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MPG on the DIS

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by Marko, Jan 23, 2006.

  1. Marko
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    Marko Member

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    Hi

    I decided to check the accuracy of the average fuel consumption for a tank. The DIS said 52mpg and my calculations (taken from mileage completed on a full tank against the number of litres to re-fill) were 46mpg. I was slightly alarmed to see such a difference. 1 or 2 I would accept but 6! /ubbthreads/images/graemlins/confused.gif

    Has anybody else tried this? IS my method a proven way of calculating average mpg? Seems ok to me.

    Cheers

    Marko
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  2. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Neither method is exactly scientific so there's bound to be a discrepancy.
    What's a full tank? Even if you use the exact same pump at the same petrol station you'll still get a difference on when it clicks off. The only way to know for sure if the tank is full is to fill it until it overflows, which isn't ideal.

    I would expect a 10% difference anyway so your 11.5% is pretty close
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  3. imported_bubstar
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    imported_bubstar Guest

    [ QUOTE ]
    I would expect a 10% difference anyway so your 11.5% is pretty close

    [/ QUOTE ]

    Got agree with Andy there, 10% is generally regarded as the 'over read' of most trip computers..

    BUB /ubbthreads/images/graemlins/smirk.gif
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  4. mickey_a6
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    mickey_a6 Member

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    I reckon the inaccuracy in the DIS reading is far greater than variation in actually filling the fuel into your tank. I'd estimate it should be possible to have no more than 2 litres of difference due to click-off variation between fills (assuming using the same pump, calibrated accurately, at the same filling station). Even if you overflow it, you will probably lose up to a litre.

    On a 70 litre tank, the most I have ever put in is 64 litres - 2 litres of that 64 is 3.125% of the fill. It certainly is not going to be as much as 6.4 litres - 10% of the fill. As you point out, all the talk on DIS vs fill seem to confirm at least a 10% (over-read) discrepancy.

    Just my 21.7ml's worth (at 92p a litre) /ubbthreads/images/graemlins/grin.gif
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  5. Merlot
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    Merlot Member

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    I brim my tank all the time (the tank is too small for S4's) so there is consistency in comparison. I found the DIS on my 03 S4 Avant to be very accurate but the DIS on my old 04 S4 Avant and current 05 S4 Cab both over-read MPG by about 7%; ie I was getting about 1.5 worse mpg than the DIS suggested.
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  6. Marko
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    Marko Member

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    I rather thought it would be the DIS that is over reading. There is no guarenteed accuracy of MPG with these methods. I would have thought that the DIS could be made to much more accurate, particularly in light of what is monitored in the engines. I guess the costs of such accuracy would not be viable.
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  7. Merlot
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    Merlot Member

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    I think its got nothing to do with cost. Its all about making cars appear more economical than they really are.
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  8. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    I would imagine the DIS reading is accurate at say a consistent 56mph, but then becomes inaccurate above and below that speed. No idea why, but would seem logical, you can probably get to overead and under read depending on the style of driving.
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  9. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    What I'd like to see is an option to input the price you paid for the fuel so that the DIS could show you in pence per mile, that would certainly focus the mind on driving less aggressively
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  10. dstech
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    dstech Member

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    If your DIS is inaccurate you can adjust it.

    Use Vag-com or ask the dealer to adjust it for you.

    Module 17 - Instruments
    Adaptation Channel 03

    Adjust channel 03 to a higher number. It has a valid range of 85-115. The higher the number the lower the MPG calculation will be.
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  11. scoTTy
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    scoTTy Active Member

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    I'm not sure if I want to see the real lower mpg or not. /ubbthreads/images/graemlins/crazy.gif
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  12. markneal
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    markneal New Member

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    I agree, the DIS is low enough already, however, you would have thought in this day and age with all this tech, that it would be accurate to within a 10th of a litre. I had an Audi V8 (D1) once, that was accurate to the mile.
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