C7 AFM / Transmission issues.

Paulus

Regular user
Hi,
Has anyone with a C7, Z51 with A8 automatic transmission, come across shuddering problems
which seem on the US forums, to be attributed to the AFM operating between V8 and V4, modes, this
in turn causing possible damage to the torque converter and causing fluctuating rpm readings?
Cheers!
 

Stingray

CCCUK Member
My A8 is an early 2015 car so ticking towards it's fifth birthday already. I've recently had the recommended transmission fluid change. The old type of fluid can absorb water whereas the latest magic juice from Mobil 1 can't. The fluid change should prevent any torque converter problems.

I've also bought a "Range Technologies AFM Disabler". This plugs into the OBD port and puts the car permanently into V8 mode without any changes to the onboard programming. It makes for a nicer drive in situations where the engine would otherwise be shuffling between 4 and 8 cylinder operation. [edit: US market] A8 cars will otherwise use AFM in all driving modes and in all gears, unless shifted to Manual. [edit: It is said that Euro A8s behave the same as M7 cars, with AFM in Eco mode only. See later in this thread.]
 
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Paulus

Regular user
My A8 is an early 2015 car so ticking towards it's fifth birthday already. I've recently had the recommended transmission fluid change. The old type of fluid can absorb water whereas the latest magic juice from Mobil 1 can't. The fluid change should prevent any torque converter problems.

I've also bought a "Range Technologies AFM Disabler". This plugs into the OBD port and puts the car permanently into V8 mode without any changes to the onboard programming. It makes for a nicer drive in situations where the engine would otherwise be shuffling between 4 and 8 cylinder operation. An A8 will otherwise use AFM in all driving modes and in all gears (unless shifted to Manual).
My A8 is an early 2015 car so ticking towards it's fifth birthday already. I've recently had the recommended transmission fluid change. The old type of fluid can absorb water whereas the latest magic juice from Mobil 1 can't. The fluid change should prevent any torque converter problems.

I've also bought a "Range Technologies AFM Disabler". This plugs into the OBD port and puts the car permanently into V8 mode without any changes to the onboard programming. It makes for a nicer drive in situations where the engine would otherwise be shuffling between 4 and 8 cylinder operation. An A8 will otherwise use AFM in all driving modes and in all gears (unless shifted to Manual).
Hi.
Thanks for the info!
I assume you have'nt had any 'shuddering problems' with the A8? My enquiry is more prevention rather than cure.
My C7 is 2018 less than 2K miles.
I am aware of the range disabler which has had good reports, so I think I'll invest in one and as you say,
shuffling between the two modes can't be as good for the car and the drive, think it's GM's way of cutting fuel and emissions.
Also think I'll get a fluid change too to make sure the right 'juice' is in.
If there are problems, GM have reccomended a 'triple flush' apparently, on the transmission.
(Not sure whether they mean using flushing fluid, or three seperate fills with running time between flush??)

Again, many thanks for your response!
Cheers.
 

Stingray

CCCUK Member
A "triple flush" was used in early days and was then been found to be unnecessary. The transmission fluid has continued to be developed and the latest version only went on sale around March this year. It's supposed to be fancy stuff and to do the trick. (The triple flush was used because a proportion of old fluid can't be drained as it's sitting in the torque converter. If the car is driven between consecutive fluid changes it all gets stirred round and the old fluid is diluted a bit more with each change.)

My 2015 car is out of warranty and is a US import in any event - there were no Euro A8s - early Euro C7s were "manual only".

A preventive fluid change certainly can't do any harm.

If you have a 2018 then my understanding is there's no recall to change the fluid but it will be done under warranty if you encounter problems. When they do the change under warranty they just change the fluid, not the filter/screen.
 

Paulus

Regular user
A "triple flush" was used in early days and was then been found to be unnecessary. The transmission fluid has continued to be developed and the latest version only went on sale around March this year. It's supposed to be fancy stuff and to do the trick. (The triple flush was used because a proportion of old fluid can't be drained as it's sitting in the torque converter. If the car is driven between consecutive fluid changes it all gets stirred round and the old fluid is diluted a bit more with each change.)

My 2015 car is out of warranty and is a US import in any event - there were no Euro A8s - early Euro C7s were "manual only".

A preventive fluid change certainly can't do any harm.

If you have a 2018 then my understanding is there's no recall to change the fluid but it will be done under warranty if you encounter problems. When they do the change under warranty they just change the fluid, not the filter/screen.
I understand now the 'triple flush' that makes sense now thanks.
My car has a warranty with the dealer I purchased it from for 12mths, but not one with GM,
I will get it done as a precaution myself this being my choice, as you say, there are no recalls
to change it. At least I'll know whats in it and I'll get the filter and screen done too.

Many thanks again!
 

Chevrolet

CCCUK Member
Paulus, Before buying the AFM Range Disabler (for your US spec car?):

How long have you had the car/ Have you actually noticed the car go into V4 in a driving mode other than Eco? You have a 2018 car, I have a UK spec 2017 auto. I think that GM may have changed things (2017?) since the earlier cars, and they do not go into V4 in driving modes other than Eco which, as you know, is the default mode when you start the car. Look in your handbook. In mine on page 197, there is a chart that says AFM is "Normal" in all driving modes except Eco. I take that to mean "running in V8/all of the time" in all driving modes except Eco? I found a US Forum discussion which seemed to confirm that. One of the club members with a 2018 UK spec car, says that is how it is with his. Only had mine a few weeks and cant say I have noticed it going into V4.

On that Range Technologies website, one of the FAQs is about whether installing the AFM Disabler will affect the operation of the C7 exhaust. In their explanation, they include the chart I have in my handbook. So if the above is true, no reason for buying one, as long as you shift out of Eco when you start up?
 
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UKBeancounter

Committee Member
My 2017 starts up in "Tour" rather than "ECO". AFM cuts in across all drive modes, including "Track". Any time the engine is not under load it will cut down to 4 Cylinders. One of the dash displays shows this (I think its the display with the average fuel consumption). The drop down to 4 Cyl is un-noticeable, but the swap back to 8 is usually accompanied by a momentary "pinking" sensation/noise - remember those days on your 2-stroke LC350 (perhaps not !).
 

Stingray

CCCUK Member
Range AFM Disabler doesn't affect exhaust sound.

C7 has two completely separate sets of exhaust flaps, one set operated by the car itself when it switches between 4 and 8 cylinder operation and the other set operated by the driver to change the exhaust sound. In permanent V8 mode the first set of flaps will always be in V8 position. The driver can still set the sound with the other set according to taste....
 

Stingray

CCCUK Member
UKbeancounter - your car sounds to be operating exactly the same way as mine, which is a 2015 import.

Is your 2017 Euro or US import?
 

Chevrolet

CCCUK Member
Just found this quote on the Cadillacforums.com from 2 months ago. So looks like we are all right. The "export" C7s are set up differently to US spec cars:

"The export C7 generation Corvette disables AFM (active fuel management) for automatic equipped Corvettes unless driver mode is set to Economy but the U.S. version leaves AFM on in all modes including sport and track modes. ALL manual transmission Corvettes turn off active fuel management EXCEPT when set to Eco mode. As you would expect, running an 8 cylinder engine on only 4 cylinders results in a considerable increase in NVH and since they don't have a torque converter to abuse and use to soak up this added vibration with the M7 transmission, the designers couldn't use it as aggressively with manual transmission versions. AFM is extremely active on base, Z51, and GS level Corvettes but with the Z06, AFM it is only rarely active because the decreased compression ratio of the supercharged engine combined with the added drag of the downforce adding aero pieces and wider tires greatly limits where AFM can function. Basically steady cruising speed between 50-70 MPH and briefly during reduced throttle while slowing down from a higher speed are the only times AFM is engaged with a Z06. If you order the ZR1 variant, you get the engine version without AFM but the Europeans can't order this variant because this version of the LT series V8 engine uses a larger displacement supercharger which sticks up too high to meet EU pedestrian safety standards.

Hopefully the GM engineer who developed AFM bought stock in the company which sells the Range device so at least there is some logical reason for the existence of this automotive perversion."
 

UKBeancounter

Committee Member
UKbeancounter - your car sounds to be operating exactly the same way as mine, which is a 2015 import.

Is your 2017 Euro or US import?
US import as well.
Chevrolet - that explains a lot if the Euro versions are different.
On a run I have achieved 30 US mpg in Tour mode (can’t bring myself to use ECO on a V8) which is pretty incredible for a 6,2 Ltr engine. I personally don’t mind the V4 when cruising. It would be nice if it was switched off in Sport and Track however.
 

Bob Chevy

Regular user
I agree with the above, on my 2019 auto euro spec Grand Sport V4 mode only cuts in during eco settings on all other settings the V8 display is permanent I tried coasting with no throttle downhill and it stayed in V8.
The handbook is a little confusing, I almost ordered a range technologies after having the shudder problem on my previous Gen6 Camaro after 3000 miles that was sorted with the triple flush under warranty.
C5 YNK (Mick) who has a 2018 C7 auto has also confirmed with me V4 mode only works in eco mode on our euro spec cars.
 

Paulus

Regular user
Hi Chevrolet,
Mine is the US version 2018, so AFM is in all modes except manual, where it stays in V8 all the time.
I would be nice as beancounter said, if it stayed in V8 (specially in track and sport!). You can monitor
it shuffling about on the display and it does it very agressively (probably anything over 30 and you're
down to 4 cylinders). The US fourms I've been looking at say that you can end up with anything
from balancing/vibration issues to excessve cam wear and anything inbetween??! Probably a bit
excessive but who knows! In my case it may be better to invest in the range gadget?

Thanks guys!!
 

Stingray

CCCUK Member
It's all very curious. The online owner manuals for C7 Stingray in both US and Europe all say the same thing about AFM,

Europe

2015 - “With a manual gearbox, the system is only active in EcoMode.” Note: There was no auto A8 option available in Europe for 2015.

2016 - “With a manual transmission, the system is only active in Eco mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco mode.”

2017 - “With a manual transmission, the system is only active in Eco mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco mode.”

2017 Grand Sport – “With a manual transmission, the system is only active in Eco mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco mode”

2018 - “With a manual gearbox, the system is only active in Eco Mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco Mode.”

USA

2015 – “With a manual transmission, the system is only active in Eco mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco mode.”

2018 – “With a manual transmission, the system is only active in Eco Mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco Mode.”

2018 Grand Sport – “With a manual transmission, the system is only active in Eco Mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco Mode.”

2018 Z06 – “With a manual transmission, the system is only active in Eco Mode. With an automatic transmission, the system is available in all modes, but is more aggressive in Eco Mode.
 
N

Norm

Guest
With US model '16 Z06 A8, eliminated the Alternate Fuel Management 4 cylinder mode real quick, when I first heard that fart pipe sound in V4, that was it, never again.
To me now, I have the perfect sound combination, nice purr, no drone, and when I give it a little gas, screams like the devil.

To accomplish that, 3 things had to be done.
1. Disabled the AFM with a Range Disabler (about $200)
2. Pulled the fuse for the NPP exhaust (keeps butterflies in rear exhaust open)
3. Installed an X-Pipe that has no secondary cats (which are not monitored)(cost $420, 3 years ago)

Works perfect, sounds great.
 

Stingray

CCCUK Member
Update: Range AFM disabler works very well, getting rid of the very slight hesitation when you hit the throttle in V4 mode and the engine changes to V8. $189 well spent in USA.
I now have AFM disabler installed in the centre console via an OBD2 extension lead with on/off switch.
(Note. So far as I'm aware the disabler should not be switched on/off while the engine is running.)

Norm, out of interest which fuse did you pull for the exhaust? I know it's not identical but is the effect materially different from selecting "track" on the menu?
 
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Norm

Guest
In my engine compartment fuse box, for my NPP valves (2016) to stay open, I pulled fuse 42 (EXH VLV 2).
I never keep it in track mode when normal street driving, I used track for the track only, which I don't go anymore. I keep it T (touring) only, doesn't hunker down the suspension and makes for easier steering (if you have the selective mag ride option).

By pulling the fuse, the open exhaust flaps stay open constantly, regardless of what drive mode you're in.

Have fun with it, I sure do mine.
 
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Paulus

Regular user
Tried to purchase Range AFM from ebay off ivasoare6 two weeks ago. Never received it and no reply
from emails sent.... beware!!
Will have to go to the states for one unless anyone knows a supplier in the UK??
 
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Stingray

CCCUK Member
Norm - Thanks for the fuse location/number. As regards switching the exhaust I didn't mean the mode selector knob on the centre console which changes a number of other parameters at the same time. I meant the engine sound menu in the centre screen which changes the exhaust sound separately from anything else. I've heard it said that even in Loud mode the valves close some of the time, but have no evidence to back that up.

Paulus - It's my understanding that Keith Beschi at Eurovettes would be able to supply.
 
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