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Old 09-10-2018, 03:40 PM   #1 (permalink)
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Join Date: Apr 2011
Location: Southern France
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AX - '95 CitrŲen AX

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Can you help me understand my "MPG vs gear" results ?

Hello everyone,
I purchased a Peugeot 307 SW from 2004 last year, it has the 2.0 HDI (diesel common rail injection) engine with 136 hp. For my curiosity, I have done some consumption experiments where I drove 50 mph (new speed limit in France on roads) in various gears, from 3rd to 6th. As measurement, I had the factory screen indicator and also a laptop with software to communicate with the ECU (fuel injected per cycle, rpm, fuel pressure... lots of parameters). In theory, they should be identical since they take the infos from the same sensors. The test road was 4 km long, flat and straight. I did for each gear a run in each direction. Data acquisition was started and stopped between 2 signs, I was already in cruise control a few hundred meters before the start. The results are surprising. I expected something where I gained much from 3rd to 4th, a bit less from 4th to 5th and again a bit less from 5th to 6th.
True for 3rd and 6th, obviously. But MPG was better in 4th than 5th

Following figures are the averages of about 500 values in both directions.

Gear-----mg injected per cycle-----rpm-----speed-----calculated l/100---OBC l/100-

Couldn't use cruise control in 3rd gear, that's why speed is slighty higher. I can't think of anything during the test that could explain that, conditions were really the same all over.

Any thoughts ?

CitroŽn AX 1.5 D 430.000 km
Peugeot 307 SW 2.0 HDI 136 195.000 km

Last edited by HypermilerAX; 09-10-2018 at 03:55 PM..
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