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DIS and actual MPG widly different..

Discussion in 'Diesel forum' started by westy_pj, Apr 30, 2007.

  1. westy_pj
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    westy_pj New Member

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    [Apr 30, 2007]
    Hi everyone,
    First post here, so be gentle (nice forum by the way).
    After many cars under the bridge (?) I've found my way to an A4 TDi sport, 04 PD130.
    It's great but.....the DIS is showing 57mpg and my full tank to full tank calcs work out to 44mpg.
    Any know why the big difference?
    Cheers.

    :icon_thumright:
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  3. Macduff
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    Macduff Member

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    [May 1, 2007]
    DIS is never accurate but 13mpg is way off. Mine is usually about 2 mpg out. Are you sure your calculation is correct? I do miles / litres * 4.546 to get mpg.

    Also, are you sure you are looking at the DIS 2 reading (not DIS 1 which is trip stats) and also did you reset the DIS mpg when you filled up the tank?
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  4. westy_pj
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    westy_pj New Member

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    [May 1, 2007]
    Yes, yes and yes.

    From last diesel recepit........57.67 litres with my trip showing 517miles.
    57.67/4.546 = 12.686 gallons.
    517 / 12.686 = 40.75 mpg
    DIS 2 is showing 57.2 mpg (reset at each fill up).

    Previous tank worked out a bit better to 44mpg, but still showing 57 ish mpg in the DIS 2.

    Err......:confused: :confused:
    #3
  5. coupe-se
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    coupe-se Member

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    [May 1, 2007]
    I have found the same with my A3 over the last 9 months.

    DIS readout 2 normally says 39-40mpg overall ............ when calculated from the actual fuel put, in it works out at 46mpg in reality.
    #4
  6. Teutonic_Tamer
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    Teutonic_Tamer GreasedMonkey HoofHearted

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    [May 1, 2007]
    The only definative way to check this, would be to phyisically brim the tank and re-set the trip odometer, and the trip computer 2, and then run the car until nearly empty. Brim the tank again, and check all your calculations.

    If you do notice a discrepancy between DIS and actual, the stealer, or VAG-COM, can tweak the settings for the DIS fuel consumption readout.
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  7. coupe-se
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    coupe-se Member

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    [May 1, 2007]

    Eh???:think:

    If the I reset the DIS when I fill up; which I always do; surely whenever I look at the DIS average MPG on readout 2 it will always display the overall mpg UP TO that point?

    Thus if I fill up at half a tank the DIS will show the average mpg over that half of the tank!!

    Cannot see how brimming a tank alters the mpg reading on the DIS?:think:
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  8. westy_pj
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    westy_pj New Member

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    [May 1, 2007]
    I have VAG-COM....could you point me to a "how to" on this, please.

    Thanks.
    #7
  9. Teutonic_Tamer
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    Teutonic_Tamer GreasedMonkey HoofHearted

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    [May 2, 2007]
    OK, two issues here.

    Because you are comparing an average (the DIS reading), against an absolute (the actual volume of fuel you squirt into your tank) - you need to a/ understand averages, and b/ realise differences in petrol station pumps.

    The average first. An average, by its very nature, improves in accuracy with more data. So, a relatively short run, of say less than half a tank full, could lead to errors in the calculation of the average. The longer the run, the more data is captured and calculated, the more accurate the average will be!

    Now, the actual volume of fuel. Different fuel stations can have the pump "cut-off" set at different levels, some even pump at different delivery rates. Then there is the environmental issues (hot vs cold ambient temps) which can affect how full the tank is filled, using the cut-off. Unless you can guarantee that you use the identical pump, on the same filling station, at identical ambient temps, then there will be a discrepancy in the actual fuel volume you replenish in the tank. This discrepancy won't affect the DIS readout, but it will affect the "true" volume of fuel used!

    You could even leave DIS2 without a reset for 3 or 4 tankfuls, and providing you brimmed it on the intial re-set, and then again on the final reset (and you keep your fuel receipts) - you should have a very stable and accurate average in your DIS.

    HTH, rgds
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  10. Teutonic_Tamer
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    Teutonic_Tamer GreasedMonkey HoofHearted

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    [May 2, 2007]
    Sorry, I don't have VAG-COM.

    The main Audi stealer (and previous Vauxhall stealer!!) did confirm you can specifically alter the settings for inaccurate DIS readouts.

    I also found it somewhere on another forum, maybe AudiWorld.com, whereby they posted the actual module and "how-to". Is there a VAG-COM board on this site? If not, have a rummage in AudiWorld, or Vortex.

    Rgds
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  11. westy_pj
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    westy_pj New Member

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    [May 2, 2007]
    Thanks for the info, I have found the adaptation channel in VAG-COM (Audi World by the way!)
    You can only adjust it +/- 15 % though and mine appears to be 23% optimistic.
    Oh well, I'll give it a go.
    Still not too chuffed about getting low 40's to the gallon though!:(
    Cheers,

    :icon_thumright:
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  12. Teutonic_Tamer
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    Teutonic_Tamer GreasedMonkey HoofHearted

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    [May 2, 2007]
    OK, cool. Its always good when someone comes back with a positive reply - at least I'm not talking out of where the sun don't shine! :o.k:

    Don't suppose you can post the link for AudiWorld, or the full module access details.

    Hmmm, are you running on OE tyres, with good tread depth, and at the correct pressure??? If you have swapped to a different tyre/wheel size, there is also an adaptation for that too - and that could also affect your DIS readout!

    Keep us informed of your progress.

    Get some lighter shoes! :p
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  13. westy_pj
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    westy_pj New Member

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    [May 2, 2007]
    Car is totally stock, tyres are at 34psi all round and have approx 2.5mm tread all round. Service is due in 2,000 miles, perhaps this will help.

    Here is the link.

    http://forums.audiworld.com/a4gen2/msgs/1009862.phtml

    Will try when I get home tonight and post up what happens.

    ..and I've never had light shoes, ask the local Constabulary....:busted_cop:

    :icon_thumright:
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  14. westy_pj
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    westy_pj New Member

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    [May 4, 2007]
    OK, I've changed the value in VAG COM to 115 which, not surprisingly, immediately knocked 15% off my DIS 2 reading - making it 49mpg.
    I'm going to run for at least 300 miles now and fill up again to see what's happening this time!! :think:
    This will take me about a week.


    Could any dodgy sensors cause this.. MAF or fuel temperature sensor?

    :icon_thumright:
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  15. meatychi
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    meatychi Member

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    [May 4, 2007]
    It could be the consistency of the fuel you are using.

    I have xperimented with SVO and it effects the DIS mpg readings because the consistency is slightly thicker but the overall mielage is not affected.
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  16. westy_pj
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    westy_pj New Member

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    [May 10, 2007]
    Well, the plot thickens...
    (I've posted this in another thread in answer to another query, but updated this as well)
    "Basically had the car for 6 weeks.
    Impressed by performance but not fuel economy, DIS reading way different.
    Then I get a warning light, have it scanned and it's a 'Fuel temperature sensor' error. Get it cleared and carry on.
    Then buy VAG-COM 'cause there's other things I want to check and modify.
    Decide to check fuel temperature reading - cold overnight engine - reading 126 degrees!!
    Obviously duff, says I and order a new one.
    Fit new tonight and check reading.....still 126 degrees...oh bugger....but hang on a minute...what was that black box connected to the sensor...not had a diesel before so thought it was supposed to be there..
    Lightbulb moment....it was a tuning box that I was not told about when I bought the car!!
    Removed offending article and checked reading....36 degrees (engine still warm from drive home)"

    So now I've got to fill the tank and check it out again!
    Cheers.
    :icon_thumright:
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  17. Teutonic_Tamer
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    Teutonic_Tamer GreasedMonkey HoofHearted

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    [Jul 3, 2007]
    Westy, do you have any updates for us on this issue?
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  18. westy_pj
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    westy_pj New Member

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    [Jul 5, 2007]
    Sure, since removing the offending article, I managed to 'trim' the DIS reading to within a couple of mpg of the DIS.
    I think the value is now set to 105, via VAGcom and I'm getting approx. 47mpg tank to tank.

    Runs a bit smooooother too.

    Cheers,
    :icon_thumright:
    Westy.
    #17
  19. JGrant1285
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    JGrant1285 Sir Scouser Benitez

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    [Jul 9, 2007]
    I have a 52 plate B6 A4 1.9TDI. I fancy getting VAG-COM, but i have no idea what version of software,nor what cable to order!!! I need a cable with a USB connection (for my laptop). Can anybody help me at all?

    many many thanks in advance too!!!
    #18

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