[ANSWERED] Why can you not just disable the AFM?
06-12-2017, 02:47 PM
#21
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.
Last edited by NSC5; 06-12-2017 at 02:48 PM.
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djnice (06-17-2017)
06-12-2017, 04:07 PM
#22
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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?
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 08:55 PM.
06-13-2017, 02:59 PM
#23
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St. Jude Donor '09-'10-'11-12-'13-'14-'15-'16-'17-‘18-'19-'20-'21-'22-'23
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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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Maxie2U (06-30-2017)
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Claude130 (12-01-2021)
06-14-2017, 06:19 PM
#25
Melting Slicks
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!
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.
06-15-2017, 07:08 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.
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 07:11 AM.
06-15-2017, 10:40 AM
#27
Melting Slicks
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.
The necessity for the undefeatable V4 mode on A8 Corvettes is truly something you can thank Obama for.
06-15-2017, 01:21 PM
#28
Race Director
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.
The V4 mode has to be contributing something.
06-15-2017, 11:59 PM
#29
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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.
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'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 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 12:01 AM.
06-16-2017, 12:08 AM
#30
Team Owner
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!
IF YOU DON'T WANT AUTOMATIC AFM THEN DON'T BUY AN AUTOMATIC, THERE IS AN OFF SWITCH TO AFM, IT'S CALLED MN7!
06-16-2017, 01:14 AM
#31
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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!
IF YOU DON'T WANT AUTOMATIC AFM THEN DON'T BUY AN AUTOMATIC, THERE IS AN OFF SWITCH TO AFM, IT'S CALLED MN7!
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.
06-16-2017, 09:08 AM
#32
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St. Jude Donor '07
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.
Bill
06-16-2017, 09:16 AM
#33
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St. Jude Donor '07
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.
)Bill
06-16-2017, 01:46 PM
#34
Instructor
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 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.
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.
06-16-2017, 03:33 PM
#35
Safety Car
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 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.
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.
06-17-2017, 11:50 PM
#36
Melting Slicks
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 minor annoyance that we have is that it always defaults to Eco mode at startup, which is not the case with US spec cars
06-17-2017, 11:55 PM
#37
Melting Slicks
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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Maxie2U (06-30-2017)
06-18-2017, 07:53 AM
#38
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.
06-18-2017, 12:20 PM
#39
Melting Slicks
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.
06-18-2017, 02:43 PM
#40
Le Mans Master
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.
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.
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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Maxie2U (06-30-2017)
