matador440

Just bought a 97 A8 as a project car. Looking forward to working through a bunch of projects on the car that are documented on AudiPages!

On the drive home from buying the car (700 miles) I was testing the trip computer's 'average MPG' to actual and it was about 6 MPG off. The trip computer said 29 MPG was the average, but the actual was closer to 23.

Is this a consistent discrepancy for the vintage A8's? If so... I'll leave it alone. If not... is this an indicator of any particular fuel/injection/intake/exhaust problems?

Any insight is appreciated!

Adjuster

I've noticed mine is not very accurate either, but not that far off.

I'm not sure you can change this very easy, even with a RossTech tool/VAG Comm device.

My tires are slightly larger than stock, so the engine is going slightly slower than the OEM wheels/tires.

In theory, this should result in slightly higher fuel economy, and lower performace, as it in the real world, changes the gear ratio for the final drive.

But, the stock wheels and tires are off in that the real speed is lower than indicated, and now with these wheels and tires, the real speed is nearly exactly correct. (IT's about one mph off at 82mph per the GPS, now just over 80mph is really just over 80mph... Good deal, while with the snow tires, and stock wheels/sizes the GPS says I'm going 78mph when it's indicating 80mph.. so to go 82mph on cruise control, I'm pushing 85 indicated or slightly more.. IE: The engine is turning faster than it needs to be with the larger summer wheels/tires.)

There is an easy test.

Use the GPS feature on your phone, or any nav system other than the stock one that does not have this feature that I know of. (The indicated GPS speed is usually pretty dang accurate, especially at highway speeds, and I trust it to within 1mph +/- of what the actual speed of the vehicle is.)

There are tons of free app's for the iPhone or Droid systems.. I like Speedview, it's got a cool HUD screen that "projects" the speed in large format backwards, so you can read it off the reflection from your windshield, so at night or in low light, you can see your speed in real time, on your "Heads Up Display" reflected off the inside of your glass.

I use it to set/check speeds on my cars, and of course when I used to travel, the rental cars are always all over the place, and since I tend to drive right up near ticket limits, I want to know if I'm going 82mph or 84mph.. As it might just be the difference between nothing, and a ticket.

And if you have to drive from SLC to Cheyenne, you really want to get every last MPH you can possibly get from the vehicle without a ticket.

Adjuster

PS: Where in Idaho are you located?

silverd2

No problem indicated. NO year A8/S8 reads the correct MPG's...always reads optimistically high...one of Audi's little white lies, like your coolant temp idiot gauge which says it's always dead steady at 90C (actually reads that way at 81-100C).

matador440

Thanks all for the replies.

Adjuster - I'm in Idaho Falls. I feel sorry for anyone who has to consistently drive through WY!