How accurate is the mpg and distance remaining display readout with aftermarket parts?

bthai

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Just wondering how accurate the mpg display readout or the distance remaining readout is after adding after market parts such as intake, exhaust or bigger and wider wheeels?
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Snoopyslr

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My dash is always exactly 2mpg higher than my RL mpg. I'm still running factory tires with aftermarket wheels (same size).

That number is figured out based on vehicle speed (distance traveled) and fuel injector pulse latency (how much fuel is injected). Theoretically, no amount of modifications would change the accuracy of that number unless you change the circumference of the tires or change the displacement of the fuel injectors.
 
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Draken187

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My dash is always exactly 2mpg higher than my RL mpg. I'm still running factory tires with aftermarket wheels (same size).

That number is figured out based on vehicle speed (distance traveled) and fuel injector pulse latency (how much fuel is injected). Theoretically, no amount of modifications would change that number unless you change the circumference of the tires or change the displacement of the fuel injectors.
Its exactly as snoopyslr stated... Also keep in mind fuel reserves.. Once you hit 0 in range.. You can technically go about 30 more miles
 

Snoopyslr

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Its exactly as snoopyslr stated... Also keep in mind fuel reserves.. Once you hit 0 in range.. You can technically go about 30 more miles
I give myself about 30 mile buffer when I hit 0 also. I'll be driving about 15 miles past empty today on my way home before I get to my gas station (across the street from my house).

I've done some testing on that. I believe that the tank hits empty (0 miles) when there is 1 gal left in the tank. I pulled into a station right when it hit 0 and filled it up. I was exactly 1 gal from tank capacity.
 

bhorn

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The MPG reading is not accurate with stock parts, so it might actually be better? :dunno:
 


Draken187

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The MPG reading is not accurate with stock parts, so it might actually be better? :dunno:
Its well within margin of error in my opinion.. Within less than 2% i believe.. Thats alot better than most cars..especially when its a giant math problem that keeps updating itself.. The math problem is trying to estimate what you will have for range based on your driving pattern since you last filled up.. So if you fill up and do 200 miles half city half highway.. It will think it will be the same type of driving for the remainder
 

bhorn

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Its well within margin of error in my opinion.. Within less than 2% i believe.. Thats alot better than most cars..especially when its a giant math problem that keeps updating itself.. The math problem is trying to estimate what you will have for range based on your driving pattern since you last filled up.. So if you fill up and do 200 miles half city half highway.. It will think it will be the same type of driving for the remainder
I'm not talking about the estimated distance, I'm talking about the fuel efficiency indicator, in MPG. It is always 5-10% off versus hand calculation (as evidenced in my fuelly link). Car says 38 MPG... it's actually 36. Always.
 

rabit1111

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Got 44.1 mpg on trip computer. But my calculation only got 42.76 mpg. I pump 10.74 gallons for 459 miles and still have 30 miles left for the range
Honda Civic 10th gen How accurate is the mpg and distance remaining display readout with aftermarket parts? IMG_2019.JPG
 

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For those of us who notice some variance between the car's mpg readout and the hand calculation, .. there could be some reasons for it besides inconsistent fills:

Fuel density variations: temperature, what's in the mix (Shell vs Exxon, winter blend vs summer, etc).
Temperature: high ambient temperatures will result in more unaccounted for fuel purging.

Also of note:
"Honda uses additional inputs to calculate trip mpg. “We look at the fuel-consumed data that comes from the engine-control computer, but we also track the float sensor measuring the fuel level in the tank,” says Raj Manakkal, chief engineer for electrical and infotainment devices. He also points out that, due to temperature changes, plastic fuel tanks can expand and contract by as much as a liter. On the Acura ILX, that yields a total variation of 4 percent."

http://blog.caranddriver.com/why-yo...ving-accurate-mpg-readings-and-how-to-fix-it/
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