Kolshak

My Avg MPH & MPGs are almost always stuck @ 30 & 14 respectively.
Does anyone know how often or over what period of time the OBC recalculates these numbers and if is their a manual reset?
I almost feel like taking a nice liesurely road trip to see if I can get into the 20 mpg range.

Chuck Jones

Kolshak: There's a manual reset on your lower left "stalk" below your turn signal stalk. It has four positions and you down or up click to move thru the different functions. You reset by pulling the stalk towards you and holding it till the function zeros out. One of the functions resets your mpg...and it will have an "mpg" designator on it. There is also one for average mph, miles left before you run out of gas, outside temp etc. If all else fails....read your owner's manual....it has a wealth of info in there. I reset mine every time I fill up and, depending upon whether I've been running in traffic or on the freeway, (also affected by how much you stomp on it) I usually get between 18 and 26.

Kolshak

Thanks Chuck - we'll give that a try.

auto-xr

26 mpg going to the track.
10 mpg at the track.
running 235/295 PS2s

rountreed

14MPG sound about right for average Autobahn at around 140MPH, other than that seems low....maybe a computer air-fuel mixture problem? I would send Loren an email over at renntech.

BruceP

Just the opposite experience, here. I find the car gets stunning mileage at speed, and terrible mileage in urban driving. Honestly, I went more than 50% further on a tank over during my last extended 15-160kph run than I do in daily driving in the city.

It's inefficient at low speeds. Built that way, like "a race motor" (quoting Excellence, here). Add the fun-killing adaptive DME into city driving, and it should be no surprise at all that it's a pig around town.

rountreed

Bruce would agree at 150-160KPH but I said 140MPH which is approx 227KPH.

NNH

I saw 17mpg for 120mph average at the last Silver State. I'll report back next month on the mileage for 135mph.
I get 18mpg going to work over Topanga, 25+ on a decent run on the freeway, and I got about 9mpg at Buttonwillow on Saturday. 14mpg sounds low, but not impossibly low.

BruceP

225.3, actually.

Obviously, beyond a certain point, mileage will decline at extreme speeds, what with HP rising with the square of speed. My argument is simply that, within the typical driver's operating parameters, this car will get far better mileage at highway speeds than at urban speeds, and my further personal observation is that the delta is unusually large with this car. Just trying to reassure the original poster that his car is fine.

Gretch

Very reliable, 'cept for the time it upchucked a tranny....... other than tires, pads and oil, that tranny is the only money I have ever spent on the car (besides mods)..... input shaft bearing **** the bed.

I drove my 928 100,000 miles also...... still have it, semi retired now.

rountreed

Well said Bruce! I too think he is ok but man throwing in the square root etc... always reminds me of a check ride, yuk! Oh and sorry I was off 1.7MPH I just did the quick math in my head.

Kolshak

I appreciate the input and agree with your point, however I think I should be getting slightly better MPG. I reset my OBC's average MPG calculation and took a relatively short HWY drive @ ~ 60 to 80 MPH in 6th gear - I could only get a max average of 18 MPG. Even though it was a short trip, wouldn't 18 be my max attainable MPG (under those circumstances), or would it take a longer trip to determine the max fuel efficency?

jasper

17.7 mpg on my daily commute, 70% street, 30% highway. I read it as 13.3 litres per 100 km though.

BruceP

You need a longer drive to move that number.

Also, the only way to really accurately calculate mileage is to fill the car up, drive it until most of the tank is gone, then fill it up again. But I really do think you're okay. As I said earlier, I've never seen a car with a bigger delta between city and highway mileage. I've also never seen a car with such a responsive adaptive DME function, which I think partly explains this. This is subjective, but it comes from a bit of experience: If I take my car out on the highway for an hour or so after a couple of weeks of urban commuting, the transformation is bigger than I've had 'chipping' other cars. It sounds different, throttle response is sharper, and so on. I've never had a car that liked an Italian tune-up so much. I'm only guessing, but I think the inherent inefficiency of this engine at low speeds combined with the engine controls' aggressive adaptation to driving style is almost inevitably going to give you dismal city mileage.

YMMV, so to speak. All disclaimers about subjective observation, etc...

krisd

I got 25mpg on a 2000 mile freeway trip average speed 78mph. My normal commute is on a two lane mountain road with many sharp turns, I rarely get above 15mpg there. If at least half your commute is on the freeway I would expect your mileage to be closer to 17-18 mpg.