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Discussion Starter #1
well i have my g6 for one full week and with 330 miles on the clock i have gone through a tank and a half and i think this is a little odd that a new efficent car is getting the gas miles of my dads trailblazer ss. ive been back to my dealer and he said its odd, but yet my dad who was a gm service man for 25 yrs n the 80s did sugest that maybe the computer has a break in cycle that runs the car a bit rich on break in, has anyone heard of this, and has any one who has their computer reflashed get better gas miles, i have the black soot on the tail pipes which shows its a bit rich anyone else with the bad gas have these symptoms
 

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Discussion Starter #3
for the most part im baseing it on the dic i have gone through 24 gallons in 340 miles, the dic is pretty accurate in what it says i got about 260 miles on my first tank, now im babying the car and it looks that ill get about the same if not a touch better, what gives, wheres the 28mpg on the highway??!!
 

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I had a chance to drive one with an auto trans for a while. I drive mixed city/highway but never any long highway trips. I think I averaged about 18-19 MPG but have a little heavy foot.

I think I got 20-22 with my 2005 GT. My wife gets around 25-26 MPG with same vehicle and she does more stop/go driving :)

So yours does sound a little low but give it a few more tankfuls.
 

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I have a GTP with the 6 MT. On the highway using 6th gear(when up to highway speed), I receive 26-28 mpg with a peak of 30 mpg, at times. :)
 

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I posted on another similar thread, raise your tire pressure a couple pounds over what the sticker on the door says... One thing I'm noticing of the people experiencing lower gas mileage is that they have the 3900 engine models. High performance = lower mileage. Another poster listed not to let the car sit and idle, that also kills mileage more than you would imagine, and keep your foot out of it, accelerate smoothly and slowly to the posted speed limit.
 

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Discussion Starter #9
i got my tires up to 35psi andi drive like an old lady its going back to the dealer in a week for a ding in the bumper from the showroom and the warped rotors, im gonna have them flash the computer cause i sometimes have the hard start when the car is warm, only happened a small hand full of times but i dunno maybe its just got a glitch it happens i build cars i know nothing is perfect even from the factory thats y im not pissed or even bothered its my first new car and ill eat, shit and die GM ill never own anything else but tru american from the GENERAL!!
 

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I went back and looked at your original post, just to give you a frame of reference, I didn't start getting mileage like I thought I should until I got around 3000 miles on the car. I have a 3500 engine and getting around 24.5 town and very short drives and get 30-31 on a trip, I'm happy with that. Originally around town I only got 19.
 

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Discussion Starter #11
my first tank average was 11.5 im close to 17 with this tank but with grandma behind the wheel i love the car the only thing bringing me down is the gas miles hope that will change soon
 

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Silver 2006 G6 GTP Coupe
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g6zeek said:
3.9 gtp coupe
I drove a few different GTPs before purchase. First one had 25 or so miles on it and ran REALLY REALLY well. Second one had 5 miles and a stone-dead battery, and after jump starting it ran really poorly (performance-wise) - but was getting better near the end of the test drive.

ECUs in cars have had the ability to learn how to tailor themselves to run correctly (to some extent) for over 20 years now. Example, electrical system in 2nd car I drove was stone dead and the ECU had apparently forgotten how to run properly (if it ever had completed it's learning cycle).

With the sophistication of the G6 ECU (most sophisticated GM makes), I think it is likely that the ECU requires an extensive learning cycle - and that it's programming is constantly tailored by how you drive. You may want to put a few hundred more miles of easy driving on it before passing final judgement on mileage.

The G6 I purchased performed marginally when I first drove it (7 miles on it). I refused to accept the car until I had driven it enough for the engine to start performing similar to the first one I drove (took about 15 miles). Since then it has performed better and better, the more it is driven. It now has 480 miles and is performing as I expect it to. 55mph mileage (level open road) on the DIC was recently 29.8mpg. Last tank's average (combo city/highway) was 18.9mpg by DIC. The DIC seems to be pretty accurate.

Enjoy your new car,

LM
 

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Discussion Starter #13
ive been getting about 17.5-19 mpg on a combine and if i really run easy at like 60 on the highway i do see 28mpg, but now at idle my engine runs rough almost feels similar to my 500hp v8 in my 85 grand prix
 
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