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Fuel economy accuracy

Jdreg

Ready to race!
Wondering if there’s a general consensus about how much the computer generated fuel mileage is off. Would it be a consistent 1-2 mpg to high, for example, for most of the cars. Or is inconsistent from one car to another.
Thanks
 

IWMTom

Autocross Newbie
Wondering if there’s a general consensus about how much the computer generated fuel mileage is off. Would it be a consistent 1-2 mpg to high, for example, for most of the cars. Or is inconsistent from one car to another.
Thanks

Mine is out by between 10 and 15%, so I corrected it by 13% for a slightly more accurate readout..

The computer can never be accurate, though.
 

Tsi7

Ready to race!
Location
Ontario, Canada
Mine was about 7% optimistic... Adjusted with obdeleven and its pretty close... Usually +/- 0.2 liters per hundred after doing hand calculations... Sometimes it's bang on. All depends on when the pump clicks off too which will effect the accuracy
 

SRGTD

Autocross Newbie
Location
UK
The computer can never be accurate, though.

Agree, it will only give an indication of fuel consumption.

Calculating the fuel consumption manually over the long term will be more accurate, but this method will also be influenced by how much fuel you manage to squeeze in after the pump clicks off, and the indicated volume of fuel dispersed by the pump being accurate. In the UK, pumps should be checked and tested regularly for accuracy, although I dare say they’re not all 100% accurate.
 

FloridaNative

Passed Driver's Ed
Location
Central Virginia
I have hand calculated my mileage since day 1 (20k miles) on my 2017 GTI. The computer in mine is off by 2-3 mpg. Around 2 mpg (6%) on mostly highway tanks and around 3 mpg (10%) on mostly commuting tanks.

-Mike

Sent from my SM-G950U using Tapatalk
 

Strange Mud

Autocross Champion
Location
Small Town CT
Car(s)
Assorted
mine was about about 2-3 MPG off. I adjusted it through OBD11 107 was the number I used. Doing math over my last extended go around it was within .1-.2 mpg off. The OCD in me is happy. I know it really doesn't affect consumption but another excuse to spend the $70. My justification was turning on the factory alarm. All the other stuff is just frosting.
 

20ls01

Go Kart Newbie
Location
Texas
Car(s)
GTI 2016
Its really weird. Most tanks, the computer reads 2-3 mpg higher but its been spot on sometimes.
 

geokilla

Go Kart Champion
Location
Toronto, Ontario, Canada
Car(s)
2018 VW GTI DSG
How do you adjust it using OBDeleven?
 

southpawboston

Drag Racing Champion
Location
Somerville, MA
Agree, it will only give an indication of fuel consumption.

Calculating the fuel consumption manually over the long term will be more accurate, but this method will also be influenced by how much fuel you manage to squeeze in after the pump clicks off, and the indicated volume of fuel dispersed by the pump being accurate. In the UK, pumps should be checked and tested regularly for accuracy, although I dare say they’re not all 100% accurate.

In the US the fuel pumps never trickle more than a few drops after they switch off. They also have to be calibrated and certified at least once a year, IIRC.
 

imthanick_a

Autocross Champion
Location
Ohio
Not this thread again
 

Wrath And Tears

Go Kart Champion
Location
Azusa, CA
Car(s)
17 Sport, 99 E36
Not this thread again

Mine is 100% accurate because I've never hand calculated to see how off it is, so there! Take that you hand calculators. :)

Edit: alright you peer pressured me into it. Hand calculation from last tank is about 2 MPG lower so figure 8-10% off. Seems about right.
 
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