Fuel Computer Problem?

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Mar 3, 2005 | 04:52 PM

fliegerace

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Fuel Computer Problem?

If you fill your tank (18 gal) and are averaging 15 mpg, the "range" display should show 15 x 18 = 270 miles. If you then jump on the highway, reset "average mpg" and now get 25 mpg, shouldn't the range be 25 x 18 = 450 miles? That's the way it worked on my C5 - it was very accurate and I relied on it a lot. The most range I show on the C6 (on the highway) with a full tank is about 317 miles. It seems to be (possibly) increasing very slowly, as if its going all the way back to the first mile driven and ignoring the reset of the average mpg. I'm only on my 2nd tank (275 miles total), but I wonder if anyone else has noticed this - or do I have a unique problem?

Mar 3, 2005 | 05:47 PM

Asterism

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i doubt the computer calculates the range by simply multiplying
the current DIC average with the remaining fuel volume. if it did, youd
get a completely insane range value if you reset your DIC average
while coasting downhill on the highway with your foot off the gas.

if you coast downhill youll see your "instant" value go as high
as 99mpg. if you reset the average value during the coast and
the computer used the new average value to calculate the range,
youd get 99mpg*18gal which is obviously bogus.
(assuming a full tank, and DIC average reset during coast)

in practice i think the computer uses a much longer average
when calculating the range that is completely unrelated to the
one displayed on the DIC which can be reset at any time.

Mar 3, 2005 | 10:09 PM

fliegerace

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Quote:

Originally Posted by Asterism

Your point is well taken, but the range value is meaningless on a highway trip if it is based on the urban mpg (or vice-versa). I never tried to get a range value on the C5 when coasting downhill, but I often reset the average after a few highway miles and got reliable range numbers. BTW, I notice that the C6 max, when coasting, is 70 mpg, not 99 as on the C5.

Thanks for the thought

Mar 3, 2005 | 10:18 PM

iblumberg

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From: San Carlos CA

Since I've only had my C6 for 2 weeks, I can't comment on how it might work, but I've had cars with similar range displays for several years. Each of them seem to do some sort of weighted running average for MPG for the calculation. Thus, if you have been driving around town for the last several tanks of gas and then jump on the freeway, the range does increase, but slowly over the course of an hour or so. This seems to make sense and generally does give an accurate range for longer trips after about the first 45-60 minutes on the freeway.

It seems like a good compromise since you don't want the predicition to get too optomistic if you exit the freeway after 1/2 hour.

Ira

Mar 3, 2005 | 10:41 PM

Another Yellow

Le Mans Master

Joined: Feb 2000

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From: Yorktown Heights NY

St. Jude '03-'04-'05-'06

In 3,804 miles I have filled up 21 times. At the time of fill-up the range has been 306 to 454 miles.

The 306 mile range the DIC said 16.2 mpg. Actual mpg was 15.99

The 454 mile range the DIC said 25.6 mpg and the actual mpg was 26.26

I can email you all 21 readings if you like.

Mar 3, 2005 | 11:19 PM

Gussy913

Burning Brakes

Joined: Nov 2004

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From: Staten Island NY

St. Jude Donor '05

Just my 2 cent's but I noticed this on my 04 Tahoe, The computer is always recalculating the fuel range. If I have 25 miles till empty and jump on the highway obviously your Avg will go up and you will get more than the 25 miles. Also if you leave your range meter on and clock the mile marker's ( which I have done ) you will notice when you hit a mile your range does not move until you move closer to the 2nd mile. I have not done this on my C6 yet but I'm sure it's the same...
Chris