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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > I notice a lot of talk about gas mileage in Rev II reviews, how are you calculating?



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      02-11-2009, 01:22 PM   #1
E82tt6
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I notice a lot of talk about gas mileage in Rev II reviews, how are you calculating?

Are people using the onboard computer, or a calculator? Since installing the JB3 (and even stock) I found the onboard computer to be COMPLETELY unreliable, and always relied on a calculator for my MPG numbers.

I was just curious, as I believe Shiv stated he toned down injector duty cycle, but increased fuel pressure during crusing to promote a more efficient burn, and the lowered duty cycle on the injectors would also show a disproportionately better MPG reading on the onboard computer, if I understand how it works.

This is NOT a tuner bashing or tuner war thread, please don't make it into one. I'm just curious, as I've noticed this is a common theme in Rev II reviews.
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      02-11-2009, 01:43 PM   #2
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Originally Posted by E82tt6 View Post
Are people using the onboard computer, or a calculator? Since installing the JB3 (and even stock) I found the onboard computer to be COMPLETELY unreliable, and always relied on a calculator for my MPG numbers.

I was just curious, as I believe Shiv stated he toned down injector duty cycle, but increased fuel pressure during crusing to promote a more efficient burn, and the lowered duty cycle on the injectors would also show a disproportionately better MPG reading on the onboard computer, if I understand how it works.

This is NOT a tuner bashing or tuner war thread, please don't make it into one. I'm just curious, as I've noticed this is a common theme in Rev II reviews.
The only time we raise fuel pressure is above ~50% throttle so during cruise and light load. And the extra ignition advance is only there up to 1 to 3psi (depending on rpm). So the on-board computer should be as reliable just as long as you are driving conservatively (little to no boost). So that 35-40mpg people are seeing during 55-65mph cruise is legit as can be.

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      02-11-2009, 02:02 PM   #3
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ive always got 230-260 to a tank on my weekly drive to work. Traffic and some fwy. The Past 2 tank since loading the new maps, i have managed a 290 and 310miles. All i do is reset the odometer to zero when i fill up and head back to the gas station when the car is at 10 miles remaining or so.
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      02-11-2009, 02:05 PM   #4
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ive always got 230-260 to a tank on my weekly drive to work. Traffic and some fwy. The Past 2 tank since loading the new maps, i have managed a 290 and 310miles. All i do is reset the odometer to zero when i fill up and head back to the gas station when the car is at 10 miles remaining or so.
This is a very good and valid data point since the only difference between the new v3.2 beta and the old v3.1 maps is the extra timing advance and revised AFR during cruise. The fuel pressure maps haven't changed in ages.

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      02-11-2009, 02:20 PM   #5
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Quote:
Originally Posted by shiv@vishnu View Post
The only time we raise fuel pressure is above ~50% throttle so during cruise and light load. And the extra ignition advance is only there up to 1 to 3psi (depending on rpm). So the on-board computer should be as reliable just as long as you are driving conservatively (little to no boost). So that 35-40mpg people are seeing during 55-65mph cruise is legit as can be.

Shiv
wow, that's great news because I noticed a huge improvement in my mellow commute from 15mpg with the 3.1 december maps to 18mpg with the latest 3.2 maps. I had assumed it was because of the fuel pressure mapping but it sounds like that's not the case since I was never above 30% throttle on this particular commute.
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      02-11-2009, 05:27 PM   #6
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I also reset my trip odometer at fill ups and have been getting about 30-40 miles more per tank since swithcing to the 3.2 maps.
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      02-12-2009, 12:09 AM   #7
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Ok, was curious.
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      02-12-2009, 01:09 AM   #8
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+1...

saw about 35mpg on highway, 30.5 mpg combined this tank
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