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[ANSWERED] Why can you not just disable the AFM?

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[ANSWERED] Why can you not just disable the AFM?

 
Old 06-12-2017, 03:47 PM
  #21  
NSC5
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I understand AFM for fuel economy but I (and probably most owners) if given a choice between keeping the torque converter locked during V4 mode and feeling additional engine vibration (like the M7 owners) or having to deal with multiple very invasive torque converter replacements the choice would be an easy one to make. Or if concerned about customer complaints GM could do like they did with the heated windshield washer fluid issue, disable the modulated lock-up clutch during V4 operation and give the customers a small check for losing the feature. I would be happy to lose the modulated torque converter during V4 mode with no compensation but for PR and legal reasons if GM would feel better about the same $100 check that we got for losing heated washer fluid I expect a huge number of owners would jump on that and it would save the company a lot of warranty costs in trying to overcome this shudder issue.

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Old 06-12-2017, 05:07 PM
  #22  
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Originally Posted by vettetwo View Post
GM has perfected start/stop extremely well. I have a 2017 Cadillac XT5 which starts within .3 seconds of lifting your foot from the brake and recharges the AGM battery when coasting (rather than costing) or braking to minimize power consumption of the alternator. My first exposure to start/stop was a 2015 Malibu rental while on vacation in California. I drove it for a couple of days before I noticed the autostop position on the tachometer. After seeing that, I watched each time I stopped and it was engaging nearly every time. The new 8-speed transmission was designed for start/stop to shift to neutral before the engine is stopped when the autostop engages. That minimizes the load on the engine bearings because the oil pump is driven by the engine. It takes too much power to drive electrically so the oil must be minimally semi-synthetic to maintain an oil film on the bearings for nearly instant load when restarting after autostop.

I think the biggest objection to autostop in the Corvette is the sound of the exhaust at idle and owners would object to a silent Corvette when stopped. That is why hybrid Corvettes will loose a lot of long time enthusiasts. Would you want a silent Corvette or silent Harley Davidson?
Thanks for the response. There were a couple of negative comments that complained and sited my post, perhaps without every trying a good start/stop, i.e. short battery and started life, it doesn't save much gas etc! Don't see them now, perhaps they deleted the comments!

Posted the pic below some time ago. It shows the internal combustion engine is very inefficient by it's nature. Granted it depends on the type of driving but that average data shows 17% of the energy is wasted idling! Also as significant, of the 13% of the energy in gasoline than gets to the rear wheels, about a 1/3 is ultimately wasted braking! Again the numbers are dependent on just how you drive but some of that wasted idling fuel can be saved with start/stop.

Re the battery/starter life. Yep need and AMG or better battery. That is what is in our BMW SUV. Starter motors can be made more rugged. In fact I have a small starter motor in my ProStreet Rod, it's gear driven. It spins that 8.2 Liter high compression engine with no trouble!

But more important than a "better starter motor," just like the Vettes very complex procedure for shutting the exhaust and intake valve separately when they switch to V4, to maintain cylinder pressure in the cylinders shut off, many companies shut off the engine for start/stop when there is pressure remaining in the combustion chamber! That pressure starts the engine with little help from the starter motor! Reminds me of starting WWII fighter airplanes with an artillery shell charge! (In fact, in my "man cave" I have one cylinder, a piston and master connecting rod from an 18 cylinder R2800 that was used in the Corsair! That ~2500 hp engine must have been fun to start!)

I'm not a tree huger. In fact the 8.2 Liter BB in my ProStreet Rod with 16.5 section width Mickey Thompsons gets about 10 mpg the way it's geared! However where technology can help improve efficiency, why not! As I mentioned in my first post on this thread, love to have 160 motor driven hp for ~6 seconds and that same motor charging the battery when I'm coasting or braking-like an F1 race car!

As I also said in that post, for the sound issue- provide selectable options when stopped, of having the sound system play a: 12 cylinder Ferrari idling, or the BB in my ProStreet Rod that idles at a lumpy 1000 rpm or what I'd pick, a 4000 hp AA/Fuel Dragster waiting for the green light!




Only 13% of gasoline energy gets to the rear wheels and about 1/3 of that goes back to heat braking!

Last edited by JerryU; 06-18-2017 at 09:55 PM.
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Old 06-13-2017, 03:59 PM
  #23  
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Originally Posted by wmf62 View Post
2016 Tahoe has V4 mode.. the vehicle is so heavy that it hardly ever sees V4 (not only can you see it in the DIC display but you can feel it when it happens...). in this case, an apparent waste of technology and a major annoyance with no apparent real-life benefit...

Bill
The last thing I think about when I buy a Corvette or a truck is gas mileage. I guess I won't be buying anything new. I don't need the drama.
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Old 06-13-2017, 09:34 PM
  #24  
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People actually bog 1st gear enough that skip shift is activated? Lol come on...
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Old 06-14-2017, 07:19 PM
  #25  
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Originally Posted by JerryU View Post
FWIW, the start/stop in the wife's BMW SUV is fine. Can't tell when it starts the minute your foot is off the brake. In fact it also has a variant of energy recovery. They energize the alternator only when costing or braking. Let's most charging occur with otherwise wasted stopping energy!
I have it in both a Jeep GC and Jeep Cherokee, and the worst part about it (if I forget to turn it off), is the 0.3-0.5 second restart time after it shuts itself off while you are stopped waiting to merge into NYC traffic - that 1/2 second is the difference between forcing your way into a merge or waiting up to a couple of minutes until traffic clears enough.
If Jeep stops putting an off switch on the stop/start, I will buy something else.
The real solution for GM is to put the 2.0 turbo in the C7 (like they do in the ATS and Camaro - it does great in the EPA testing, even if in the real world, that 2.0 gets worse fuel mileage (run as hard) as the 3.6L V-6.
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Old 06-15-2017, 08:08 AM
  #26  
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^^^
Don't know about the Jeep system but the BMW does not wait 1/2 second. When you foot comes off the brake, before you have a chance to put your foot on the accelerator, it started.

I also think they must be shutting the engine off with combustion pressure in a cylinder at TDC as I don't hear a starter motor.

Yep I can shut mine off by putting it in Sport but seldom do it's so unobtrusive.

Last edited by JerryU; 06-15-2017 at 08:11 AM.
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Old 06-15-2017, 11:40 AM
  #27  
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Thank God Trump rolled back the future CAFE standards.

The necessity for the undefeatable V4 mode on A8 Corvettes is truly something you can thank Obama for.
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Old 06-15-2017, 02:21 PM
  #28  
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My wife has a 2017 Caddy XT5 with start/stop. I'm not crazy about it, but I've found that it can be by-passed to some degree. Lifting off the brake pedal slightly, before the engine shuts off, will keep the engine running while the vehicle is stopped. It takes a little practice, but it's not difficult to become accustomed to doing.

Originally Posted by wmf62 View Post
2016 Tahoe has V4 mode.. the vehicle is so heavy that it hardly ever sees V4 (not only can you see it in the DIC display but you can feel it when it happens...). in this case, an apparent waste of technology and a major annoyance with no apparent real-life benefit...

Bill
I've had two GM pick-ups with AFM V4, a 2011 Silverado and my current 2016 GMC Sierra. I often see the truck drop into V4 mode, such as at a steady cruise, while idling, etc. My '16 GMC (1500 4x4, SLT crew cab, standard box, 5.3 ltr, 6 speed), regularly averages 20-22 mpg on the highway, and occasionally returns over 24 with the cruise set at 80.

The V4 mode has to be contributing something.
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Old 06-16-2017, 12:59 AM
  #29  
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Originally Posted by gbvette62 View Post
My wife has a 2017 Caddy XT5 with start/stop. I'm not crazy about it, but I've found that it can be by-passed to some degree. Lifting off the brake pedal slightly, before the engine shuts off, will keep the engine running while the vehicle is stopped. It takes a little practice, but it's not difficult to become accustomed to doing.



I've had two GM pick-ups with AFM V4, a 2011 Silverado and my current 2016 GMC Sierra. I often see the truck drop into V4 mode, such as at a steady cruise, while idling, etc. My '16 GMC (1500 4x4, SLT crew cab, standard box, 5.3 ltr, 6 speed), regularly averages 20-22 mpg on the highway, and occasionally returns over 24 with the cruise set at 80.

The V4 mode has to be contributing something.
I could be completely wrong but I would guess AFM does more with larger, heavier trucks. Corvette being a light, aerodynamic car with a powerful engine, I suspect the gas mileage has far more to do with how you drive it (e.g., do you keep your foot in it, or do you stay in high gear / low revs) than AFM.

I don't doubt AFM helps a bit, I just wish they hadn't used the torque converter to dampen vibrations. The A8 issues have me worried enough that I'm willing to give up 1-2mpg to not have to worry about it.

If they had left the TC out of it, and had activated AFM in Eco mode only, I could see myself using it pretty regularly on longer trips. I totally understand Tadge's answer though, fuel regs are what they are.

Last edited by Azmordean; 06-16-2017 at 01:01 AM.
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Old 06-16-2017, 01:08 AM
  #30  
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People are idiots, you do something for their benefit and they bitch and moan about it just because it's "forced" on them. Just like seatbelts, DRLs, airbags, ABS, etc....these things help to save lives but of course there are the morons out there who don't want any of it just because they don't have the option to say "no". AFM is good for the environment and it saves you money, win-win....well you would think it was anyway. I simply just don't understand some people.

IF YOU DON'T WANT AUTOMATIC AFM THEN DON'T BUY AN AUTOMATIC, THERE IS AN OFF SWITCH TO AFM, IT'S CALLED MN7!
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Old 06-16-2017, 02:14 AM
  #31  
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Originally Posted by themonk View Post
People are idiots, you do something for their benefit and they bitch and moan about it just because it's "forced" on them. Just like seatbelts, DRLs, airbags, ABS, etc....these things help to save lives but of course there are the morons out there who don't want any of it just because they don't have the option to say "no". AFM is good for the environment and it saves you money, win-win....well you would think it was anyway. I simply just don't understand some people.

IF YOU DON'T WANT AUTOMATIC AFM THEN DON'T BUY AN AUTOMATIC, THERE IS AN OFF SWITCH TO AFM, IT'S CALLED MN7!
Ummm, have you read nothing about AFM (potentially) causing torque converter failure in A8 cars? Or more specifically, utilizing the TC to dampen vibration potentially causing early failure?

I suspect most people would not complain about AFM (myself included) if there wasn't significant evidence that it contributes to torque converter failure as presently implemented.
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Old 06-16-2017, 10:08 AM
  #32  
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Originally Posted by NSC5 View Post
I understand AFM for fuel economy but I (and probably most owners) if given a choice between keeping the torque converter locked during V4 mode and feeling additional engine vibration (like the M7 owners) or having to deal with multiple very invasive torque converter replacements the choice would be an easy one to make. Or if concerned about customer complaints GM could do like they did with the heated windshield washer fluid issue, disable the modulated lock-up clutch during V4 operation and give the customers a small check for losing the feature. I would be happy to lose the modulated torque converter during V4 mode with no compensation but for PR and legal reasons if GM would feel better about the same $100 check that we got for losing heated washer fluid I expect a huge number of owners would jump on that and it would save the company a lot of warranty costs in trying to overcome this shudder issue.
aaah....so that's where the shudder comes from in the Tahoe....


Bill
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Old 06-16-2017, 10:16 AM
  #33  
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Originally Posted by gbvette62 View Post

I've had two GM pick-ups with AFM V4, a 2011 Silverado and my current 2016 GMC Sierra. I often see the truck drop into V4 mode, such as at a steady cruise, while idling, etc. My '16 GMC (1500 4x4, SLT crew cab, standard box, 5.3 ltr, 6 speed), regularly averages 20-22 mpg on the highway, and occasionally returns over 24 with the cruise set at 80.

The V4 mode has to be contributing something.
not on the Tahoe.... a tad over 19 is the best I have seen (and I drive like I have a raw egg under my foot... )

Bill
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Old 06-16-2017, 02:46 PM
  #34  
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Originally Posted by Azmordean View Post
Ummm, have you read nothing about AFM (potentially) causing torque converter failure in A8 cars? Or more specifically, utilizing the TC to dampen vibration potentially causing early failure?

I suspect most people would not complain about AFM (myself included) if there wasn't significant evidence that it contributes to torque converter failure as presently implemented.
Or how about the tensioner pulley failures that it has caused. (My dealer has replaced several tensioner pulleys because of failures).

Again - we wouldn't be complaining if AFM wasn't causing problems and part to fail prematurely.

And don't say M7 is an option - you don't know everyone's situation and an M7 isn't an option for everyone.
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Old 06-16-2017, 04:33 PM
  #35  
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Originally Posted by Azmordean View Post
Ummm, have you read nothing about AFM (potentially) causing torque converter failure in A8 cars? Or more specifically, utilizing the TC to dampen vibration potentially causing early failure?

I suspect most people would not complain about AFM (myself included) if there wasn't significant evidence that it contributes to torque converter failure as presently implemented.
I've got AFM in the wife's Envoy and can't feel it enter/leave AFM. That old SUV still has a 4L60E. Did they deal with it differently back then or am I on the hook for a torque converter at some point? Either way the trans itself is a matter of when and not if.

What's odd about the alternator pulley failures is that they've been doing the same thing with AC compressors for years without many, if any, issues. Hell the alternator on my 98 GMC pickup is controlled by the PCM. It doesn't have a pulley to engage/disengage but it does have control over commanded amperage which I assume is for economy. Laughable as it gets 13mpg empty and single digits loaded.
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Old 06-18-2017, 12:50 AM
  #36  
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Originally Posted by Corvette4ever View Post
I have a 17 GS "export specs" with A8. Since that we dont have CAFE or EPA here, my car goes V4 only in Eco mode. Doesn't do it in any other mode
The minor annoyance that we have is that it always defaults to Eco mode at startup, which is not the case with US spec cars
The US spec cars are basically in eco mode all the time because we can't turn off eco mode. Your minor annoyance would be awesome for us to have.
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Old 06-18-2017, 12:55 AM
  #37  
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Originally Posted by NSC5 View Post
I understand AFM for fuel economy but I (and probably most owners) if given a choice between keeping the torque converter locked during V4 mode and feeling additional engine vibration (like the M7 owners) or having to deal with multiple very invasive torque converter replacements the choice would be an easy one to make. Or if concerned about customer complaints GM could do like they did with the heated windshield washer fluid issue, disable the modulated lock-up clutch during V4 operation and give the customers a small check for losing the feature. I would be happy to lose the modulated torque converter during V4 mode with no compensation but for PR and legal reasons if GM would feel better about the same $100 check that we got for losing heated washer fluid I expect a huge number of owners would jump on that and it would save the company a lot of warranty costs in trying to overcome this shudder issue.
I wonder if anyone is listening?
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Old 06-18-2017, 08:53 AM
  #38  
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Originally Posted by djnice View Post
The US spec cars are basically in eco mode all the time because we can't turn off eco mode. Your minor annoyance would be awesome for us to have.
I may be wrong but try shutting the car off in any other mode except Track mode. The US models default to either Eco or Tour when you shut it off in Track mode. Try shutting it off in Sport mode and see what happens. There's not much difference in suspension between Track and Sport.
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Old 06-18-2017, 01:20 PM
  #39  
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Yes, it does stay in sport and tour. I was sort of joking since we can't turn off V4 it is as if it were always in eco.
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Old 06-18-2017, 03:43 PM
  #40  
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Originally Posted by Z0SIS View Post
Auto stop/start is a waste for mpg improvements.
80% of vettes are automatics?? WTF.
Cylinder deactivation gives marginal gains at best. Also need to know the long term impacts of only having 4 cylinders running and causing more wear to only half of the top end (this is why Toyota skipped deactivation and is using Atkinson cycle)

Can't GM just produce more fuel sipping A to B cars and then have their way with the Corvette so as to meet the aggregate CAFE standards? Don't get me wrong the Corvette is a fabulous car just seems its being held back.

Thanks for the answers to the original question Tadge.
It's as though you didn't even read his response. Literally, every question you have was answered and every "fact' you asserted without basis was controverted.



My real question for him is why doesn't it stay in 4cyl mode longer. When I'm in 6th or certainly 7th (M7) it doesn't take but a strong headwind for it to go back to 8th. I just hate that change over. Just stay in 4th until I lay into it a bit more.
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