Milage with EGR Open or Closed

richardkf · **Joined:** Wed Jun 14, 2006 4:15 pm **Posts:** 167

I guess it was just a matter of time for me ... but my EGR failed about two weeks ago. When it failed, it somehow caused a boost hose (or this is what they told me) to 'pop off'. After a week at the dealer, replacing the EGR and boost hose clamps, I was told the failed EGR was stuck in the open position.

The CRD feels a little stronger when I accelerate now ... and the MPG has increased a few MPG. What is the relationship of the EGR in the open or closed position to MPG/economy?

dgeist · **Posted:** Tue Jul 01, 2008 8:44 am

richardkf wrote:

I guess it was just a matter of time for me ... but my EGR failed about two weeks ago. When it failed, it somehow caused a boost hose (or this is what they told me) to 'pop off'. After a week at the dealer, replacing the EGR and boost hose clamps, I was told the failed EGR was stuck in the open position.

The CRD feels a little stronger when I accelerate now ... and the MPG has increased a few MPG. What is the relationship of the EGR in the open or closed position to MPG/economy?

I seriously doubt that getting stuck open would give you better performance. Perhaps they got it backwards.

EGR closed == cooler intake temps == more combustible O2 molecules per unit volume == better fuel economy == a little more power
EGR open == hot exhaust gasses in intake == less O2 to burn == less power and efficiency

Uffe · **Posted:** Tue Jul 01, 2008 2:11 pm

dgeist wrote:

I seriously doubt that getting stuck open would give you better performance. Perhaps they got it backwards.

EGR closed == cooler intake temps == more combustible O2 molecules per unit volume == better fuel economy == a little more power
EGR open == hot exhaust gasses in intake == less O2 to burn == less power and efficiency

Addendum, EGTs can also be controlled using EGR. EGR open == lower EGTs.

dgeist · **Posted:** Tue Jul 01, 2008 5:01 pm

Uffe wrote:

dgeist wrote:

I seriously doubt that getting stuck open would give you better performance. Perhaps they got it backwards.

EGR closed == cooler intake temps == more combustible O2 molecules per unit volume == better fuel economy == a little more power
EGR open == hot exhaust gasses in intake == less O2 to burn == less power and efficiency

Addendum, EGTs can also be controlled using EGR. EGR open == lower EGTs.

Yep, forgot that one. To expound a little, I think that was the original idea for EGRs in gasoline engines. On the gasser side, you can actually get a benefit by REDUCING the amount of O2 in the combustion chamber. Something along the lines of less heat for a more complete burn. Also, as mentioned, the exhaust is cooler with the EGR, resulting in less formation of nasty NO2 (IIRC). Someone with more diesel experience please correct me if I'm wrong, but I don't think diesels benefit from ANY of those things with the EGR operating, yes?

Dan

Cowcatcher · **Posted:** Wed Jul 02, 2008 10:53 am

It seems to me that most here who have had EGR failure have had it fail in the open position. The SEGR, or related mods, keep the EGR closed.

richardkf · **Joined:** Wed Jun 14, 2006 4:15 pm **Posts:** 167

dgeist wrote:

richardkf wrote:

I guess it was just a matter of time for me ... but my EGR failed about two weeks ago. When it failed, it somehow caused a boost hose (or this is what they told me) to 'pop off'. After a week at the dealer, replacing the EGR and boost hose clamps, I was told the failed EGR was stuck in the open position.

The CRD feels a little stronger when I accelerate now ... and the MPG has increased a few MPG. What is the relationship of the EGR in the open or closed position to MPG/economy?

I seriously doubt that getting stuck open would give you better performance. Perhaps they got it backwards.

EGR closed == cooler intake temps == more combustible O2 molecules per unit volume == better fuel economy == a little more power
EGR open == hot exhaust gasses in intake == less O2 to burn == less power and efficiency

Thanks for the info - what the dealership makes sense. While it was stuck open, i noticed the CRD had lagged in performance and fuel economy dropped. Now that it is functioning properly - it performs better and milage is back up a few mpg.

Milage with EGR Open or Closed

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