Subaru Ascent Forum banner

21 - 40 of 68 Posts

·
Registered
Joined
·
206 Posts
Discussion Starter #21
One of my gripes is more CVT related and how the ECU/TCU work in conjunction. In every other (auto transmission) car I've owned, when you go up an incline, the transmission stays in OD gear for as long as possible and then only downshifts when necessary. In the Ascent, if you fart out the window while cruising at speed, it automatically increases RPM (whether its the torque converter "unlocking" or the CVT changing ratios) which put more strain on the transmission. Rule of thumb always has been that you don't want the transmission "hunting" between gears because it accelerates wear, but that seems to be the way this CVT works. I'd much rather have the CVT remain in its "OD gear" and let the engine do the work. I can be cruising on the highway, CC on at 70 MPH and the RPM will jump to 2500 just because I'm going past an interchange with MINOR elevation change. By contrast my EcoBoost F-150 in this same situation would remain in 6th gear and the ECU would add boost (torque) to pull itself up the incline.
If it "is what is is" then so be it...but if there is any way for SOA to fix this or if the COBB tuning fixes this...then sign me up...drives me nuts!
This is exactly what the recall fixed for me.

I called my dealer who said the recall was issued in August 2019 and only applies to 2019 models. I have a 2020 built in Dec 2019. The dealer said it should have been taken care of at the factory and they would not do the recall. My CVT seems jumpy at times with sudden downshifts, or getting bogged down with upshifts when accelerating from a stop. The dealer would most likely say it's normal operation?
They might have looked up the wrong one. Here is the recall, issued Nov 2019

3571


3572
 

·
Super Moderator
Joined
·
6,510 Posts
I called my dealer who said the recall was issued in August 2019 and only applies to 2019 models. I have a 2020 built in Dec 2019. The dealer said it should have been taken care of at the factory and they would not do the recall. My CVT seems jumpy at times with sudden downshifts, or getting bogged down with upshifts when accelerating from a stop. The dealer would most likely say it's normal operation?
Your dealer is a little confused. The recall (Service Campaign) for the most recent ECU reprogramming is from November 22, 2019.

Here's all the details for the ECU Service Campaign:

Here's all the details for the CVT Recall:

Here's all the details for the PCV Recall:

You can check YOUR car here:
 

·
Registered
2020 CWP Touring
Joined
·
47 Posts
One of my gripes is more CVT related and how the ECU/TCU work in conjunction. In every other (auto transmission) car I've owned, when you go up an incline, the transmission stays in OD gear for as long as possible and then only downshifts when necessary. In the Ascent, if you fart out the window while cruising at speed, it automatically increases RPM (whether its the torque converter "unlocking" or the CVT changing ratios) which put more strain on the transmission. Rule of thumb always has been that you don't want the transmission "hunting" between gears because it accelerates wear, but that seems to be the way this CVT works.
I'll be the first to say that I'm not an expert on CVTs, I've owned a Subaru with a CVT for a total of 500 miles, and I'm still learning the Ascent. However, I'm a petrol-head at heart and have a pretty keen awareness of what's going on under my feet. And I've learned a lot about these things over the past few months as I've read up on them thoroughly prior to, and after, our purchase a few weeks ago.

I understand Subaru's CVTs use a slightly unconventional torque converter, one that is designed to remain engaged nearly all the time. It's not engaged at stop (obviously), and I'm fairly certain that the big "bog" felt while gently accelerating just after you get moving is the torque converter engaging. The initial "flash" up to about 2,000 RPM is when the torque converter is unlocked, then it locks and the engine speed falls to around 1,400 RPM or so. After this, I'm fairly certain that the torque converter stays engaged, pretty much until you stop again, and all engine speed changes independent from vehicle speed changes are due entirely to intentional pulley ratio changes.

You can verify this yourself by slipping the transmission into manual mode and using the paddle shifters. In this mode, and assuming you're driving at a speed appropriate for each gear, the CVT is "locked on" whatever pulley ratio is programmed for that "speed number". You can absolutely climb a hill in "7th gear", with the engine turning only 1,400 RPM. At interstate speed, put it in "8th gear" and it'll tool all day well below 2,000 RPM (depending on road speed), and that RPM won't change one bit. I don't think this is the best way to drive, however (despite it feeling more conventional).

Engine load goes way up, turbo boost goes way up, and you're actually putting a lot of strain on the CVT as well. I understand the higher pulley ratios in these CVTs are VERY overdriven -- meaning the output shaft may be turning twice or more for every one rotation of the input shaft. This is not common in conventional automatics (where the top gear is generally in the 0.70:1 range, or somewhere in there). Holding the CVT to a 0.50:1 ratio (if that's what it really is) puts a lot of unnecessary strain on the unit. You're basically removing its mechanical advantage and forcing a higher input torque to get the same output torque. You described it as "letting the engine do the work", but you're really forcing the whole system into a higher work load by doing this.

I think this is why the CVT is relatively quick to "downshift" on even slight hills. It's not unlocking the torque converter or engaging or disengaging any clutches. It's simply adjusting the pulley ratios to both:
  1. Increase the mechanical advantage of the transmission, and
  2. Decrease the load on the engine.
By increasing mechanical advantage of the drivetrain, engine speed goes up and load goes down. That's the basics, really, of any drive system, whether it's a stepped or variable transmission in a road vehicle, or a chain-and-derailleur system on a bicycle, etc. Both 1 and 2 above are desirable for long-term durability and reliability. I'm totally with you on the human desire for the engine to not constantly be changing and...when it does...it makes us think it's slipping or not as efficient. But I'm fairly certain that the way they've designed it is the best balance of all factors considered.
 

·
Super Moderator
Joined
·
6,510 Posts
Both 1 and 2 above are desirable for long-term durability and reliability. I'm totally with you on the human desire for the engine to not constantly be changing and...when it does...it makes us think it's slipping or not as efficient. But I'm fairly certain that the way they've designed it is the best balance of all factors considered.
And, keep in mind that with our super wide and super flat torque band of 277 lb-ft of torque from 2,000 rpm to 4,800 rpm, it makes sense to put us nearer the rpm for max hp as well. Max HP is at 5,600 rpm.
 

·
Registered
Joined
·
18 Posts
I'll be the first to say that I'm not an expert on CVTs, I've owned a Subaru with a CVT for a total of 500 miles, and I'm still learning the Ascent. However, I'm a petrol-head at heart and have a pretty keen awareness of what's going on under my feet. And I've learned a lot about these things over the past few months as I've read up on them thoroughly prior to, and after, our purchase a few weeks ago.

I understand Subaru's CVTs use a slightly unconventional torque converter, one that is designed to remain engaged nearly all the time. It's not engaged at stop (obviously), and I'm fairly certain that the big "bog" felt while gently accelerating just after you get moving is the torque converter engaging. The initial "flash" up to about 2,000 RPM is when the torque converter is unlocked, then it locks and the engine speed falls to around 1,400 RPM or so. After this, I'm fairly certain that the torque converter stays engaged, pretty much until you stop again, and all engine speed changes independent from vehicle speed changes are due entirely to intentional pulley ratio changes.

You can verify this yourself by slipping the transmission into manual mode and using the paddle shifters. In this mode, and assuming you're driving at a speed appropriate for each gear, the CVT is "locked on" whatever pulley ratio is programmed for that "speed number". You can absolutely climb a hill in "7th gear", with the engine turning only 1,400 RPM. At interstate speed, put it in "8th gear" and it'll tool all day well below 2,000 RPM (depending on road speed), and that RPM won't change one bit. I don't think this is the best way to drive, however (despite it feeling more conventional).

Engine load goes way up, turbo boost goes way up, and you're actually putting a lot of strain on the CVT as well. I understand the higher pulley ratios in these CVTs are VERY overdriven -- meaning the output shaft may be turning twice or more for every one rotation of the input shaft. This is not common in conventional automatics (where the top gear is generally in the 0.70:1 range, or somewhere in there). Holding the CVT to a 0.50:1 ratio (if that's what it really is) puts a lot of unnecessary strain on the unit. You're basically removing its mechanical advantage and forcing a higher input torque to get the same output torque. You described it as "letting the engine do the work", but you're really forcing the whole system into a higher work load by doing this.

I think this is why the CVT is relatively quick to "downshift" on even slight hills. It's not unlocking the torque converter or engaging or disengaging any clutches. It's simply adjusting the pulley ratios to both:
  1. Increase the mechanical advantage of the transmission, and
  2. Decrease the load on the engine.
By increasing mechanical advantage of the drivetrain, engine speed goes up and load goes down. That's the basics, really, of any drive system, whether it's a stepped or variable transmission in a road vehicle, or a chain-and-derailleur system on a bicycle, etc. Both 1 and 2 above are desirable for long-term durability and reliability. I'm totally with you on the human desire for the engine to not constantly be changing and...when it does...it makes us think it's slipping or not as efficient. But I'm fairly certain that the way they've designed it is the best balance of all factors considered.
Thank you!!! You wrote and explained what I simply did not have the time (or brain power) at the moment to write. You are spot on with all of your explanations and details of the relationship between engine, transmission and how gear ratios affect load on the motor AND transmission. Perhaps the programming on the CVT is more geared (pun intended) to prevent chain slip (high load "OD gear" situation) versus wear of constantly going back and forth between "ratios".
In the example of my F-150 Ecoboost...it was modded...downpipes, exhaust, intake, intercooler, charge pipes and a 93 octane tune. 389whp and 543wtq. There was a particular highway interchange that I would take at 65MPH (1500RPM) and as it would climb, I'd watch boost climb up to about 18-19 psi and it never skipped a beat. No knock, no other ill effects.Similarly, in a turbo diesel F-250 I used to own, towing a racecar across the country I'd have the CC on, 70-75 MPH and going through the mountains you'd hear the turbo spool up, but no drop in gearing...hell, it only did that on the decent in order to engine brake. This is what I'm "accustomed to".
The same overpass where the F-150 stayed in gear, the Ascent revs up to 2500RPM to maintain speed...and this is Florida, so i'm not climbing mountains! I can understand the reasoning behind programming the CVT this way...it just seems like more wear and tear having the CVT vary ratios constantly even if the vehicle speed is being maintained constant. Hell, going into a 15 MPH headwind this weekend, the revs were about 200RPM higher than normal for that speed.
This is my first CVT vehicle and it has taken some getting used to. I enjoy the smoothness of no shifts...but need to have the radio up to drown out the monotonous hum of the motor until you reach speed. watching the tach dance around on the highway drives me bonkers though! I've checked and there are no recalls for my vehicle...so I should be up to date on software. I have about 1300 miles on the clock.
Thanks to everyone so far...these forums are great!
 

·
Registered
Joined
·
206 Posts
Discussion Starter #26
And, keep in mind that with our super wide and super flat torque band of 277 lb-ft of torque from 2,000 rpm to 4,800 rpm, it makes sense to put us nearer the rpm for max hp as well. Max HP is at 5,600 rpm.
This doesn't make sense to me in any shape or form. If I can make it up the hill at 1,800 rpms just fine, why in the world would I instead want it at 3,000rpms? I don't need the extra power, I'm getting up just fine.

Even more funny, is the ECU update further justifies this. Old way was high RPMs on a hill, new way is MUCH lower RPMs. Ascent makes it up just fine with far less gas.

And lets be clear, when I say "hill", I mean something that people in Colorado would call a speed bump.
 

·
Super Moderator
Joined
·
6,510 Posts
Perhaps the programming on the CVT is more geared (pun intended) to prevent chain slip (high load "OD gear" situation) versus wear of constantly going back and forth between "ratios".
Nope.

Clamping pressure is regulated to prevent chain slip. We'd never be able to tow 5,000 pounds if your theory was accurate.

Fact is, the TR690 design was intended to constantly vary the ratio, and adjusted based on perceived need. Fake shifting was added because reviewers complained about the rubber band effect of not having shifting.

I, for one, cannot wait for them to get rid of the faux shifting that hobbles our performance, the smoothness we could be experiencing, and the slight fuel economy boost we could get when faux shifting is finally removed so the TR690 CVT can once again work as designed.
 

·
Super Moderator
Joined
·
6,510 Posts
This doesn't make sense to me in any shape or form. If I can make it up the hill at 1,800 rpms just fine, why in the world would I instead want it at 3,000rpms? I don't need the extra power, I'm getting up just fine
More engine strain, less efficient, heavier load on the slower spinning engine, potential stall scenario, etc, etc.
 

·
Registered
Joined
·
7 Posts
I figured we had the "poor MPG" and "my MPG is great" threads, figured I'd start a bridge/fixed thread.

Here is the original issues at hand for my 2020 Limited, and I believe a lot of you
  1. Overly sensitive throttle, impossible to precisely vary RPMs below 2,400rpm
  2. RPMs too high when cruising in city or hwy, manual shifting would easily lower by 500rpms or more
  3. Poor gas mileage (12-14mpg) in the city, even when using cruise control
  4. Poor gas mileage on the hwy (19-21mpg MAX), even when using cruise control 99% of the time
  5. Erratic and increasing RPMs when going up a hill for no apparent reason, even when reducing throttle
Last week I had the ECU Reprogramming recall performed and immediately I knew we were getting better MPG. After a weeks worth of driving this is what has been corrected (praises respective to complaints):
  1. Very easy to control lower RPMS, engine no longer goes from tons of power at 2,500+rpms to bogging at 1,500rpms - the bogging issue has not occurred once when it used to happen multiple times per day
  2. RPMs when using cruise (or not) in city and hwy are MUCH lower and where they should be - I can cruise through the city around 35-40mpg and the engine will be at 1,200rpms
  3. Gas mileage in the city, using the same habbits and routes, is now 20mpg every day
  4. HWY MPG is not fully vetted, partly due to COVID-19 and limited travel, but I have seen an improvement - just no hard data
  5. RPMs no longer go crazy when going up a typical hill, they stay constant even when letting off the throttle
Now, I have a few myths to bust (yes, not scientific) which some members claimed are the reasons for poor MPG:
  • Ascent is still being warmed up a few minutes prior to leaving for work and prior to coming home.
  • Driving style was not a factor. We continue to drive the Ascent the same as we did before, using a lot of cruise control still in the city and on the hwy. I attribute this to the lower RPMs for acceleration and cruising speed.
  • Temperature is still roughly the same. No crazy delta in the temp, still continue to have a lot of sub-freezing temps.
All in all, my wife and I are VERY happy with the improved MPG. She no longer says "we sold the Yukon to get rid of the 12-14mpg city driving".
I've had the same issues. It's been reprogrammed, fixed it momentarily, but its back to doing the same. Has nothing to do with a "touchy" pedal. If anything, maybe someone assuming it's a human response either doesn't have the same issue I'm having or doesn't try to drive in 20 mph school zones often. I'm ready to trade mine in after several tries at the dealership to fix it. Funny thing is, I told them there was an issue months before the recall finally caught up. I know they're on the right track because it did "fix" the issues for a few weeks... but, I'm not willing to keep riding it out until they finally figure it out.

Never had these issues with Ford, which we stuck with for 20 years. Say what you will about Ford, but I wish I'd stayed. I thought I was upgrading with an amazing brand in Subaru.. now I'm going to be out the money we put into it and I have to search again for a new vehicle.
 

·
Super Moderator
Joined
·
6,510 Posts
Then why is the problem gone.....
There wasn't a problem, and the Ascent will adjust based on a number of factors, regardless of ECU update.

I posted a link with details about what the ECU update did above.
 

·
Registered
2020 CWP Touring
Joined
·
47 Posts
Then why is the problem gone.....
It's probably important to keep in mind that the ECU update is to fix a specific programming problem in the module associated with a particular DTC (C1424). AscentForums link. This accelerator pedal position data element issue could very possibly be linked to any number of symptoms, including lurchy throttle, inconsistent throttle, improper fuel metering, etc.

Our February 2020 build Ascent exhibits some of the symptoms you describe (engine revving more than we might be used to on the highway, etc.), but it almost certainly has the programming "fix" built into it already (this programming fix was validated during 2019, so it would certainly be included on new builds from there). Perhaps the vehicles suffering from this problem had much more severe symptoms than most owners observe. Apparently so, if you were getting poor fuel economy as you were. Our Ascent is far from broken in (only about 500 miles on it so far), but we're averaging over 20 MPG with it (20.8) with a mix of typical suburban and semi-rural driving. Though our car does rev higher on the road when under any type of load (head wind, incline, etc.), it seems to get good fuel economy while it's doing it.

The hard part about internet forums is we can't directly compare the behavior of two different vehicles. What might be unacceptable to one person may go unnoticed by another.
 

·
Registered
2020 CWP Touring
Joined
·
47 Posts
In the example of my F-150 Ecoboost...it was modded...downpipes, exhaust, intake, intercooler, charge pipes and a 93 octane tune. 389whp and 543wtq. There was a particular highway interchange that I would take at 65MPH (1500RPM) and as it would climb, I'd watch boost climb up to about 18-19 psi and it never skipped a beat. No knock, no other ill effects.Similarly, in a turbo diesel F-250 I used to own, towing a racecar across the country I'd have the CC on, 70-75 MPH and going through the mountains you'd hear the turbo spool up, but no drop in gearing...hell, it only did that on the decent in order to engine brake. This is what I'm "accustomed to".
Nice vehicles -- I'll bet they were fun. My folks used to tow a 35k# travel trailer, and started with an F-550 with the 7.3L PS, but that wasn't quite enough truck for the trailer, so they upgraded to an F-650 SuperCrewzer with the Cat 3026B engine. Super cool truck.

The thing with these trucks (even the EB F-150) over our Ascent is the amount of reserve power they have. Even in stock form, the EB F-150 is rated to pull twice its weight in trailer, right? Truck probably weighs 6k#, and it's rated to tow 12k# or something similar? There's a lot of reserve capacity there (in everything...engine, brakes, suspension, etc.) and that results in fairly low-effort driving in most normal conditions. Pulling an incline into a headwind with no trailer and no payload is pretty easy -- because it's designed to haul twice its weight.

Our Ascents don't enjoy as much reserve capacity. We're rated to tow about our weight in trailer (4,500# vehicle and as much or slightly more trailer). Everything is on a smaller scale. Vehicle is lighter, suspension is lighter, brakes are smaller, engine is smaller, etc. It's still plenty capable of doing that...but an unloaded F-150 is only 33% of its combined vehicle weight rating. An unloaded Ascent is about 50% of its combined vehicle weight rating. (Again, just using rough figures here.)
 

·
Super Moderator
Joined
·
6,510 Posts
How to find build date we bought ours 12/26/20
We had to wait 2 days
Driver's door B pillar, on the black build plate near the bottom of the pillar, top right corner will be month and year.
 

·
Registered
Joined
·
18 Posts
Nice vehicles -- I'll bet they were fun. My folks used to tow a 35k# travel trailer, and started with an F-550 with the 7.3L PS, but that wasn't quite enough truck for the trailer, so they upgraded to an F-650 SuperCrewzer with the Cat 3026B engine. Super cool truck.

The thing with these trucks (even the EB F-150) over our Ascent is the amount of reserve power they have. Even in stock form, the EB F-150 is rated to pull twice its weight in trailer, right? Truck probably weighs 6k#, and it's rated to tow 12k# or something similar? There's a lot of reserve capacity there (in everything...engine, brakes, suspension, etc.) and that results in fairly low-effort driving in most normal conditions. Pulling an incline into a headwind with no trailer and no payload is pretty easy -- because it's designed to haul twice its weight.

Our Ascents don't enjoy as much reserve capacity. We're rated to tow about our weight in trailer (4,500# vehicle and as much or slightly more trailer). Everything is on a smaller scale. Vehicle is lighter, suspension is lighter, brakes are smaller, engine is smaller, etc. It's still plenty capable of doing that...but an unloaded F-150 is only 33% of its combined vehicle weight rating. An unloaded Ascent is about 50% of its combined vehicle weight rating. (Again, just using rough figures here.)
Agreed. But this is the way that I look at it (wouldn't be the first time I'm wrong...lol). How much TQ is the FA24 producing to push the Ascent through the air at 70MPH? Let's pretend its 75ft-lbs. How much TQ is needed when you add a 5% incline overpass? 100ft-lbs? Crack the throttle open a bit, add a little boost pressure and you're done. It just seems to me like its additional wear on an automatic tranny to change ratios on every little hill you go over. This is why on a traditional auto you disengage OD to prevent "hunting" while towing or going over inclines. I guess having that programmed into my brain for almost 30 years of driving to keep tranny temps down just sends off an alert every time the CVT starts shifting ratios to maintain speed.
 

·
Registered
2020 CWP Touring
Joined
·
47 Posts
Like you, I'm "programmed" to expect a constant engine speed at a constant road speed. I have played a lot with manual mode in our Ascent, replicating that...if even for my own enjoyment or amusement. I'm learning, though, to appreciate the fact that the CVT is not burdened by a choice of only a relative few gear ratios, and it's free to traverse the entire range of available ratios to best manage the demand at that specific moment in time. I also have to tell myself, "the transmission is not slipping," and, "the torque converter isn't unlocking, wasting fuel."

I'm not a Subaru powertrain engineer, and I certainly couldn't say for sure what the compelling reason is for so quickly shortening the ratio for headwinds or inclines. Maybe it's fuel economy (maybe the engine is really more efficient at 2,200 RPM at a moderate load than it is at 1,800 RPM at a heavy load). Maybe it's engine durability (smaller 4-cylinder engine with a lot of cylinder pressure doesn't like high load/low RPM operation). Maybe it's transmission durability (operating at the lowest mechanical advantage all the time, like 8th speed, puts all internals under higher pressure). The only thing I'm really confident about is there must be at least one good reason for it. :)

I think it's a pretty novel design that I'm only now getting personally introduced to (and learning to like). I wish Subaru had been on my radar long before now!
 

·
Registered
Joined
·
534 Posts
CVTs have been around a long time. I first came across them in the early '60s on snowmobiles and ATVs. Those were rubber belt types, of course. These would change ratio based on the the action of fly-weights that would change the pulley flange spacing as a function of rpm. There are other types as well.

I think Nissan was the first major manufacturer to put a CVT in a main stream full size vehicle, the Murano, back in 2002. Of course the whole point of a CVT is that it can continuously vary it's ratio rather than be stuck in one or interrupt operation to make discrete jumps between fixed gear ratios. It really takes no effort for it to continuously change ratio to whatever is optimum for the situation as the situation changes. Again, that's really the whole point of it. If it's not doing that, you might as well have a regular geared transmission.

To propel a vehicle against fiction and aerodynamic drag, or up a hill, takes torque and rpm. The product of torque and rpm is power. A given situation will require a given power, and the that power can be acheived either at a lower rpm with higher torque, or a higher rpm with lower torque. Up to a point, the latter is often less stressful on a drivetrain.
 
21 - 40 of 68 Posts
Top