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Discussion Starter · #1 ·
I was speaking with a fellow Acadia owner in regards to our gas mileage and they said they heard there was a way for the dealer to do something to the car to make it get better gas mileage. I'm assuming they meant the trans flash as that in theory should improve some things, but is there something else anyone has heard about this? Kinda seems unbelievable if true...why wouldn't they just do it from the start. I'm skeptical and don't see this as being the direct reason for the reflash, or whatever it is. More possible that it is an indirect result of correcting something else.
 

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Seems extremely unlikely to me. In fact, I have no doubt that the reason we have the transmission issues we do, is that the transmission programming was over done in the quest for getting the last fraction of a mile per gallon out of the package. Its that same mileage issue that will make it tough for them to remedy the complaints. It would be no bid deal for them to program the transmission to shift in a more satisfying way (from the prospective of making power) but that would cost fuel mileage that they are already committed to with their EPA certification. They are going to have to work very hard to improve the flash programming and not LOSE miles per gallon IMHO.
 

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I think in real world driving fuel economy my not suffer or could improve with the reflash. With the original programming it was done for EPA certification and advertising, but with real drivers driving under real conditions this is not practical. I think drivers get frustrated with the lack of response and floor the accelerator to get the desired power they need, but with the reflash hopefully the trans will drop down into the proper gear without having to floor it and give the acceleration needed. It will never be or feel like a hot rod, but it should be better than it is.
 

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My highway MPG has actually gone up since the flash. I was at 24.4 yesterday. Thats about one mpg better than before. +or- .
 

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I've had the flash done and don't notice much difference in the way the vehicle shifts, however, I think my MPG might be improving. I haven't been through an entire tank yet, but just from the miles I've got on the trip already and how much gas I've used, it appears that my MPG has improved. Once I finish this tank, I'll post the results. :)
 

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Discussion Starter · #6 ·
Thanks all. I originally posted this before much of the hoopla from the other Trans Flash post had occurred. I too have had my trans flashed and my initial tank of gas took me up to 19mpg, whereas I used to get 13-14. I just filled up again recently it was back to the 14mpg from half tank. I'll keep monitoring mine and post results if they improve. I'm following a few of the other trans flash threads and it seems alot of people are seeing improved gas mileage as well.
 

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We had been getting pretty much the same MPG with latest reflash in 60F+ temps. What we really have noticed is the new responsiveness at any speed. Press down on the pedal a little bit and takes off in town. Doing 55mph on interstate, put peddle to the medal, it takes off right away with a little more umpf too. Shifting is really smooth whether on inclines with the 6 cogs too. This latest reflash was intended to reduce response time, hesitations, lags, and to smooth the 6 cogs out. The GMC Tech that did our reflash knew what he was doing and we now have the perfect set-up! We love everything about our SLE Acadia!! Our car must have been built on a T,W, or Th and will only take it in for any work at dealer on those days too. Hwy: 23-24 mpg average. Wife in town - 18/19 with temps 60F+ w tire pressure 40 lbs[cold]. My wife has a lead foot and corners on 2 wheels. I am more conservative but am not a granny by all means! Our engine and trans are rock solid with high performance satisfaction.
 

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teetertotter said:
We had been getting pretty much the same MPG with latest reflash in 60F+ temps. What we really have noticed is the new responsiveness at any speed. Press down on the pedal a little bit and takes off in town. Doing 55mph on interstate, put peddle to the medal, it takes off right away with a little more umpf too. Shifting is really smooth whether on inclines with the 6 cogs too. This latest reflash was intended to reduce response time, hesitations, lags, and to smooth the 6 cogs out. The GMC Tech that did our reflash knew what he was doing and we now have the perfect set-up! We love everything about our SLE Acadia!! Our car must have been built on a T,W, or Th and will only take it in for any work at dealer on those days too. Hwy: 23-24 mpg average. Wife in town - 18/19 with temps 60F+ w tire pressure 40 lbs[cold]. My wife has a lead foot and corners on 2 wheels. I am more conservative but am not a granny by all means! Our engine and trans are rock solid with high performance satisfaction.
I wish I was that satisfied with my SLE since the trans flash. :-\ That flash was the worst thing I could have done to my Acadia. I *knew* I shouldn't have brought it in for it. I had reservations about it. But I did it anyway. So I have no one to blame but myself. *shrugs* My mpg has suffered dramatically... Initially it seemed it might have improved, but that wasn't the case at all. I went from 24+ mpg Hwy to barely 19mpg Hwy. I don't notice much difference in the way the trans shifts, but again, I didn't really have a problem with it previously. And, now I get to "live with" my entire vehicle vibrating at 45mph. :eek:hno:
 

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I would doubt the transmission reflash by itself could have such a dramatic drop in mpg. It is more likely another problem or something else has changed- like winter blend gasoline, different usage (more city/less highway), etc. I track my mileage with every tank and haven't really seen a significant change in mpg when comparing similar trips before and after the flash.
 

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My milage down somewhat since the flash, shifts ok, but makes sense it would go down since it is not so much in a hurry to get into 6th gear. :confused:
 

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Does anyone know if this tranny "flash" applies to the 2008 models? I am getting 18 mpg (highway)in my 2 week old Acadia and I was expecting it to be closer to 20.
 

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rdgagnon said:
Does anyone know if this tranny "flash" applies to the 2008 models? I am getting 18 mpg (highway)in my 2 week old Acadia and I was expecting it to be closer to 20.
Some of the 2008s have the updated software right off of the line, however, the ones that were built prior to the update being available need to have the flash done to get the latest update. If I remember correctly, the cutoff date was sometime in mid or early September. I could be wrong though and I'm sure someone else will correct me appropriately on the date. Otherwise, i think a search of the forums will probably reveal the answer.
 

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My '08 was built in August. The dealer did the flash in November. Just checked my mileage this evening -- DIC indicated 18.5, manual calculations came to 18.9. This was all city driving. Granted, OKC is not bumper to bumper with stoplights every 2 blocks, but I feel that this is good MPG considering the power and size of this vehicle. The few roadtrips its been on have averaged about 23 MPG. Everything considered, I'm pretty satisfied.
 

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Had reflash done two weeks ago. I like the new feel of shift points, but MPG went frm 18 to 16mpg driving same route, according to DIC. It is very interesting the difference in MPG across the board among Acadia owners.
 

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I think it is much more likely that the winter gasoline blend is what is causing the drop. We have the same 10% ethanol blend here year round, so that is not a factor for me. I make the same trip (the interstate part is the same, slightly different destinations) several times each year. Here are the numbers (calculated manually)...

Before flash...
01-Apr 22.0
12-Apr 22.9
17-Aug 21.4
Weighted average = 21.83

After Flash...
05-Nov 22.7
30-Nov 21.2
Weighted average = 21.91

Factoring in different air conditioning loads, slight differences in gas pump shutoffs, slightly different destinations- I would say that the flash by itself definitely does not cause a significant drop in mpg. There has to be another factor. My running average has actually increased from just under 18 mpg overall to just over 18 overall (almost 12,000 miles) but I think that is most likely from cooler temps (lower AC load).
 

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Wow! If your averages are right, I wonder what is causing my drop. I averaged 18.6 in Aug., Sept, and Oct. in Houston. Since the flash my November average (going the exact same route) is down to 16.4. I still fill up at the local Kroger and have changed nothing. My tire psi is down 1 unit, but I try to keep it at 25.

If this isn't the reflash, any suggestions?
 

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mckcab said:
Wow! If your averages are right, I wonder what is causing my drop. I averaged 18.6 in Aug., Sept, and Oct. in Houston. Since the flash my November average (going the exact same route) is down to 16.4. I still fill up at the local Kroger and have changed nothing. My tire psi is down 1 unit, but I try to keep it at 25.

If this isn't the reflash, any suggestions?
Is it a typo that you keep your pressure at 25? Mine is at 35 per the spec.
 

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OOPS. I meant 35!!
 

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mckcab said:
If this isn't the reflash, any suggestions?
A few guesses, they may not apply at all but...

1. Colder weather, remote starting and longer idle times.
2. Though you do the same trip, there is more traffic- people out x-mas shopping, more sitting in traffic.
3. Lower tire pressures- especially in the morning due to lower temps.
4. Kroger gas comes from the cheapest source- so even though you buy at the same place, it may not come from the same supplier each time.

My mpg numbers above are correct. I keep a spreadsheet and update with each fill up. This is an almost all highway trip from Baytown to Lake Charles. There is no elevation change to speak of, so the transmission pretty much just goes into 6th gear and stays there for two hours each way. It would make sense that the programming would have very little effect on a trip like this (or any other true "highway" trip).
 
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