GMC Acadia Forum banner
1 - 20 of 49 Posts

·
Registered
Joined
·
683 Posts
Discussion Starter · #1 ·
Vehicle: 2007 Acadia SLE AWD, no tow package, no DIC. Current mileage is approx 13,500.

Background Maintanence: Has had both Tranny Flashes completed over 6 months ago

Description of condition: Shifts are very noticeable(feel and hear) and tend to come on very quickly. The transmission must still be trying to get the best mileage out of it as it works to get to 6th gear as quickly as possible. Result is very fast 1-2/2-3 shifts and continues until it gets to 6th gear. Notice a shift occurs in mid turn with normal throttle use causing an awkward nosedive, herky/jerky for lack of a better term. But please don't confuse this statement as hesitation, its just that the timing of the shift happens at a very unopportunistic time(mid turn). As I continue to accelerate the RPMs barely get past 2800 RPM before the next gear change. In fact the 2-3 shift happens literally less than 2 seconds after the 1-2 shift and the RPM level never even changes. When I finally reach a cruising speed of 45-50mph, 6th gear kicks in and the RPMs drop all the way down to 1200. When the RPMs drop this low, the engine noise is dramatically deeper and trucklike. Depressing the throttle allows the RPMs to raise and the noise goes away until I let off the gas to cruise again.

My gas mileage is poor at best, averaging only 12-14mpg since new. I drive mostly city and my commute is only 7 miles of stop and go conditions at an average speed of approx 45mph. Aside from me (175lbs) and a small lightweight stroller, I'm not lugging around anything heavy to put additional load on the vehicle. I am a bit more aggressive with the throttle and will typically drive 5-10 mph over the posted speed limit, however I tried to consciously do all the right things to monitor my speed, be more conservative with my acceleration, lift off the brake sooner to coast to a stop, etc...for an entire tank of gas and it didn't change my mileage. I've come to just accept that this is all she's got.

I have tried to manually shift the transmission, and/or just leave it in 5th gear the entire time. What I found is that my gas mileage does not seem to change at all, but the low RPM problem goes away at the 45-50mph cruising speed. RPMs stayed up around 1600 instead. However the RPMs do drop off to 1200 and result in the trucklike engine sound now at speeds of 35-40mph.

I also seem to feel that the transmission tends to sound like it is flaring just before a shift to a higher gear. It is like the RPMs shoot up quickly to change the gear and then drop off once the new gear is in place. Maybe I am becoming too sensitive to the transmission now, but it just doesn't seem right.

Does anything in what I have wrote above sound normal, or are there suggestions/fixes for what I described? Thinking about getting the transmission fluid changed for the flare up issues, but I wouldn't expect that to fix the shifting issues/low RPM/poor mileage.
 

·
Registered
Joined
·
956 Posts
I had my trans re flashed with the May re flash and it helped, but is no way near perfect. If you remember that this engine works best above 1800 rpm and keep it in that range you will be much happier. In town I select L3 or L4 depending on the speed, and on the freeway L5 or L6 depending headwinds, hills and traffic conditions. This seems to work well.
 

·
Registered
Joined
·
683 Posts
Discussion Starter · #3 ·
How is your mileage when you are using L3/L4 in town?

Were you/do you experience any of the other symptoms I described...the 1200 RPM range and the truck like sound? Or anything else?
 

·
Premium Member
Joined
·
14,870 Posts
Not that this will help; but I have had all trans flashes done and I am getting about 15 mpg around town, but that's what I expect. No noticeable sounds that I can think of
 

·
Registered
Joined
·
683 Posts
Discussion Starter · #5 ·
I drove into work this morning using the manual gear selector and limiting it to 4th gear. All the shift points seemed a bit smoother and there was no deep truck engine sounds. I was cruising at 45mph and the RPMs stayed at roughly 2000. Can't imagine this helping my MPG any, but I will say passing was much easier and smoother when running at the higher RPM. It just picked up nicely and moved. Whereas in the past when I was down at 1200 RPM in 6th gear, the RPMs had to shoot way up to get the car going.

I also recieved a personal message from a fellow forum member regarding the speeds at which the May 8th calibration were to set the tranny at. I have paperwork proving the dealership performed the flash, but my speeds seem to match up more closely to the pre-May 8th flash numbers. Anyone either notice if the tranny has reverted back to it old state or know if that is possible? Guess the only way to fix this would be to get the car into the dealership and have them take a look. I'm really concerned however that my MPGs are down to 12-14 now and the May 8th flash warns that the MPG will suffer worse afterwards... :eek:
 

·
Premium Member
Joined
·
14,870 Posts
imgntht said:
I drove into work this morning using the manual gear selector and limiting it to 4th gear. All the shift points seemed a bit smoother and there was no deep truck engine sounds. I was cruising at 45mph and the RPMs stayed at roughly 2000. Can't imagine this helping my MPG any, but I will say passing was much easier and smoother when running at the higher RPM. It just picked up nicely and moved. Whereas in the past when I was down at 1200 RPM in 6th gear, the RPMs had to shoot way up to get the car going.

I also recieved a personal message from a fellow forum member regarding the speeds at which the May 8th calibration were to set the tranny at. I have paperwork proving the dealership performed the flash, but my speeds seem to match up more closely to the pre-May 8th flash numbers. Anyone either notice if the tranny has reverted back to it old state or know if that is possible? Guess the only way to fix this would be to get the car into the dealership and have them take a look. I'm really concerned however that my MPGs are down to 12-14 now and the May 8th flash warns that the MPG will suffer worse afterwards... :eek:
It seems to vary between vehicles; but I haven't noticed a drop in MPG with all trans flashes done
 

·
Registered
Joined
·
1,164 Posts
imgntht said:
I drove into work this morning using the manual gear selector and limiting it to 4th gear. All the shift points seemed a bit smoother and there was no deep truck engine sounds. I was cruising at 45mph and the RPMs stayed at roughly 2000. Can't imagine this helping my MPG any, but I will say passing was much easier and smoother when running at the higher RPM. It just picked up nicely and moved. Whereas in the past when I was down at 1200 RPM in 6th gear, the RPMs had to shoot way up to get the car going.

I also recieved a personal message from a fellow forum member regarding the speeds at which the May 8th calibration were to set the tranny at. I have paperwork proving the dealership performed the flash, but my speeds seem to match up more closely to the pre-May 8th flash numbers. Anyone either notice if the tranny has reverted back to it old state or know if that is possible? Guess the only way to fix this would be to get the car into the dealership and have them take a look. I'm really concerned however that my MPGs are down to 12-14 now and the May 8th flash warns that the MPG will suffer worse afterwards... :eek:
If it's not shifting at the speeds indicated by the May 8 service bulletin, it sounds to me like they did not complete the May 8th flash correctly. I would print out the bulletin and go for a test drive with the service dept. to prove to them it isn't shifting at the proper points. Then insist they reinstall the May 8 flash.
 

·
Premium Member
Joined
·
3,212 Posts
I agree with loach here. It sounds like the May 08 update wasn't performed correctly.

The mpg numbers don't surprise me as you state it's 7 miles of stop and go driving. A commute of that short a distance is going to be spent getting the engine up to operating temperature so there is very little driving where the engine is running at peak efficiency, and stop and go driving is not this vehicle's strong point either as these things are so heavy.
 

·
Registered
Joined
·
6 Posts
Test driving an '09 tonight... What should I be looking for if anything with regards to this newest model?
Or are the '09s happy campers?
 

·
Registered
Joined
·
14 Posts
crossover4us said:
Test driving an '09 tonight... What should I be looking for if anything with regards to this newest model?
Or are the '09s happy campers?
Had our 09 for a couple of weeks... haven't been paying super close attention to the trans... but my casual observations is it performs well... upshifts are are quick and firm... downshift are also quick with no annoying delay... next time I take it out by myself, i'll take it for a more spirited drive than i might if I had the Mrs. with me... LOL! So yes, I am a Happy Camper...
 

·
Registered
Joined
·
683 Posts
Discussion Starter · #12 ·
Been spending the last few days just setting it in L4 and driving as normal. This thing really feels good in this mode around town and occassionally shifted into 5th gear on a short stretch of road where I can get up to 60. I'm going to keep this up and see how my mileage is. Judging by my previous experience leaving it in 5th gear all the time, and what GeoHawk noted above, I don't expect there to be much difference. So the only problem I see with this currently is that I tend to forget I am in the manual gears and when attempting to reverse I have frequently dropped it into Neutral instead ::) Doh! Just have to get used to move the shifter one space further forward. On my next scheduled oil change with the dealer, I will bring up the trans thing again and have the shift point speeds handy to reference.
 

·
Registered
Joined
·
1,048 Posts
I loved my update, but lately I have noticed a lag. Is it possible that whatever is cleaning out my door programs could also be resetting everything back to factory specs? The car was recallibrated for gas intake and it is chugging again and it has a big hesitation when trying to enter a freeway. It sounds logical, but is it possible?
 

·
Registered
Joined
·
3 Posts
Maybe this has been discussed elsewhere but we just got an 09 and I feel like it is too quick to shift down from 6th to 5th at highway speeds. Seems like any kind of head wind or mild hill will cause it to jump down. Putting it into manual selection and running in 6th seems to help but I'd rather it just hold 6th longer. Can a dealer adjust just the logic that causes it to downshift from 6th?
 

·
Registered
Joined
·
6,233 Posts
I wonder if using "L" puts any unnecessary strain on the tranny? Or is it actually less wear since presumably there are fewer shifts.
 

·
Registered
Joined
·
428 Posts
It actually should be less wear since the transmission is shifting less it is definanatly less wear on the clutch bands in the transmission.
 

·
Premium Member
Joined
·
3,212 Posts
benalbright said:
Maybe this has been discussed elsewhere but we just got an 09 and I feel like it is too quick to shift down from 6th to 5th at highway speeds. Seems like any kind of head wind or mild hill will cause it to jump down. Putting it into manual selection and running in 6th seems to help but I'd rather it just hold 6th longer. Can a dealer adjust just the logic that causes it to downshift from 6th?
There's no programming updates for the 09s. The problem lies with a relatively low torque engine running at such low rpms in 6th gear. Supposedly the 09s downshift even less than the 07s and 08s. There's no real good way to get around it. Welcome to the forum Ben. :)
 

·
Super Moderator
Joined
·
22,405 Posts
there is a bit of a way around it Hawk - start out a bit smarter (faster), don't be the last one leaving the stoplight when you're the first in line!!

:sleepy:
 

·
Registered
Joined
·
179 Posts
benalbright said:
I feel like it is too quick to shift down from 6th to 5th at highway speeds. Seems like any kind of head wind or mild hill will cause it to jump down. Putting it into manual selection and running in 6th seems to help but I'd rather it just hold 6th longer.
It's not actually downshifting most likely. What you are noticing is the torque converter releasing and applying. It's still in 6th gear when you see the rpms go from 2000 to around 3000. Driving in L6 is no different than D either. It's the same thing. You might like it to hold 6th longer, but there just isn't enough torque there. You wouldn't like it if it did anyway. Just ask anyone with a 2007 or 2008. It held 6th a bit longer, but then you had to press the pedal too far to get any kind of response out of the vehicle and then once you did, it was usually more than you wanted because you got a downshift into 5th and the torque converter release.
 

·
Premium Member
Joined
·
14,870 Posts
The gearing on 6th gear is such that almost any load on it will cause it to downshift:

Transmission& Power Take Off Unit (PTU)

Gear Ratio :)1)




First: 4.48


Second: 2.87


Third: 1.80


Fourth:1.47


Fifth: 1.00


Sixth: 0.74[/color]


Reverse: 2.88
 
1 - 20 of 49 Posts
Top