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Old 01-27-2015, 06:49 PM   #75 (permalink)
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Join Date: Oct 2008
Location: Chile
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Mercedes 89 D - '89 Mercedes 300 E
90 day: 33.86 mpg (US)

Skodie - '09 Skoda Octavia TDI PD
90 day: 38.84 mpg (US)

1993 Mercedes 300D Turbo - '93 Mercedes Benz 300D Turbo W124
90 day: 26.19 mpg (US)

Crossie - '16 Subaru XV Crosstreak
90 day: 9.61 mpg (US)

Crossie - '16 Subaru XV Crosstreak
90 day: 33.34 mpg (US)
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Better fuel economy with EGR

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 (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:
Here you have your first: My 1993 Mercedes turbo diesel has a EGR device. Almost all people think (as I did), that cancelling the EGR will produce better power and better FE. "Go for it" said my mechanic. And I did. I was dissapointed with the result: my mileage went worse. Then I connected it back, and my mileage went better! (Please look at my fuel log).

But lets face it: almost no one comes with hard figures, just mere opinions, preferences, "it should be so and so, because of that" kind of thoughts.

I wanted a positive outcome. But I didn't get it.

All know that the only valid and correct way to test the effect of EGR is to MEASURE with a onboard fuel computer. Like MPGuino or other.

Driving a full tank of fuel and compare with another is not valid. I drive about 600 km even 900 km with 70 liters of diesel. FE is determined greatly by traffic, speed, slope, payload, tire pressure, general temperature, even air humidity. Not to mention driving strategy, which per se can vary FE as much as 40%! Specially if you want your hypothesis to win over the other's one.

How to measure then? The correct procedure is to compare FR with EGR vs without EGR, keeping all other conditions constant between measures. Of course that is imposssible (and very expensive by the way, if you need to drive so long to get outcomes) if you will travel 700 km.

What I want to see is a test of, say, 1 km drive at a steady speed (better with cruise control) on a flat pave, forth and back, and take the mean, to eliminate wind, little slopes, etc. keeping all the rest "ceteris paribus".
Do it with EGR operative and again witout it. Then you can compare.

I have done this kind of tests on a Skoda diesel TDI, which has an onboard computer, and believe me that real time fuel economy varies a lot. So much that I had to use mean fuel economy only.

Unfortunately, very few people devote time to make this kind of tests, seriously, and prefer to just give their opinions. Unfortunately also, my 1993 Mercedes turbo diesel don't have an onboard computer, but I will install a MPGuino and hope it will give a good estimate of fuel economy, at least, for comparison and testing purposes.


Mercedes 300 D turbo 1993

Last edited by oldbeaver; 01-27-2015 at 06:54 PM.. Reason: improving clarity
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