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B7 a4 2.0tdi 170... Massive mpg drop

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by Jonbooth, Sep 23, 2013.

  1. Jonbooth
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    Jonbooth New Member

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    [Sep 23, 2013]
    Morning AllBought the car in June and have regularly got 55 mpg doing my commute to work and back.Mid last week I noticed that the fuel remaining indicator in the car had dropped significantly from where it should be with the amount of fuel left in the tankA further 2 fill ups later and my mpg figures are 38 & 41 Mpg on the 2 tanksThe car is well serviced and although I've had a mass of problems with DPF removal, remapping, an egr cooler pipe, wheel bearings, drive shaft and having to replace both rear springs, the car has been running pretty well up to last week.The only significant change I can think of is outside air temp has fallen from the early to mid 20's to 14 & 15c... If the air intake temp sensor was faulty, would that cause the car to run rich and therefor cause this problem ? Has anyone got any other idea's ? Thanks in advance for any help you can give Car has 129k on it
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    [Sep 19, 2014]

  3. jdp1962
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    jdp1962 Grumpy Old Moderator Staff Member Moderator

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    [Sep 23, 2013]
    Outside temperature is significant, because of the time taken for the car to get up to running temperature from a cold start. How long is your commuting journey?
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  4. Jonbooth
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    Jonbooth New Member

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    [Sep 23, 2013]
    Hi JDP....Normally about 30-35 mins and around 27 miles. I wouldn't have thought it would have been cold enough to make such a big difference but I'm happy to be corrected :D .... Do u think that could be it ? Is it better to leave it to warm up before setting off ?
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  5. Brodster
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    Brodster Shark Performance In Scotland Regional Rep Site Sponsor VCDS Map User

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    [Sep 23, 2013]
    Look at the usual suspects such as failing DPF and clogging EGR valve. Both will give you the symptoms your experiencing. Take it for a spirited drive and keep in 4th gear with revs high for about 15-20 mins ensuring the engine temp is optimum. This will start a manual regen and hopefully blow all the **** out of the DPF system.
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  6. jdp1962
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    jdp1962 Grumpy Old Moderator Staff Member Moderator

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    [Sep 23, 2013]
    Definitely don't do that. The most efficient way to get an engine up to optimum operating temperature is by driving it (but gently of course). The drop in mpg you describe is probably too big to be explained solely by outside temperature reduction (especially over a 27 mile run). My commute is 11 miles, so it is more relevant.

    As Brodster says, check all the usual suspects.
    Last edited: Sep 23, 2013
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  7. Jonbooth
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    Jonbooth New Member

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    [Sep 23, 2013]
    Thanks for coming back to me... The DPF has been removed (which is why I needed a new egr cooler, they caught the pipe that drops from the cooler to the side of the block .... £300 .... Keeerrrrrching !!!) .... Are there any other symptoms that an egr valve might give... I'm getting a wining noise when I back of the throttle, my garage has said it's the veins (?) on the inlet manifold cause it's variable (sorry, haven't got the best knowledge of turbo's) Sounds a bit like Darth Vader's battle cruiser. Could that be the egr valve sticking and out if interest, would this cause an underboost fault ? Had an underboost fault when I first got the car in June but haven't seen anything of it since.
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  8. Jonbooth
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    Jonbooth New Member

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    [Oct 5, 2013]
    Just as a quick update to this, i removed and cleaned the Mass Air Sensor and reclipped the airbox back to the wing (clip had broken) and now its seems to be better... not as good as it was but now getting about 45mpg...

    What are the main things to check... from scouting round it appears to be the water temp sensor, the egr valve clean, the mass air sensor & the air intake manifold temp sensor. Is there anything else i should be looking at ?

    Thanks
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  9. jimbooboo
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    jimbooboo Member

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    [Oct 6, 2013]
    I'm experiancing the same, but with a 140bhp cabriolet. I think its my cam shaft though.. :/


    Do you hear a weird sort of blowback noise coming from the the intake?
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  10. joaopedr
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    joaopedr New Member

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    [Nov 19, 2013]
    Any update? I'm experiencing the same problem with a 2.0 TDI Cabrio with DFP removed.
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  11. DieselJake
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    DieselJake God Mode

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    [Nov 19, 2013]
    Weather or driving it like a BMW.
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  12. joaopedr
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    joaopedr New Member

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    [Nov 19, 2013]
    Even beeing very careful can't get bellow 9,2L/100Km in the city (urban driving).

    Its a 2.0 TDI convertible with automatic gearbox.
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