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As long as the car stays under 1500 rpm (in 5th gear) and has a slight load like going uphill. What I am noticing though is that mine may have gone away now that we are in summer conditions again.
I bought the car in May 2023. I had no lugging. Lugging started sometime in late fall/winter when the temperatures dropped. It seems that now with warm temperatures being back, lugging has gone away again.
Maybe GM algorithm does not take temperature (or the effects of temperature) under account or it could be the fuel. In the northeast they switch to 'winter blend' at some point and then back to normal again. The octane rating does not change though, I use 93.
The algorithm takes into account torque output, so it makes sense that the engine performance is going to vary from winter to summer because of DA and different fuel blends as you mentioned. You seem to be very sensitive to the engine which is a good thing, but every scenario can’t be accounted for and I’d figure out away to drive around it. I didn’t like the transmission programming of the 10-speed in my 5.0 F150 that didn’t have cylinder deactivation, but had 12:1 compression and because it would skip gears it’d lug at times depending on the inputs of my right foot. Some of the programming I believe is to satisfy EPA and lower the emissions outputs in certain conditions for testing certification purposes, though could be wrong.
So, we have lugging, knocking, and chirping. What is chirping? Mine sometimes makes what I would call a chirp as it transitions between modes, but not always. I think it is the sound of exhaust flow control valves in the muffler opening or closing - they occasionally squeak. I can sometimes hear them squeak just sitting and change the engine sound setting. And some hear a "swoosh" perhaps like air, but only at transition. I don't know where that one comes from. Some say its from actual transition of the valve train. I think it might be just exhaust gas rushing past the valves as they close, but I do not know. Are you hearing something else - a different sound?
If I am on a very very slight incline in AFM mode, I can sense that feel that is reminiscent of lugging (low rumble) but it is very subtle, not pronounced at all and could easily go unnoticed. It is nowhere near the actual sensation of lugging from yesteryear. And no knock. Anything more pronounced should not be evident - its designed to be seamless - and many/most say it is. Any more than very very slight incline or even just slight increase in throttle angle and it will pop out of the V4 mode.
I would say it sounds like a more subtle ping. It always coincides with the low rumple. I don't know if you remember old cd/dvd drives, everytime you'd put a new disc in it would 'seek' and it would make a chirping noise as the stepper motors moved things around in there. That's what it sounds like and it's very unnerving for anyone who's on the lookout for actual pinging.
I would say it sounds like a more subtle ping. It always coincides with the low rumple. I don't know if you remember old cd/dvd drives, everytime you'd put a new disc in it would 'seek' and it would make a chirping noise as the stepper motors moved things around in there. That's what it sounds like and it's very unnerving for anyone who's on the lookout for actual pinging.
I’ve never heard detonation described as chirping, more like marbles in a can.
But it doesn't mention AFM but the common thing is timing retardation which is what mine feels like based on the womp womp womp noise.
The first one appears to be related to AFM and the issue is body or catalytic converter mounts. I think this applies to a body on frame design and the C8 is very different. There are vibrations that are associated with AFM - that are normally well controlled - but its possible I suppose that that something is "loose" and amplifying the sound.
The second refers to noise that happens at transient events (brief/short) that involve a very brief reduction in timing advance (cold start (30 sec), Engine Restart (1 sec), Auto-Start (1 scec), Throttle Blip in Park or Neutral. And, in fact, I have noticed a quick, and light knock on my other vehicles in these very conditions but not on C8. I don't think this one is relevant.
Your sound is happening during steady cruising when the car is in AFM. As you probably know, AFM closes the valves on 4 of the 8 cylinder capturing a combustion charge in each, and shuts off fuel to those cylinders, so they act as springs, presenting very little loss. The remaining cylinders must produce the same power as the 8 previously did, but they can do it more efficiently. The throttle plate actually opens slightly more (see descriptions below from Tadge and a technical paper) which reduces the pumping loss. I do not know what happens to timing during V4 mode but I suspect it requires adjustment (my guess is slightly pulled but I do not know) since the there is a higher load on the 4 active cylinders. But we are talking about very, very light loads - it only takes around 40 hp or less during the steady cruising where AFM is active (see Tadge remarks below) - so that is 5hp/cyl in V8 mode and 10hp/cyl in V4 mode. Nowhere near the engine capability. None of this really explains what you are hearing though.
From Tadge:
" It only takes 12 - 40 HP (depending on model and speed) to push a Corvette down a flat road at highway speeds. Producing that small amount of horsepower with all 8 cylinders firing and then practically closing the throttle is not as efficient as running on 4 cylinders with the throttle blade more open. " "Our AFM system is very effective on the small block V8. It lets us close the valves on the de-activated cylinders so the cylinders act as air springs. When the engine rotates we get energy back as the compressed air in the cylinder expands. Other manufacturers just stop fueling the de-activated cylinders and so don't get much fuel savings. The reason 4-cylinder operation is more efficient is that the active cylinders are worked harder with a greater throttle opening. That's like taking a restrictor out of the system saving pumping losses."
From a Technical Document:
"In order to deactivate a cylinder, the intake and exhaust valves are held closed. This creates an “air spring” in the combustion chamber, in which the preceding cycle’s exhaust gases are trapped and compressed in the upstroke and expanded in the downstroke. This compression and expansion result in reduced engine friction losses for the deactivated cylinders. In cylinder deactivation systems, the engine management system stops fuel from being delivered to the deactivated cylinders. Ignition and cam timing, as well as throttle position, are adjusted to ensure that switching from full cylinder operation to cylinder deactivation is nearly imperceptible. Until recently, cylinder deactivation primarily has been employed in engines with high displacement, which have low efficiency at light loads."
National Academies of Sciences, Engineering, and Medicine. 2015. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, DC: The National Academies Press. https://doi.org/10.17226/21744.
The first one appears to be related to AFM and the issue is body or catalytic converter mounts. I think this applies to a body on frame design and the C8 is very different. There are vibrations that are associated with AFM - that are normally well controlled - but its possible I suppose that that something is "loose" and amplifying the sound.
The second refers to noise that happens at transient events (brief/short) that involve a very brief reduction in timing advance (cold start (30 sec), Engine Restart (1 sec), Auto-Start (1 scec), Throttle Blip in Park or Neutral. And, in fact, I have noticed a quick, and light knock on my other vehicles in these very conditions but not on C8. I don't think this one is relevant.
Your sound is happening during steady cruising when the car is in AFM. As you probably know, AFM closes the valves on 4 of the 8 cylinder capturing a combustion charge in each, and shuts off fuel to those cylinders, so they act as springs, presenting very little loss. The remaining cylinders must produce the same power as the 8 previously did, but they can do it more efficiently. The throttle plate actually opens slightly more (see descriptions below from Tadge and a technical paper) which reduces the pumping loss. I do not know what happens to timing during V4 mode but I suspect it requires adjustment (my guess is slightly pulled but I do not know) since the there is a higher load on the 4 active cylinders. But we are talking about very, very light loads - it only takes around 40 hp or less during the steady cruising where AFM is active (see Tadge remarks below) - so that is 5hp/cyl in V8 mode and 10hp/cyl in V4 mode. Nowhere near the engine capability. None of this really explains what you are hearing though.
From Tadge:
" It only takes 12 - 40 HP (depending on model and speed) to push a Corvette down a flat road at highway speeds. Producing that small amount of horsepower with all 8 cylinders firing and then practically closing the throttle is not as efficient as running on 4 cylinders with the throttle blade more open. " "Our AFM system is very effective on the small block V8. It lets us close the valves on the de-activated cylinders so the cylinders act as air springs. When the engine rotates we get energy back as the compressed air in the cylinder expands. Other manufacturers just stop fueling the de-activated cylinders and so don't get much fuel savings. The reason 4-cylinder operation is more efficient is that the active cylinders are worked harder with a greater throttle opening. That's like taking a restrictor out of the system saving pumping losses."
From a Technical Document:
"In order to deactivate a cylinder, the intake and exhaust valves are held closed. This creates an “air spring” in the combustion chamber, in which the preceding cycle’s exhaust gases are trapped and compressed in the upstroke and expanded in the downstroke. This compression and expansion result in reduced engine friction losses for the deactivated cylinders. In cylinder deactivation systems, the engine management system stops fuel from being delivered to the deactivated cylinders. Ignition and cam timing, as well as throttle position, are adjusted to ensure that switching from full cylinder operation to cylinder deactivation is nearly imperceptible. Until recently, cylinder deactivation primarily has been employed in engines with high displacement, which have low efficiency at light loads."
National Academies of Sciences, Engineering, and Medicine. 2015. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, DC: The National Academies Press. https://doi.org/10.17226/21744.
Highway drive today, 7th gear drops to ~60mph in AFM mode. Continuous chirping, 8th gear ~68-70mph in AFM mode, continuous chirping. Seems to be related to rpm < 1500.
Highway drive today, 7th gear drops to ~60mph in AFM mode. Continuous chirping, 8th gear ~68-70mph in AFM mode, continuous chirping. Seems to be related to rpm < 1500.
I got nuthin' else to offer. Have the dealer listen to it if you can. Or drive or ride in another one and see it is the same. I don't notice anything other than the very low subtle rumble, and most report not even noticing that. You may have an issue. I'll be driving mine today - I'll listen for it.
To be clear the AFM is very seamless except when this particular load condition occurs. And it doesn't happen at 1000rpm... It happens somewhere around 1,250 rpm under light load in V4 mode.
Occasionally I hear the AFM valves close but that's not what I'm talking about.
To be clear the AFM is very seamless except when this particular load condition occurs. And it doesn't happen at 1000rpm... It happens somewhere around 1,250 rpm under light load in V4 mode.
Occasionally I hear the AFM valves close but that's not what I'm talking about.
OK. Doubled checked today. First a highway ride at 60-65. I tried to get into the RPM range you mention. Top up. Tour mode. I normally use the Track Mode display theme for all Drive Modes, but for the test I changed to the Tour Mode display theme so I could watch the AFM icon. So...I could detect absolutely nothing within the limits of my perception. No rumble, not chirp, no knock, not even the transition. At highway speed. And on long flats and on slight inclines. Much more incline and it transitions out but I feel nothing when that happens.
So then I tried leisurely drive on the back roads with stretches of flats, mild inclines. Again trying to keep rpm in the range you mentioned. About the only thing I could detect is what I mentioned before - on a slight incline there is a slight sensation or sound of a low rumble, very subtle, with no chirp, ping, or squeak. Any more of an incline and I briefly hear that sound before it transitions smoothly to V8 mode.
If you are hearing more than that, you may have an issue.
OK. Doubled checked today. First a highway ride at 60-65. I tried to get into the RPM range you mention. Top up. Tour mode. I normally use the Track Mode display theme for all Drive Modes, but for the test I changed to the Tour Mode display theme so I could watch the AFM icon. So...I could detect absolutely nothing within the limits of my perception. No rumble, not chirp, no knock, not even the transition. At highway speed. And on long flats and on slight inclines. Much more incline and it transitions out but I feel nothing when that happens.
So then I tried leisurely drive on the back roads with stretches of flats, mild inclines. Again trying to keep rpm in the range you mentioned. About the only thing I could detect is what I mentioned before - on a slight incline there is a slight sensation or sound of a low rumble, very subtle, with no chirp, ping, or squeak. Any more of an incline and I briefly hear that sound before it transitions smoothly to V8 mode.
If you are hearing more than that, you may have an issue.
Obviously, our cars are behaving differently than yours
Not trying to be a wise guy or anything, but for you guys having this issue, do you drive like an old lady coming home from church? Or do you dive like a horny 18yr old late for a date?
Sometimes a little carbon in the cylinders can raise heck with high performance engines.
I would advise driving it hard for a bit. Full throttle runs where safe to blow the crap out of it, then see how it acts after.
Not trying to be a wise guy or anything, but for you guys having this issue, do you drive like an old lady coming home from church? Or do you dive like a horny 18yr old late for a date?
Sometimes a little carbon in the cylinders can raise heck with high performance engines.
I would advise driving it hard for a bit. Full throttle runs where safe to blow the crap out of it, then see how it acts after.
Car has 2,500 miles on it and has been doing it for some time. So it's not carbon build up.
Car has 2,500 miles on it and has been doing it for some time. So it's not carbon build up.
Odometer doesn't tell HOW it's driven. I'd love to pull a spark plug or 2, they'll tell ya.
Give it a few 0-60 runs. Put that pedal to the floor every now and then and use top tier gasoline while doing it. Your engine will reward you.
Odometer doesn't tell HOW it's driven. I'd love to pull a spark plug or 2, they'll tell ya.
Give it a few 0-60 runs. Put that pedal to the floor every now and then and use top tier gasoline while doing it. Your engine will reward you.
Can't avoid it. Lots of traffic and lights where I live. When I do get the opportunity I do let go. I just posted yesterday that I drove it hard (really hard) and then there was no more chirping. No way I can drive it like that all the time, it's just not safe or legal on public roads.
Not trying to be a wise guy or anything, but for you guys having this issue, do you drive like an old lady coming home from church? Or do you dive like a horny 18yr old late for a date?
Sometimes a little carbon in the cylinders can raise heck with high performance engines.
I would advise driving it hard for a bit. Full throttle runs where safe to blow the crap out of it, then see how it acts after.
Think of it this way, you have 490-495 horses, If you don't let out all the horses for a good run every now and then, some of your horses will get fat, lazy and might even die.
Only from experience with old time engines would I have known it - if it is accurate. GM made the following statement to Corvette Action Center, but note it only refers to spark plug fouling that might result from not letting the car fully warm up and it says spirited driving may prevent carbon build up and clean partially impacted plugs. I think most of us already know we should not make frequent runs that do not even allow the car to fully warm up. But the notice was not about carbon build up in general. I suppose its reasonable to assume that if carbon from combustion can build up on the spark plugs, it can also build up on other parts of the combustion chamber. My father told me that some 60+/- years ago!
Only from experience with old time engines would I have known it - if it is accurate. GM made the following statement to Corvette Action Center, but note it only refers to spark plug fouling that might result from not letting the car fully warm up and it says spirited driving may prevent carbon build up and clean partially impacted plugs. I think most of us already know we should not make frequent runs that do not even allow the car to fully warm up. But the notice was not about carbon build up in general. I suppose its reasonable to assume that if carbon from combustion can build up on the spark plugs, it can also build up on other parts of the combustion chamber. My father told me that some 60+/- years ago!
Would it happen within 1500 miles of driving it since new. That's when it started.
on public roads.
