themorn2112

Greetings,
I am enthralled with my 2005 A6, but have an issue I hope to get insight on. When I purchased my A6 I was seeing about 11 MPG. My last 2 fill ups I been seeing a little over 8.5 MPG of premium fuel only. this is poor even by Luxo V8 standards. I have been tracking the fuel economy with an app I installed on my phone, so I have a steady fuel economy track record. I live in Chicago. I am not a lead footed driver. I doubt that a winter blend of gas would cause such a poor fuel economy showing. My drive has been almost exclusively local/city driving. Are there any issues or quirks specific to 4.2L V8 Audi's that is a major factor for the poor fuel economy? I expected a less than stellar fuel economy, but the poor fuel economy is exceeding my expectations. Any helpful insight, views, and suggestions will be deeply appreciated.

raj99

when was the last time you changed the fuel filter?

newa6er

first, i wouldnt trust the phone app, second, i wouldnt trust the car computer

fill it up and reset the trip odometer

drive it til near empty, fill it up again and divide the number miles on the trip odometer by the gallons you just filled

J. Patterson

City driving is REALLY variable but it is hard to imagine getting 10 mpg or less no matter what. Check your true mileage by calculation and compare with the display. Then take the car out for a highway run and see what it gets at 70 mph level ground for a few miles. Our 3.2 gets 29 mpg at 70 mph. I would expect a properly running 4.2 to get at least 24 mpg under same conditions. If your car proves to be REALLY getting 10 mpg in town and significantly less than it should on highway, the first things to check are the O2 sensors and or the MAF. A vag scan of block 32 will tell you a lot about fuel mixture correction. https://www.audiworld.com/forums/sho....php?t=2580765

Other items that can negatively impact fuel mileage are the thermostat, the temp sender, and the intake air temp sender.
Carbon fouling of the intake and intake valves can occur on Direct injection cars but I don't think you 2005 4.2 is direct injection.

Good luck! I have been down this road with the TT but the A6 has always been very frugal with fuel.

A6Gary

Are you calculating the MPG by recording the gallons to fillup, and using the trip mileage indicator to record the miles driven for the gallons consumed? If not, you're not getting an accurate measure of the actual fuel economy. Your phone app is not sufficiently accurate to record the miles driven. If your MPGs are that low, you may need new plugs and possibly an air filter. And the winter mix will give you a lower MPG by about 1 – 2 MPGs compare to the summer mix.

2.7allroader

I agree with those who posted above. You should check your consumption based on actual mileage and actual gallons used. How many miles do you have on your car?

Also, I do not think it is either the air or fuel filters that could be wrong with it. It is definitely something that has to do with the part of the fuel injection system that calculates the air/fuel mixture (either the MAF or the O2 sensors). You should get it checked as the car is running a rich mixture and this situation normally takes out the catalytic converters.

Just my $0.02.

SchwarzS6

I would suspect that if the mileage were that poor because the engine was running rich or the O2 sensor(s) were messed up you would have a check engine light. Also, if you are really running rich the cats will burn off the excess and run very hot, you would also get a sulfer (rotten egg) smell from the exhaust.

slowguy

Agreed, manual calculation. Agreed, too rich and you should see a CEL. If you have vag-com, it should definitely be scanned for codes and issues that don't trip the CEL. Could be many problems from dirty or stuck injector(s), dirty air filter, weak spark, malfunctioning maf, to name just a few. Although, most of these problems would detected by the computer and shown with vagcom. Also, you should notice a decrease in performance.

Depending where your at, I can probably meet up with you and scan your car if you don't have one. I routinely work north of the city and occasionally work downtown (although I am very short on time when working downtown).

EDIT...I get anywhere from about 16-17 city up to 26 on the highway with a 2.7t turned up to over 300hp. I would think you should get at least 14-15 or better in the city with easy stop and go.

themorn2112

Thank you for your response.
I Purchased the car 6 Months ago from a major dealer here in the Chicago suburbs. The fuel filter is something I will definitely look into.

follow up: I drove the car on a stretch of hi-way, then filled it up again. My fuel economy fared better with an mpg rate of 14.24, comprised of slow and go hi-way driving. This puts a damper on the fuel filter as being a possible problem, but I will strongly consider this.

themorn2112

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Thank you for your response,
I don't use the car's computer for my calculations, as I fully understand the inaccuracies inherent in most car computers. I mainly use the car's computer values as a quick and relative "on the spot" indicator.
I trust this android app (fuel log), as all this app does is calculate the values I enter into the app (Odometer, fuel amount, and price). The app does the math and stores the results. "Fuel Log" is basically a purpose driven calculator that stores my results. the advantage is that I can track my A6's fuel economy trends. I trust and verified the results from this app. I am a former electronics technician, so I am very familiar with the math involved in regards to calculations and conversions. I also zero out my trip odometer with every fill up out of habit to cross reference the apps calculations with my own.
I generally keep my tank filled with Shell premium gas. The price for a fill up from empty is brutally expensive using premium gas (roughly USD100.00), so I refuel when I use a quarter tank of fuel. My A6 is a daily driver, but I don't drive often.