Why does my MPG gauge lie to me? - Ford Powerstroke Diesel Forum
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post #1 of 15 Old 02-11-2014, 05:37 PM Thread Starter
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Why does my MPG gauge lie to me?

My digital overhead MPG gauge says I get 18.4 MPG. But if I calculate it based on the trip meter and gallons of full used, I get 14 MPG. Why are they so far off? FYI the 14 MPG was city driving, I had a tank with 17 MPG highway. I'm hoping with the AIS intake upgrade I just did, the 4" exhaust that's on there and the addition of a chip, I can get some better mileage out of the beast.

The reason I ask is, if I get a Kiwi or other OBDII reader, will the MPG readings I get from it be wrong too? (i.e. be the same as my existing gauge?)

2000 Ford Excursion 7.3, AIS intake, 4" MBRP exhaust, PHP Hydra Chip, Bilsteins (5100 in front and 4600 in back) and x code front springs to be added when I can find the time to put them in.

Last edited by MAArcher; 02-11-2014 at 05:43 PM. Reason: add question
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post #2 of 15 Old 02-11-2014, 05:45 PM
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you want to know my opinion?
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post #3 of 15 Old 02-11-2014, 06:06 PM Thread Starter
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Sure, what's your opinion?

2000 Ford Excursion 7.3, AIS intake, 4" MBRP exhaust, PHP Hydra Chip, Bilsteins (5100 in front and 4600 in back) and x code front springs to be added when I can find the time to put them in.
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post #4 of 15 Old 02-11-2014, 06:08 PM
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I drive a lifted 7.3L, I dont want to know what my MPG is LOL

if i knew, i think you will see a grown man cry hahahaha
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post #5 of 15 Old 02-11-2014, 06:46 PM
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I track my mpg.
But not because I care, I track it because a drastic change for no reason is an indication that there is a problem I need to address.

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Dual SD fuel pumps, in tank mods, CNC Fab bowl retain kit. SDK Tunes. Isspro.
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I love finally having my truck back... that 7.3 dog that I was driving was just not cutting it.

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post #6 of 15 Old 02-11-2014, 07:26 PM
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Sorry for hijacking your thread, but is their a way to actually track your MPG while going down the road?

Anybody heard of someone tapping their fuel line with a meter or something? That ways you can actually track how many gallons is used per mile on your trip meter.

Just a thought, maybe one of you engineers could come up with something like that.


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post #7 of 15 Old 02-12-2014, 02:41 AM
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Quote:
Originally Posted by peter379 View Post
Sorry for hijacking your thread, but is their a way to actually track your MPG while going down the road?

Anybody heard of someone tapping their fuel line with a meter or something? That ways you can actually track how many gallons is used per mile on your trip meter.

Just a thought, maybe one of you engineers could come up with something like that.
Mass flow meter. They are expensive though. Just bought one at work and cost 3 grand. Still needs to be calibrated as there is significant viscosity differences between fuel and water (aqueous solutions). Will post a link once I get to work. Not sure what the price difference would be for one that reads truck flow rate range.

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post #8 of 15 Old 02-12-2014, 04:11 AM
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The Torque app monitors your fuel flow. If somebody wrote a formula to factor in fuel flow with distance traveled (tracked by your GPS), you could get a fairly accurate reading.

My Lie -O- Meter has said anything from 10-11.5 mpg. Hand calculated, it's pretty consistent (without a load) around 15.2 mpg.


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post #9 of 15 Old 02-12-2014, 04:15 AM
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post #10 of 15 Old 02-12-2014, 05:35 AM
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Quote:
Originally Posted by AgTires4295 View Post
The Torque app monitors your fuel flow. If somebody wrote a formula to factor in fuel flow with distance traveled (tracked by your GPS), you could get a fairly accurate reading.

My Lie -O- Meter has said anything from 10-11.5 mpg. Hand calculated, it's pretty consistent (without a load) around 15.2 mpg.
Iirc, it uses icp and pw to calculate fuel flow. This is assuming a stock (cc/nozzle size) and healthy injection system.

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