Looks like I'm experiencing the "not so uncommon" issue where the vehicle shudders under particular circumstances.

2022 Stingray Z51 and just crossed 10k miles on the OD ...

1st time I noticed it, I honestly thought the road had washboard pavement on it. Going down the highway, steady state, and just applying throttle to maintain 70mph or so, while going up a slight incline. This is the most common symptom I experience, and have been for the last 2k miles or so.

Another symptom was accelerating up a fairly steep hill on a 65mph road. I was accelerating from a stop, getting up to speed, with about 50% throttle pedal engaged. Then suddenly, the vehicle increased acceleration even though I was holding the throttle steady (and going up hill). The best way to describe this is like I was pulling a trailer with extra weight, and then suddenly the rope was cut releasing the weight.

The latest symptom is the same shuddering feeling I get on the highway, but it's now happening at much slower speeds. Still with light throttle application, but it can now make the vehicle buck and shake back and forth.

My initial thought was DCT, but now I don't think so. I'm thinking it is either the "lose spark plug wire" issue, or is the "sticking camshaft actuator magnet" issue.

Before I pull the engine sheer plate and check the plug wires, I figure I will hook up my HP Tuner's laptop and capture a log with the cam position sensor data. According to TSB 22-NA-080 (PDF attached to this post), the Camshaft Position Variance parameter should never exceed 4% variance. So if I can log this parameter with VCM Scanner, I should be able to confirm or rule out this as the cause. If the variance is 4% or less on a test drive where the shudder happens ... then I'll pull the sheer plate and check the plug wires.

 

Good Luck and please post what you find. I see several people on C8 FB pages have this issue.

 

So I pulled a few logs, and the shudder did not happen while logging. Checking the data, the cam position looks good (variance never went above 2.2*), so well under the 4* threshold the TSB calls out. I do see some random misfires here and there, but HP Tuners can often report misfires even when not real misfire activity. And since it's reporting them when I'm not feeling the shudder, I'm not sure that's the cause.

What I do find interesting is that I had to unplug the Carbyte AFM disabler in order to plug in my MPVI3 interface, so I could take logs with HP Tuner's VCM Scanner software. So I wonder if the methodology the Carbyte disabler uses is flooding the canbus with info, to trick the PCM into keeping V4 mode off, and this approach is causing a torque model fluctuation. I'll leave the Carbyte AFM disabler unplugged for the next week or so, and see if the issue comes back. If it doesn't , then I'll reinstall the Carbyte device and test again.

 

Feeling shuddering while driving your Corvette is absolutely not part of the ownership experience we hope to hear from any of our owners. Safety is a top priority for us and we take matters like this very seriously. We want to ensure this shuddering gets addressed as soon as possible alongside your dealership. Please visit https://s.chevy.com/support-request and fill out our support form with additional details so our team can get in contact as soon as possible. We will look out for your contact.

 

Thanks, my power train warranty is good until Sep of this year, and I also have a platinum Chevy Protection Plan extending beyond. But honestly, I trust my own diagnoses skills more than my local dealer, so will try to diagnose this myself before bringing it in (if it needs to be brought in).

If I end needing a warranty repair, I'll definitely fill out the support form before doing so.

 

Always interesting to me that on nearly every car forum of which a member, someone plugs in a tune, or gizmo, and then the car misbehaves. The owner then comes on the forum and asks advice on how to fix a problem that they most likely are the source.

Modern cars are complicated computers on wheels and one never knows what will affect what in the programming.

To the OP, Good Luck sorting, but start as you have, by unplugging every device you have installed, and go from there.

 

Yeah. The CarByte doesn't (can't) change the programming, but it sure can and obviously does interfere with the information exchange on the network. ( say obvious because it prevents V4). And nobody knows how it accomplishes that. It very likely monitors certain data exchanges, probably using hooks that are available to scan tools (in fact it will even function as a "full-featured" scan tool ), and then it must be injecting info, either via available scan tool hooks or something else. Its either preventing the command to enter V4 mode, or maybe preventing the car from responding to the command. But it prevents the activation of the evil, insidious, and much dreaded V4 mode. So there is that. I don't have one.

It will be interesting to see if unplugging it stopped the issue.

 

Yes, there are a ton of folks out there who have no idea how a modern car works ... luckily, I'm not one of them

There are a couple of standard methodologies companies use to accomplish things like what the Carbyte is doing. I'ce spent enough time snooping canbus networks on modern cars to understand what is happening here. The Carbyte is flooding the network with a particular canbus message to trick an ECM in the system into thinking a parameter is at such a range where V4 mode is not allowed. I'm not sure which parameter it is flooding, but if it's one which is used to modify the torque model when in V4 mode, then I can see how it could cause a torque model oscillation.

I do have a DLC (diagnostic link connector) snooping cable (ie: an OBD-II snooping cable), which I made when I was reverse engineering the canbus network on my wife's Durango. That said, I really don't have a desire to go to that depth here and will just leave the Carbyte out if it is in fact the cause. If it's not though, I'll probabyl plug it back in.

 

I do have a carbyte and I have not experienced an issue specific to it. I did experience 'hick ups' or shudder at low rpm (1250-1475) when going uphill at low throttle (10% like feathering the pedal) before carbyte was installed, this is almost exclusive to V4 mode. At the same time I also hear brief 'chatter/rattle' from the rear of the car.

 

No carbyte, and never had the shudder. Not rattle or chatter. 2021. When leisurely cruising back roads with short stretches of hills up and down and curves, with engine/shift set to Tour, I find that the car will frequently transition between V4 and V8. I don't feel a shudder or hear any noise from the the muffler valves - and I use the Track theme DIC so I never see the V4 indicator. But I do sense the change in the exhaust note and the change in the feel or powertrain (some do and some don't), and I don't care for it. So, in that driving scenario I use manual shift mode. I prefer that anyway - I do not like the automatic gear selection in any setting of engine/shift for that situation. For highway cruising or higher speed cruising, I really never notice the transition at all.

That said, I have seen other reports of some less than perfect V8-V4 transitions, so you are not the only one.

 

Sometimes if I am going uphill at light throttle when V4 mode activates, I can feel a slight interruption or hiccup in the acceleration. It's pretty rare.

The only "shudder" I've experienced is when I let off the gas abruptly at low RPM, especially in manual mode, I feel a vibration for a brief moment. Dealer told me it's normal and that other C8s do it. Under throttle, there is no such issue - only when releasing.

 

Is this your theory, or have actually used a sniffer of some sort and observed that is "flooding the network" with a message? In other words, how do you know this? I'm not picking at you, I'm really interested in how it works.

 

I would add a can of Sea Foam or Techron to it before doing anything else.
Cheap, easy, non invasive, and quick and your engine probably needs it anyways !

 

If you are truly interested in how it works, this is a good read for you:

https://munich.dissec.to/kb/chapters...elattacks.html

it does a good job of explaining the different methods available for attacking a canbus network.

I have snooped a lot of canbus, and have built my own microcontrollers to flood and also to perform Can Frame Tampering through “man in the middle” approach, by injecting my controller into the hardware directly (not adding a flooding source, but chaging existing messages while they are en-route); So all messages to and from a specific ECU would have to pass through my controller.

The Carbyte cannot do man in the middle though, as it plugs into the DLC connector, and only works while it is plugged in. It’s most definitely flooding the network with fake messages. This is an extremely common and cheap way to do this sort of thing.

zAutomotove does the same thing for some of its functions with their Tazer device for Stellantis vehicles.

 

Since removing the Carbyte, I’ve put about 100 miles on it, and haven’t experienced the issue since. I’ll drive it all this week to be sure, but it’s looking like the issue was related to the Carbyte device.

It was presenting itself in scenarios when V4 mode should have been enabled, but was being blocked by the Carbyte. This is what is making me think it’s most likely related to torque oscillation …. Probably due to conflicting canbus messages.