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Fuel consumption

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Old Oct 29th, 2024, 19:05   #1
Mal58
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Default Fuel consumption

I use a display theme which shows average fuel consumption in the left hand lower display, I also cross check by resetting the trip every time I refuel and dividing miles by how many litres I put in.
I'm getting about a 12% discrepancy between the average fuel consumption and the miles/litres crosscheck, actual mpg is 12% lower.

This is on a low mileage V40 T3, anyone else having issues with fuel consumption not being reflected accurately?
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Old Oct 30th, 2024, 10:40   #2
RS3100
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As the speedometer over-reads on nearly all vehicles to comply with legislation, the figures shown in in-car displays are rarely accurate. A better method is to brim the tank on every refill, note the volume of fuel filled and mileage travelled. Over time this should give you a much more accurate indication.
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Old Oct 30th, 2024, 16:26   #3
Mal58
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I'm already brimming the tank, have been for years as I like to know if something is potentially wrong (Also, fuel is a significant cost and sorting out tuning issues normally pays for itself over time).

I previously had a 2.2D Mazda 6 which showed virtually identical average mpg to my brimming the tank calculations.
Average MPG is calculated using fuel supplied to the injectors which is extremely precise, the only other metric involved is mileage which is according to GPS is reading 3.33% over (Speedo shows 62 when GPS shows 60).

The 12% discrepancy is over 1800 miles and is fairly consistent per tank.
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Old Oct 30th, 2024, 18:18   #4
RS3100
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Quote:
Originally Posted by Mal58 View Post
Average MPG is calculated using fuel supplied to the injectors which is extremely precise, the only other metric involved is mileage which is according to GPS is reading 3.33% over (Speedo shows 62 when GPS shows 60).
What is your source for that information please? I'm not saying you're wrong, but according to VIDA no such parameter or data related to fuel supplied to the injectors is either generated by the ECM or supplied to the DIM, at least on VEA petrol engined cars.

The DIM receives distance travelled information from the BCM according to the number of wheel rotations counted and the programmed tyre circumference. The latter can differ substantially from the actual rolling circumference. On my car with 205/55R16 tyres the rolling circumference is factory programmed as 1935mm, whereas the actual rolling circumference of my tyres as measured varies from 1985mm for the OEM tyres to 2000mm for the all season tyres that I currently have on the car. Both sets of tyres are the same nominal size.

Fuel level and hence consumption is calculated by the DIM according to the tank sensor voltage, which varies according to the volume of fuel left in the tank.

Average fuel consumption is apparently calculated from the last trip counter reset according to calculated distance driven and calculated fuel consumption.

Last edited by RS3100; Oct 30th, 2024 at 18:21.
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