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Old 10-24-2011, 01:40 PM   #1 (permalink)
UFO
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Diesel EGR Defeat

I finally pulled the trigger and built my EGR defeat circuit, and installed it this weekend. I'm still tweaking the MAF output to reflect the amount of EGR flow the ECM needs to see in order to not trigger the CEL, but the hardware is now in place.

When I get it configured where I want, I will be doing ABA fuel mileage testing. I had hoped to use my Scangauge to calculate trip mileage, taking note of the following data to facilitate comparison between data sets:

Initial coolant temperature
Ambient air temperature
Miles traveled (will only be commute, with no deviations)
Average speed
Scangauge reported average MPG

Unfortunately the Scangauge doesn't like the new mod. The lack of EGR flow must be affecting how fuel use is reported. Typically on my a.m. commute I average 36mpg or so. With the EGR defeat in place, the Scangauge reported 56mpg on todays commute.

Something tells me my little device has not improved my mileage by 55%. Anyone have any ideas for the scangauge or other methods for documenting fuel mileage?

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Old 11-28-2011, 06:15 PM   #2 (permalink)
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No baselines yet. I had my device miswired, and managed to borrow an oscilloscope to troubleshoot; it seems to be working properly now.

The first thing I have noticed is the engine warm-up is MUCH slower. I am usually up to temperature within 5 miles of driving my commute, but with EGR disabled it takes almost 10 miles of driving.

My baseline will have to involve plugging in the block heater. Obviously the EGR cooler does a considerable amount of preheating the coolant before the engine is warm. Maybe a judicious reroute of the exhaust through the cooler back into the exhaust (instead of the intake) is in order; this could ensure a fair FE baseline, but is a complex endeavor.

I think I have hit on the reason most people claim defeating the VW TDI EGR will reduce fuel economy.
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Old 11-29-2011, 12:42 AM   #3 (permalink)
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Interesting.

I have the 2.0 L CR TDI in my Multivan and already had an issue with EGR (valve defective, had to be replaced with an attached EGR cooler. Was done under warranty, otherwise it would have been around 1k€ oO), so I went and looked if a delete was possible after warranty is up.

But: no way. This was possible in T4 Vans of your vintage, but the T5 (and especially the T5.2) are so wired that deleting the EGR leaves the engine in a non-operable condition. Or you would have to make up a complete ECU.

Furthermore, deleting the EGR seems to bring 2 benefits but also two big no-nos:

- less hassle & repairs
- more power when engine is warm

but:

- higher NOx emissions
- higher fuel consumption

For me, the decision goes in the direction 'keep EGR' (as if I had a choice...). I only wish my new valve will hold up for more kilometers than the previous one (35.000 km). They said they installed the all new & improved type of valve. Lets see.

so long,

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Old 11-29-2011, 02:26 AM   #4 (permalink)
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My engine didn't have an EGR cooler, but about a year ago I installed one from a newer (EURO 4) version. It's hard to tell whether warm-up times shortened, since at the same time I had a block heater installed, plus I added an upper grille block and engine insulation for the winter.
I read that the EGR valve on my engine doesn't open until the coolant reaches a certain temperature, probably to reduce the risk of condensation. Newer, more emissions-centered, versions may start EGRing earlier.

As for milage, I didn't notice any immediate changes, maybe because right after installing the EGR cooler we had a long and cold winter. This year's milage has improved, but I like to blame that on fine-tuning the nut behind the wheel

I don't know if the cooler helped NOx, since my inspection garage doesn't do emissions
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Old 11-29-2011, 10:46 AM   #5 (permalink)
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I'm more familiar with larger diesel engines, but I've never, ever seen any data showing a fuel economy benefit from EGR in a diesel (with all the same engine settings otherwise). In some cases there can be a fuel economy benefit in a gasoline engine, but that's a separate discussion. The thing to watch out for is whether your change to the EGR affects the ECM in such a way that it reacts by changing other things (like timing). IMO, that's where people are probably seeing the fuel economy penalty--it's not directly from removing the EGR--it's from the ECM's reaction. Knowing what the ECM is going to do is a pretty complicated matter in modern ECMs. I know for diesel trucks there are a lot of sims, chips, & programers to remove EGR in such a way that the other engine settings are negatively affected. There are probably similar things out there for the TCI engine. You might want to look into them, but be forewarned that there's a lot of crap out there too.

Yes, warm up time will be longer without an EGR cooler. The block heater is a good way to go (even with EGR). Another thing would be to block off more of the grill. That doesn't really help initial warm up mich becasue the thermostat is closed, but your required cooling load under warm conditions will be decreased so you no longer need as much radiator.

I also started another thread recently to deal with this using an exhasut heat exchanger:
http://ecomodder.com/forum/showthrea...art-19607.html
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Old 11-29-2011, 12:17 PM   #6 (permalink)
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Many at Fred's TDI Page. TDIClub.com. VW TDI Enthusiast Community have tried this.
The only positive is a slight top end gain.
One (don't remember who) drives long enough to eliminate the warm up issue.

Why are you wanting to delete it ? Intake/intercooler restriction/crud ?
Changing the PCV to vent into a can instead of the intake will nearly eliminate the intake crud. With no oil to stick to the EGR soot just goes right through.
YMMV
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Old 11-29-2011, 01:26 PM   #7 (permalink)
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Quote:
Originally Posted by Diesel_Dave View Post
I'm more familiar with larger diesel engines, but I've never, ever seen any data showing a fuel economy benefit from EGR in a diesel
I don't remember where I read it (maybe here?), but in a diesel increasing EGR only works up to a certain point - first it reduces NOx without compromising performance, but then everything starts to fall apart.

Quote:
Originally Posted by Diesel_Dave View Post
(with all the same engine settings otherwise)
Exactly!

Quote:
Originally Posted by Diesel_Dave View Post
I know for diesel trucks there are a lot of sims, chips, & programers to remove EGR in such a way that the other engine settings are negatively affected. There are probably similar things out there for the TCI engine. You might want to look into them, but be forewarned that there's a lot of crap out there too.
I believe this is what the OP is attempting to do: cut EGR while emulating sensor readings for the ECU's sake to make it think everything is OK. I wonder what the effect will be? Since the ECU will think that the intake air is partially emissions, the fuel dosage/timing will be changed accordingly, compared to an intake charge of clean air.
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Old 11-29-2011, 01:40 PM   #8 (permalink)
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Quote:
Originally Posted by JasonG View Post
Many at Fred's TDI Page. TDIClub.com. VW TDI Enthusiast Community have tried this.
The only positive is a slight top end gain.
One (don't remember who) drives long enough to eliminate the warm up issue.

Why are you wanting to delete it ? Intake/intercooler restriction/crud ?
Changing the PCV to vent into a can instead of the intake will nearly eliminate the intake crud. With no oil to stick to the EGR soot just goes right through.
YMMV
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.
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Old 11-29-2011, 01:47 PM   #9 (permalink)
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EGR lowers the specific heat ratio of the combustion stroke gasses. This drops the efficiency of the diesel cycle.

you can see what sort of effect this has by changing g here

The Diesel Engine

(note just plug one nubmer in and the rest will be set to their defaults)

for pure air g would be equal to 1.4 . Typically combustion gases with excess air are about 1.35 . Combustion gases with no excess air are about 1.3 .

However adding EGR if employed in just the right amount at just the right amount for a specific fuel mass injected and a specific rpm can better approximate the idea diesel cycle. This will increase efficiency some. The trick is getting just that right amount.

Now days EGR is mainly just used for NOx control.
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Old 11-29-2011, 02:44 PM   #10 (permalink)
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Quote:
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.

This is the whole reason for the EGR vs SCR debate on diesels (see article here: http://fleetowner.com/management/feature/scr_egr_0701/). An engine with EGR has lower NOx emissions, but worse FE. SCR can clean up the NOx after it's left the engine, but not having to use EGR buys you FE. Of course SCR means you have to add DEF (diesel exhaust fluid).

If EGR improved diesel FE, SCR would have both DEF and worse FE, so there would be no point.

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Last edited by Diesel_Dave; 11-29-2011 at 03:18 PM..
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