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Old 11-29-2011, 03:26 PM   #11 (permalink)
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Quote:
Originally Posted by Diesel_Dave View Post
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Originally Posted by UFO View Post
... when the CEL is lit, the ECM will retard the timing to avoid the creation of NOx and mileage will decrease.
Bingo! there's your reason for FE getting worse by removing EGR.

EGR wil improve FE at the same NOx level, however, if all the other engine settings are the same, I have never, ever seen FE improve with EGR on a diesel.

There's lots of research out there on this, here's one research paper:http://www.iaeng.org/publication/WCE...p1548-1552.pdf

Note that the legend is incorrect (it says brake thermal efficiency when it should say brake specific fuel consumption)
Figure III is the one you want to look at. Note that higher EGR always increases BSFC.
That is an interesting paper. I do wish they had provided enough excess air to burn the fuel completely even at higher levels of EGR; that would seem more fair. Of course, that might have adversely impacted the NOx production, I cannot divine the intent of the author in that regard. Then again, the test engine is not equipped with turbo, so extra air is hard to come by.

The paper's conclusions seem simple enough given the data, and that's why I want to demonstrate a measurable fuel efficiency gain on the TDI. This same type of EGR defeat has been done for the US model of the Jeep Liberty CRD (Cherokee in Europe), and although my wife drives one, I have not tested its fuel efficiency. Others who installed that circuit claim a 10% improvement in mileage, but it is undocumented.

I can believe it makes a significant difference though, as for some reason the US model CRD controls a huge amount of EGR. I pulled the MAP sensor when I first bought it, and with 30k miles it was completely encrusted with oil/EGR accretion. That Jeep had EGR defeat installed around 45k miles, and now has 95k miles. Probably time to check the MAP sensor again, although when it gets gunked up, engine operation is noticeably affected.

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Old 11-29-2011, 03:39 PM   #12 (permalink)
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I have done extensive searching and reading on Fred's site. No one has done due diligence in demonstrating fuel mileage changes with EGR removal. This should involve imitating the conditions of EGR to the computer so it makes no changes in how it fuels the engine -- when the CEL is lit, the ECM will retard the timing to avoid the creation of NOx and mileage will decrease.

To answer your question, I want to convince myself removing EGR improves engine efficiency. I hypothesize it will, and I want to demonstrate it in fact, with as much control over the experiment as I can get.

And secondarily, to keep the intake from clogging. Many on Fred's site make the claim the newer diesel fuels will keep this from happening. I pulled my intake and cleaned it two years ago, and it was a mess. I may do it again in the spring and see if there is appreciable buildup. I am not sure the new diesel fuels are any different in that regard. And I also don't believe you can remove enough of the oil in the intake to prevent the crud from sticking; if there is a fuel efficiency gain from removing EGR, that is the better solution for me.
Many on Freds site don't get CELs as they defeated the EGR through software. They still get nasty intakes.
My 94' doesn't send crankcase vapors through the intake, light coating of powder. It ran for years on regular "high sulpher" diesel.

Again YMMV
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Old 11-29-2011, 03:43 PM   #13 (permalink)
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My 94' doesn't send crankcase vapors through the intake, light coating of powder. It ran for years on regular "high sulpher" diesel.

Again YMMV
Where is the blowby routed? Every diesel I've seen vents the crankcase to the intake. Not that I'm familiar with a lot of engines, just the TDI, the VM Motori CRD and the Mercedes OM617 engines....
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Old 11-30-2011, 02:28 AM   #14 (permalink)
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Where is the blowby routed? Every diesel I've seen vents the crankcase to the intake. Not that I'm familiar with a lot of engines, just the TDI, the VM Motori CRD and the Mercedes OM617 engines....
Same with PSA's HDi turbodiesels.
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Old 11-30-2011, 06:35 AM   #15 (permalink)
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The messy and not real good for the enviroment answer is to pull the hose and put a filter end on it. Most race shops have them. Looks like a pod filter but onlt abouy an inch or so in diameter.

The better way is to route it to a small catch can then to the mini pod. This keeps the oil from dripping all over.

I guess you could put a few screens in the catch can and route the now dry vapors to the intake for emission reasons ?
Most diesel heads are anal about clean air to prevent turbo pitting yet will send droplets of oil into it ? Never really understood that.
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Old 11-30-2011, 07:48 AM   #16 (permalink)
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Bingo! there's your reason for FE getting worse by removing EGR.
Why don't they keep the EGR valve somewhere under the hood, but not connected to the exhaust or intake ?
I.e. working, but not functional, so it won't throw fault codes.

There's usually no EGR flow measurement, or is there ?
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Old 11-30-2011, 09:05 AM   #17 (permalink)
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Why don't they keep the EGR valve somewhere under the hood, but not connected to the exhaust or intake ?
I.e. working, but not functional, so it won't throw fault codes.

There's usually no EGR flow measurement, or is there ?
In some cases that can be done, but it depends on the sophistication of the fault detection software. Some ECM's probably just look to see if the valve is moving, others look at intake pressure, intake temp, exhaust pressure, etc. and see if it's consistent with the amount of EGR it thinks it's sending.

In some cases there's a deltaP sensor in the EGR loop that's used to estimate EGR flow. In some cases EGR flow is estimated based on a MAF sensor (fresh air flow) - total charge flow (estimated from speed, IMP, & IMT).

In some cases it has a "primary" estimate based on one set of measurements, and a "secondary" estimate based on another set of measurements. The primary estimate is used for controls, but if the secondary estimate isn't within a certain amount of the primary, it trips a fault code.

It all depends on how the software is set up.
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Old 11-30-2011, 09:57 AM   #18 (permalink)
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Quote:
Originally Posted by euromodder View Post
Why don't they keep the EGR valve somewhere under the hood, but not connected to the exhaust or intake ?
I.e. working, but not functional, so it won't throw fault codes.

There's usually no EGR flow measurement, or is there ?
While not a diesel my 99 maxima had a CEl with a code for egr flow volume. The supply tube from the exhaust was plugged. Cleaned the tube and cleared the code, no further codes.
No reason why a US emissions spec diesel would not have the same OBD2 code as a 12 year old Maxima.

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Old 11-30-2011, 03:04 PM   #19 (permalink)
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Most diesel heads are anal about clean air to prevent turbo pitting yet will send droplets of oil into it ? Never really understood that.
I read somewhere that a small amount of oil getting thrown at the turbo with the intake air will help lubricate it. On the other hand, every turbodiesel I've seen has the whole intake track "sweating" oil, so I doubt that this amount is small, or that it doesn't effect emissions.
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Old 12-01-2011, 09:15 AM   #20 (permalink)
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How are you mitigating the increased NOX production now that the EGR is disabled?

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