I might just be ignorant, but I brought my 8 to the dealership because the check engine light came on. The dealer couldn't figure out why it came on, but hours later said they fixed it. I asked how, and they said they reflashed the ecu and it fixed the engine light. I've driven two tank fulls now and getting about 20 miles less per tank than I was getting previously. I was getting about 230 miles per a tank (which isn't bad), but now i'm getting about 210. Any words of wisdom? Thanks.

 

Go back and ask them which flash you got. I recently go the "M" flash and my gas mileage went up. Noticeably
Call them up

 

Yeah - a "tank" is not a unit of measure, unless you're running it bone dry empty and pulling to a halt on the side of the road every time . Just calculate your mileage - reset the trip odo when you fill, then next time you fill take the trip odo reading, divide by gallons, voila you get miles per gallon, a real calculation based on standard repeatable units. Unless you calculating the actual mileage, you really can't tell with any certainty whether your fuel consumption has increased or decreased.

Regards,
Gordon

 

Yeah, what Gordon said. I noticed that the fuel gauge acted differently after the M flash - so don't go by what the gauge used to read before the flash. Calculate the mpg the right way. You'll probably find that the mileage hasn't changed, or has slightly improved (which is what I found).

 

There's an entire thread on the gas guage changing behavior after the flash.

Mine no longer ever reads at the 50% mark. While driving on a long trip it actually jumps straight from a notch above halfway to a notch below.

 

I have the "M" flash and so far I am getting worse mileage. Through three tanks I am down from around 17 mpg to 15.5. Weird.

 

yeah since m i've dropped from 17ish to 16ish mpg

 

i'm getting pretty bad milege.... bet 16 to 18 Litres per 100km.. dunno the exact conversion to mpg, but it's pretty bad

 

Another thing to consider is that to prove the M flash was successful, they tap the brake 20 times in 8 seconds (or so) and then the oil gauge sweeps.

This also resets what the ECU has learned and your car is like new again; my first two tanks after the M flash were not so great either, then it improved by 2 mpg.

Note that I'm not sure about this ECU resetting; I've never figured out what and how the ECU learns anyway.

-Peter

 

IT's pretty common for many cars to get worse gas mileage after you reset the ECU and it can take several days for the ECU to relearn everything and get back to it's old ways. At least this is what I've heard from various car owners, I've never experienced it myself since I don't even monitor my gas mileage.

 

My mileage went up from 16.3-16.9 to 18.3 to 18.9 in the same every day mileage. I just set my trip mileage button when I gas up and divide by the gal. It may take a while for your car to adjust, although mine was immediate on the first tank.