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Old 05-27-2014, 02:05 PM   #1
HighTechCoonass OP
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Question Miles Per Gallon... How is display calculated?

Is there a fuel flow meter on our bikes? I do not remember seeing one on the 911 tool.

The reason I ask is if one does a mod (Air temp , pipe, o2 sensor, or sprockets) will the fuel mileage difference (plus or minus) show up?

My driving habits I usually see about 70 mpg at 50mph and about 47 mpg at 70 mph.

I for the record have an Air temp mod (Power Controller) and a Leo Vince pipe - and I see no fuel consumption difference on the display or on fill ups at the pump. I also check against a friend who has a stock bike. Our consumption is exactly the same.

My miles to empty has also been very very accurate based on volume to top off the tank.

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Old 05-27-2014, 03:33 PM   #2
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Originally Posted by HighTechCoonass View Post
Is there a fuel flow meter on our bikes? I do not remember seeing one on the 911 tool.
Most of these fuel economy meters are based on injector pulses. The amount of gasoline entering the engine with every injector pulse is known, and so is the number of pulses per second as well as the distance traveled during that time.
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Old 05-27-2014, 03:51 PM   #3
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yep that would get you close....

one thing though...

The amount of gasoline entering the engine with every injector pulse is known... relatively yes but the "pulse time on" would be determined by Air box temp (in open loop) or the o2 readings (in close loop)


I guess then using this theory if you used an 02 shift'er on a long highway run the economy readings would be off...

As well as a AIT spoofer with lots of throttle movement the values would be off...


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Most of these fuel economy meters are based on injector pulses. The amount of gasoline entering the engine with every injector pulse is known, and so is the number of pulses per second as well as the distance traveled during that time.
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Old 05-27-2014, 04:28 PM   #4
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I just did a 1,000 pavement ride. The bike has an Af-Xied, set at 13.8 afr plus an Accelerator module and a Leo Vince exhaust.

I was running a 17 tooth sprocket just to see what the mileage was going to be. A tank at 70/75mph (with camping gear) was the worst at 46mpg.

The best was running down hill from Tahoe to home that got 58mpg at 65mph.

The rest was in between. We ran a lot of obscure mountain roads with little traffic. The speed wasn't high, but there was a lot of throttle twisting.

I didn't see much difference with different gearing, with or without a spoofer, except for the fueling set up I have, got a small mileage gain at low speed.

We did spend a lot of time at altitude. The freeway mileage was on 101.

I see more mileage differences, every time California changes it fuel formula.
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Old 05-27-2014, 05:41 PM   #5
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Laugh

I did a little reading on the internet so this must be right.

The computer uses the time the injectors are energized (with known fuel pressure) and compares to miles traveled. That makes sense.

That would mean that your mileage calculation would stay correct with any mods attached.
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Old 05-27-2014, 07:54 PM   #6
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Originally Posted by HighTechCoonass View Post
I did a little reading on the internet so this must be right.

The computer uses the time the injectors are energized (with known fuel pressure) and compares to miles traveled. That makes sense.

That would mean that your mileage calculation would stay correct with any mods attached.
Now you've for it exactly right. As long as you don't alter the fuel pressure or change the injectors or change the wheel size, the trip computer calculates mileage accurately by keeping track of the total on-time of the injectors and the miles ridden.
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Old 05-27-2014, 09:01 PM   #7
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My speedometer reads about 10% fast, but the mpg read out is always within a few 10ths. I haven't checked the oldometer, but I would have to assume that it is correct.
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Old 05-28-2014, 12:35 AM   #8
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I did 300 miles on Sunday. Filled up 2x & kept track of the mileage at each fill up. Display said 50 mpg, calculation based on gas filled = 50 mpg. So I conclude mines accurate.

Don't know why I consistently get 45-50 mpg. Some folks get better.


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Old 05-28-2014, 07:04 AM   #9
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My speedometer reads about 10% fast, but the mpg read out is always within a few 10ths. I haven't checked the oldometer, but I would have to assume that it is correct.
Your speedo is dead accurate EXCEPT that the needle shows low/high due to production variances when positioning the needle on assembly. It can be tweaked. The computer uses all sensors to calculate data but has no clue that the needle is a hair off. It's just a pointer. That's why MPG and ODO are correct despite the speedo telling lies.
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Old 05-28-2014, 08:05 AM   #10
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there's legislation in many jurisdictions that require that a speedo may read high but must never read low.
Hence they tend to be optimistic.
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Old 05-28-2014, 08:41 AM   #11
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The MPG also seems to be a bit pessimistic.

I have been on rides where I get mileage higher then reported based on the fuel required to fill the tank.
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Old 05-28-2014, 01:07 PM   #12
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Your speedo is dead accurate EXCEPT that the needle shows low/high due to production variances when positioning the needle on assembly.
In addition, there are EU and UNECE directives that state that your speedo can never read low, but is allowed to read high. So, vehicle manufacturers will always err on the side of caution, and will just make the speedo read high by design.

http://en.wikipedia.org/wiki/Speedometer#Error
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Old 05-31-2014, 05:22 AM   #13
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I noticed my computer calculates mpg lower than comparing miles to how many gallons I fill up. Comp says I get 45-50 on avg while if I take my mileage traveled and divide by gallons I put in, I get around 60.

Something else thats odd is when I reach reserve (the light comes on) my display starts counting mileage UP. The highest ive seen it go was 40. I thought once the reserve light goes on the display was supposed to tell me how many miles until empty. Please correct me if I'm wrong.

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Old 05-31-2014, 06:16 AM   #14
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Something else thats odd is when I reach reserve (the light comes on) my display starts counting mileage UP. The highest ive seen it go was 40. I thought once the reserve light goes on the display was supposed to tell me how many miles until empty. Please correct me if I'm wrong.

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Old 06-01-2014, 11:55 AM   #15
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Something else thats odd is when I reach reserve (the light comes on) my display starts counting mileage UP. The highest ive seen it go was 40.
What you describe is perfectly normal. That's how these bikes work nowadays. Once the low fuel light comes on, it's basically just a miles counter, letting you know how far you've traveled on the reserve fuel. I wouldn't push it much past 40, but they're all calibrated differently, so YMMV.
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