others) though.


----------



## bigern45 (Oct 25, 2005)

*who said that?*



bahearn said:


> EGR is used strictly to lower NOx generation. It has nothing to do with controlling detonation or "spark knock". It may influence the conditions that cause detonation but it isn't used for detonation control.
> 
> Oxides of nitrogen (NOx) are formed in any combustion event since air is 70% nitrogen. Formation rate is directly proprotional to combustion temperature. Exhaust gas, which has most of its oxygen already consumed and is therefore "inert", is routed back into the intake to lower overall oxygen concentration in the intake via dilution.
> 
> ...


who said that egr was used to control detonation? the "knock" sensor will more than likely let the computer know when there is some sort of detonation that is not normal. but the egr helps aid in cooling the combustion chamber therefore lower harmful emissions and no detonation due to too hot cylinders. and the only way the egr valve would effect idle control would be if it was stuck open and was constantly letting exhaust gas into the mixture. he wanted to know what the egr does, it was an a, b and c question. too much nox does not effect how your engine performs, but to get nox the conditions that are present will cause drivability problems.


----------



## Kgizzle1 (Oct 14, 2005)

your car will still pass emissions if you dont have an egr, unless it is right on the borderline of failing before you take it out. you may fail if they notice that your egr has been removed though. egr serves almost no purpose except in to reduce nox. take it out.... an 18 wheeler releases more smog in one gear shift then your sentra will in its entire life.


taking it out will not improve performance
taking it out will only slightly effect emissions

btw where is the egr valve located on my GA16.


----------



## Hydrolock (Feb 18, 2005)

Kgizzle1 said:


> your car will still pass emissions if you dont have an egr, unless it is right on the borderline of failing before you take it out. you may fail if they notice that your egr has been removed though. egr serves almost no purpose except in to reduce nox. take it out.... an 18 wheeler releases more smog in one gear shift then your sentra will in its entire life.


Depending on where you live your car could fail emissions because of NOx, and if you live in one of those areas your car WILL fail for NOX with no EGR valve. Whens the last time you saw an 18 wheeler at the inspection station? Where the hell is your reasoning?

If you take the EGR out your car WILL spark knock. And your car will make 0 NOx with a hole in the piston.


----------



## PSr_SEX-R (Feb 1, 2005)

Hydrolock said:


> If you take the EGR out your car WILL spark knock. And your car will make 0 NOx with a hole in the piston.



really?? hasn't happened to my car yet. (the hole in pistion part) i would have to disagree with that. on a side note its not worth removing the egr cuz it dosent help performance. dont waste your time hacking up your car.


----------



## davidmayernik (Sep 19, 2005)

thanks guys, this has really helped!


----------



## bahearn (Jul 15, 2002)

> If you take the EGR out your car WILL spark knock.


 :bs: 

That is SO untrue.


----------



## bigern45 (Oct 25, 2005)

bahearn said:


> :bs:
> 
> That is SO untrue.


right. i drove for years with clogged egr passages in my altima and never had any drivability problems. your car would have to be running really hot (cc temps) real long time, especially to put a hole in your piston. but you will fail emissions, especially if your vehicle is obdII compliant. it will fail the quick test, and its always best to get your vehicle in normal operating temps for the gas analysis, by then you could have nox showing up. leave the valve on, i dont know why you would want it off, unless it is stuck open.


----------



## Harris (Nov 11, 2002)

bahearn said:


> :bs:
> 
> That is SO untrue.



I agree.


Bruce, remember you and I had that argument about the EGR? Maybe I should post that link here and add fuel to that old fire.


----------



## Kgizzle1 (Oct 14, 2005)

Hydrolock said:


> Depending on where you live your car could fail emissions because of NOx, and if you live in one of those areas your car WILL fail for NOX with no EGR valve. Whens the last time you saw an 18 wheeler at the inspection station? Where the hell is your reasoning?
> 
> If you take the EGR out your car WILL spark knock. And your car will make 0 NOx with a hole in the piston.


wow. i'm surprised how uninformed some people are, yet make such confident claims.i guess you've never blocked off an egr. burnt piston lol!

i only took my egr out on my other car to make more room under the hood, makes taking off my intake manifold alot easier

reasoning behind the 18 wheeler part is have you ever seen how much smog comes out of older engine on one of those things. thats why i said i dont feel bad taking out my egr and producing 13ppm nox when he puts out like 1000000X that much in one shift.


----------



## bahearn (Jul 15, 2002)

Harris said:


> Bruce, remember you and I had that argument about the EGR?


Uh, no. I've been to sleep once or twice since then...


----------

