EGR and efficiency

We always hear how disabling EGR increases efficiency. It might be due to other factors, like clogged intakes at the same time etc. With oil separation or elephant hose CCV to air, EGR might be helpful at low loads:

I see some studies where EGR helps reduce consumption under low loads, so I am confused.

https://www.researchgate.net/profil..._-A_REVIEW/links/55502cae08ae739bdb90cf3c.pdf
Page 6, bottom right more efficiency with egr used.

https://www.researchgate.net/figure/216832254_fig3_Figure-3-EGR-influence-on-BSFC shows egr reduces bsfc- more efficiency but i dont know the load here


So if EGR can help efficiency at low loads, that explains why my all time best tanks were before I disabled egr?

Thanks Lee. I recall reading that thread before. The adaptation is another variable that affects things. I think it changes some other things like timing but I'm not sure.

In my case I fully tuned it to turn off egr when warmed up. It doesn't affect the other things like timing etc.

I will do some testing this weekend.

Ran a few tests comparing EGR on and off.

Fully warm engine.
I put headlights on, defroster on, AC on full high and let the load stabilize.
I unplugged the egr vac line and plugged it with a screw to disable EGR.
I also tested with using adaptation to make it so high that EGR is off too, same results.
Egr on around 360 mg/s
Egr off around 480-490 mg/s.



At normal idle speed- 903 rpm:
IQ with EGR - 9.5 or so.
IQ without EGR- 10.2

At high idle, hold brake and gas for 1200 rpm:
IQ with EGR - 7.5
IQ without EGR - 7.8-8.2 fluctuating

Both cases, the EGR on uses less fuel.

It pretty much makes sense because there is less back pressure and I run typical idle SOI of 3.5 btdc.

You can't compare data like that since the ECU is still wanting the EGR to work. It knows what the idle MAF needs to be, and see's much higher. My guess, it throws everything out of whack as the ECU tries to get more EGR flow.

FordGuy100 said:

You can't compare data like that since the ECU is still wanting the EGR to work. It knows what the idle MAF needs to be, and see's much higher. My guess, it throws everything out of whack as the ECU tries to get more EGR flow.

Click to expand...

I'm retuned with dynamic EGR but now adjusted to only turn off EGR if the engine temperature goes too high (100C). I also have a timing vs coolant temp map to cut timing above 100 C.

Also, I am not running the stock EGR, but 50 more maf for when I hit operating temperature. I don't think a high rate of EGR is efficient either. But what it does do is reduce backpressure for the same boost, because the turbo does work based on pressure X flow. In the ecuconnections economy thread, reducing cruising boost to atmospheric loses efficiency as some have tested. So, that's why I run close to stock boost request below 20 iq (low loads).

All other tables that deal with egr are not stock. I run some extra advance. I can unplug my EGR or n18 while it asks for EGR and get no CEL or code.

I can repeat the test with reflashing absolutely no EGR used but I know I have no maps that change timing based on EGR/airflow.

yatzee said:

http://forums.tdiclub.com/showthread.php?t=305248

Click to expand...

Yep, that helps economy because warmup is much faster with EGR on putting heat into the coolant!
I've had that for years, since I got my own MPPS cable. It's a pretty easy mod.

But, don't we lose efficiency in cruise if we have the boost low, as you and some others noticed (less dynamic compression at low load)?
I figure if we need this extra pressure, with EGR the turbo doesn't work as hard, as you say.


Ok, I did this today. Unplugged the vac line to turbo and did EGR on versus off.
So, we eliminate the backpressure issue.

Hotter day today, so higher IQ for the load of AC + headlights + defroster.

At normal idle speed:
IQ with EGR - around 10.6
IQ without EGR- around 10.9

At high idle, hold brake and gas for 1200 rpm:
IQ with EGR - around 8.5
IQ without EGR - around 8.9

Similar dynamic. Of course this is not normal cruising levels at 1200 rpm, but I don't have a long enough commute to come up with a consistent road test.

I'm not running the stock EGR level when warm, but +50. So a bit less EGR than stock. I also have the EGR cooler, but I may change back to the uncooled EGR pipe one day because the stock ALH egr is a hard fit on the PD150 intake manifold. My mount is working now, but if it breaks, it ends up damaging the flex pipe.



We talked a bit in another post about excess air. If there is AFR above mid 20's that is ideal, especially low-mid loads, from what I read in the past.
So with my test, 360mg/s with 10 IQ, that's 36 AFR, still excess air. Without EGR its 49 AFR!
So maybe the key thing to benefit from EGR is to not go as extreme as the stock setting which tries to maximize it to cut NOx.