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Trip Computer Accuracy


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#1 EzzyRallyBoy

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Posted 17 July 2009 - 02:43 PM

1.6 petrol engine with first full tank of unleaded since new

Computer says 45.2 mpg - just re-filled now

315.8 miles travelled using 34.84 litres

34.84 litres / 4.546 (conversion to gallons) = 7.664 gallons

315.8 miles / 7.664 gallons = 41.2 mpg

So computer has been programmed to lie by 4mpg ??? :blink:

Or are the petrol pumps lying saying we have filled more juice and hence more profit for the garages, how often are the Government Weights and Measure guys checking at the petrol stations ??

If my computer is correct then I only filled up with 31.76 litres not 34.84 so thats a difference of 3.08 litres and at a 1 a litre that would be 3 more profit for the garages per person per tank !!!!!! :angry:

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#2 Trav

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Posted 17 July 2009 - 02:50 PM

1.6 petrol engine with first full tank of unleaded since new

Computer says 45.2 mpg - just re-filled now

315.8 miles travelled using 34.84 litres

34.84 litres / 4.546 (conversion to gallons) = 7.664 gallons

315.8 miles / 7.664 gallons = 41.2 mpg

So computer has been programmed to lie by 4mpg ??? :blink:

Or are the petrol pumps lying saying we have filled more juice and hence more profit for the garages, how often are the Government Weights and Measure guys checking at the petrol stations ??

If my computer is correct then I only filled up with 31.76 litres not 34.84 so thats a difference of 3.08 litres and at a 1 a litre that would be 3 more profit for the garages per person per tank !!!!!! :angry:


Did you reset your trip computer when you filled up with Petrol? As your trip computer will show you an average fuel economy not the exact fuel economy. If you hadn't reset it then it wont display the exact fuel economy for that trip.

Personally I think the Petrol Stations are money grabbing B***ards and I would say that they are the ones that are conning us out of fuel. :angry:

#3 EzzyRallyBoy

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Posted 17 July 2009 - 02:59 PM

Yeah zero'd the trip and average mpg when I filled it up at the nearest petrol station after I picked it up, and have done so again and will report back after another 300-odd miles - ta

#4 Trav

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Posted 17 July 2009 - 03:01 PM

Maybe try a different Petrol Station next time you fill it up and see if that makes any difference.

#5 DanGull

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Posted 17 July 2009 - 03:03 PM

Your sample isn't big enough - for one you can't be sure that you've used 34.84 litres as you can't be sure the tank was at the same level it is now when you started this set of readings.

Watch the gauges/figures for a couple of trips and see the results. You'll then have a set of figures and will be able to more accurately calculate the error (and there will be some) in your trip computer and/or the gauges of the petrol pump you use (I always use the same one personally for exactly this reason...)

For what it's worth, considering the number of petrol stations in this country, the gauges are regulated fairly thoroughly.

#6 TonyEssex

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Posted 17 July 2009 - 06:25 PM

isnt the trip computer just the average mpg you are achieving? so you cant use one figure to calculate the total distance covered

#7 harweyko

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Posted 17 July 2009 - 06:46 PM

I`ve not resetted my trip computer for last 5000km and also average fuel calculation, now it is showing 6.1 l/100km but according to my calculations I have average fuel consumption 7.03 l/100km (you can check HERE, really very good site) so I think that fuel computer is there just for your orientation, not for exact measurements...

#8 EzzyRallyBoy

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Posted 17 July 2009 - 08:12 PM

isnt the trip computer just the average mpg you are achieving? so you cant use one figure to calculate the total distance covered

You can flip through average mpg, miles covered since last reset, miles until tank empty and total mileage of car but clicking the left stalk and going through the options

When on a particular option if you press and hold in the stalk you can reset the counter

#9 greenymk7

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Posted 17 July 2009 - 11:04 PM

did u convert into yank gallons or english gallons?

#10 irononreverse

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Posted 17 July 2009 - 11:27 PM

did u convert into yank gallons or english gallons?


:blink: They have different gallons??

#11 RIIIDAA

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Posted 17 July 2009 - 11:57 PM

:blink: They have different gallons??


Yes

http://www.convert-m.../convert/volume

They also have 'dry gallons' which differ again

#12 DanGull

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Posted 18 July 2009 - 08:30 AM

The maths that's been used has converted things into imperial gallons, which is what are used for MPG calculations in car brochures and the like. If you convert everything into US wet gallons the fuel economy gets even further away from the trip computer's findings.

Tony - your post confuses me. It's an average reading, so if you know the period it's measured over in terms of distance you can work out your exact fuel economy from it. That's how an average works.

#13 EzzyRallyBoy

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Posted 05 August 2009 - 06:59 PM

Just filled up the tank for the second time at a different petrol station to the first time (no drops !!!!) and :-

Computer said 45.5 mpg - 290.0 miles travelled using 34.94 litres / 4.546 (conversion to gallons) = 7.47 gallons
290.0 miles / 7.47 gallons = 38.8 mpg - Trip computer over-excited by 6.7mpg !!!!!!!!! - Well not happy trip is way out

First fill up computer said 45.2 mpg - 315.8 miles travelled using 34.84 litres / 4.546 (conversion to gallons) = 7.66 gallons
315.8 miles / 7.66 gallons = 41.2 mpg - Trip computer over-excited by 4.0mpg

Don't trust the trip computer .........................

#14 darude

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Posted 08 August 2009 - 09:44 AM

My example was posted here:
http://www.fordowner...x...ost&p=34453

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