CEB

...is it my A6 or are all trip computers this screwy?

Aside from what the trip computer says, I generally get about 360 miles to a tank of 93 before the little pump picture comes on. Here, however is the odd part:

Let's assume I have driven 360 and the trip computer says 20 remaining (380 on tank)

When I gas up (usually same station, Tuesdays when 93 is cheaper than 91), I reset the trip odo to 0. The computer will show 350 miles to empty (it said 380 just before fill up)

Over the next 10 miles or so, the computer will drop slowly to about 320 remaining (ergo 330 to a tank) and then will increase over the next 100 miles or so to give me a total of 450 for a tank (right now it shows 345 remaining with a trip odo of 141 - 486 for a tank -- this morning it went as high as a 540 a tank). There after it will drop to give a combined total of about 340/350 until I have driven about 300 miles. At that time the computer will show about 110/120 remaining until it plummets to 40 (at about the 310 mile mark) and stays there until I get to about 350 - then a quick decline to 25 and then beep......

I figure it is just the nature of the beast - I do about 30 miles one way commute everyday (25hwy/5city) - no traffic in the morning - heavy-ish at night. Weekends are prolly 50 hwy, 30 city a day.

Oh, another off topic question - last night my car made a kind of whimpering noise (1/2 second) right before the beep when I locked it with the remote. It did it a couple more times as I un-locked/locked the car (on lock only). After about 4 times it sounded normal again. Any ideas - normal?

miamigrrl [midori]

and how much your engine has to work. It constantly recalculates a bunch of factors to come up with that number.

ummm... I think

ZCD2.7T

Yup. What she said. Mine goes thru the same changes/updates each tank. NBD

myfirstimport

It is pretty dead on near the end of a tank. When mine shows 0...I have about 3/4 of a gallon left

Quattrogirls_dad

I've had 4 Audi's with the trip computer; all have the same characteristic you're seeing as far as "miles to empty". Midori is right; the computer constantly recalculates the "miles to empty" based on the actual rate of gas flow and your speed. I just drove back from Woodland Park to Colo Springs on a nearly full tank; 15 miles and a drop of 2500 feet (downhill almost all the way) so I was coasting at 60 mph. "Miles to empty" read 860 miles!

Cornelius Scriptor

...until the end (zero). I think it uses input from current fuel consumption, as well as average rates from the earlier portion of the tank.

The major problem is a 'garbage in, garbage out' issue, I believe. One of the inputs must be the from the floating tank level sensor for the fuel gauge, which is not well corrected for the different shape of the tank as the level falls. I find on my S6 that the top and bottom quarters of the fuel gauge are more like thirds of the tank (in actual volume), as is the middle half.

I wish Audi did this better (only a Chrysler Cirrus I once had was worse). For comparison, our Volvo's 7o litre tank is marked in 10 litre increments on the gauge, and is always within 2-3 litres of actual volume.

TXurS6

There are many variables and some, if not all, are probably weighted with a constant. I figure there are variables for gallons remaining, current fuel consumption rate, driving style history (for this tank). There may be more for things like current vacuum and reserve volume. Throw all of these into a predictive algorithm and it's tough to get an accurate reading at any given point in a tank of gas.

mjt

The car runs richer on cold starts - all else being equal consumption will be slightly higher until the car is warmed up.

Additionally, the volume of fuel in the tank changes with temperature - morning vs. evening vs. just out of the underground storage tank...

phred

Why risk running the tank dry, messing up the ECUs etc. and getting air into the system? Plus there might be sediment/water near the bottom.

Fill up at 1/2 or 1/4 tank, just make it a habit.

phred

you're so busy analyzing your trip computer you're not paying attention to traffic! :-)