Why Does Cleaning The EGR Help MPG ?

[200bhp]

I have read up and subsequently cleaned the EGR mixer on my D5 XC90 and according the the computer the mpg has improved.

Can anyoine explain what exactly the EGR does (I know it recirc exhaust gas) but why is this benificial ? Presumably it must be if cleaning the mixer allows more EGR ands gives better mpg.

Or does cleaning just affect some sensor giving the illusion of better mpg ?

Also if EGR is beneficial why do I read of people blanking it off ?

Thanks

[Bernard333]

My D5 with 127k miles was well clogged up , I did get some enjoyment cleaning out the gunge thinking it would help and it was really bad but I cant honestly say its made any difference to performance or fuel consumption but my car has a lot of other problems as well so maybe on a car with everything else working as it should it does make a difference , I am about to remove the intercooler followed by the turbo to check for problems on mine and I even suspect the cat may be done . I think you can blank off the egr as its supposed to improve the power slightly but there is always a downside and that is the the egr duct gets blocked completely and causes more problems .

[tykey]

People sometimes blank off EGR's because of really smoky exhausts. If you've got a really worn engine, then it makes combustion even worse and makes MORE smoke. Blanking it off can substantially reduce this.

[200bhp]

I had a quick look on Wiki and it seems quite a good reply albeit seeming to conflict with various posters results.

Exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in most gasoline and diesel engines.

EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. Intermixing the incoming air with recirculated exhaust gas dilutes the mix with inert gas, lowering the adiabatic flame temperature and (in diesel engines) reducing the amount of excess oxygen. The exhaust gas also increases the specific heat capacity of the mix, lowering the peak combustion temperature. Because NOx formation progresses much faster at high temperatures, EGR serves to limit the generation of NOx. NOx is primarily formed when a mix of nitrogen and oxygen is subjected to high temperatures.

In modern diesel engines, the EGR gas is cooled through a heat exchanger to allow the introduction of a greater mass of recirculated gas. Unlike petrol engines, diesels are not limited by the need for a contiguous flamefront; furthermore, since diesels always operate with excess air, they benefit from EGR rates as high as 50% (at idle, where there is otherwise a very large amount of excess air) in controlling NOx emissions.

Since diesel engines are unthrottled, EGR does not lower throttling losses in the way that it does for petrol. However, exhaust gas (largely carbon dioxide and water vapor) has a higher specific heat than air, and so it still serves to lower peak combustion temperatures; this aids the diesel engine's efficiency by reduced heat rejection and dissociation. There are trade offs however. Adding EGR to a diesel reduces the specific heat ratio of the combustion gases in the power stroke. This reduces the amount of power that can be extracted by the piston. EGR also tends to reduce the amount of fuel burned in the power stroke. This is evident by the increase in particulate emissions that corresponds to an increase in EGR. Particulate matter (mainly carbon) that is not burned in the power stroke is wasted energy. Stricter regulations on particulate matter(PM) call for further emission controls to be introduced to compensate for the PM emissions introduced by EGR. The most common is particulate filters in the exhaust system that result in reduced fuel efficiency. Since EGR increases the amount of PM that must be dealt with and reduces the exhaust gas temperatures and available oxygen these filters need to function properly to burn off soot, automakers have had to consider injecting fuel and air directly into the exhaust system to keep these filters from plugging up.

[LJD]

I have deleted (blanked off) the EGR on my golf, landcruiser and Pug that i owned . Best thing i ever did !
Once i have my V70 (tomorrow) i will be exploring how it can be done also .

I have never like EGR's

[popuptoaster]

Its like pretty much all the rest of the emmisions gear, take it off for more power but a dirtier car, cars have been saddled with this stuff since the 60's it just changes form and gets more efficient.

[BillB]

I would have thought that blanking the egr would post a fault code (egr flow too low).

[outnumbered]

depends on what year the 2002/2003 you can get away with no warnings but it can still cause issues further down the line. the 2004 onwards throws a fault straught away.
mike

[Helibatics]

Do EGR valves soot up due to driving habits or do they all eventually all block up?

I took mine out to clean it because the car had done 110k miles and I expected a very gungy valve.

I was surprised that the EGR valve itself was clean. The manifold after the valve had some deposit though, which I scraped out.

All cleaned and reassembled and I can't tell any difference in performance or MPG. I do have a warm feeling knowing that it's not dirty though :-)

[hamster]

I've been thinking of cleaning mine out. Just clocked 150k so there must be a fair level of crud built up in the pipeworks.

Changed the intercooler last year and that made a big difference.