Intermittent missing
Thread Starter
3rd Gear
Joined: Mar 2017
Posts: 3
Likes: 0
From: Horseshoe Bay Texas
Intermittent missing
Just wondering if anyone else is seeing this. I have a 2015 2LT with just under 16k miles. I have noticed that when driving 70 mph and in V4 mode, it seems like it has an intermittent cylinder drop. You can feel a small shudder and the tach drops about 100 rpms and then returns. I just started noticing this and took is to my local dealer. They couldn't find anything and the mechanic took another Corvette from their stock and says it does the same thing. It does it in V8 mode too but it isn't as noticeable. I think something is wrong since I didn't notice it in the last 15k miles but they say it is normal since I didn't get a engine light.
Burning Brakes
Joined: Jan 2011
Posts: 825
Likes: 99
Is this an auto? If so try using the paddles to select a gear and see if it still does it. Could be in too high of gear for the road, perhaps an incline etc and it's bogging in v4. That does not explain why it occurs in V8 though.
Thread Starter
3rd Gear
Joined: Mar 2017
Posts: 3
Likes: 0
From: Horseshoe Bay Texas
It is an auto but I'm traveling at 70mph in cruise control with tach running 1500 rpm in V4 mode. The road is flat and you can feel the change kinda like when it goes from V4 to V8. You can see the tach dip from 1500 to 1400 and back. A few seconds later it will do it again. Showed the service manager but he tried to say it was the way I was feathering the accelerator but I put it in cruise to prove it wasn't my foot doing it.
Safety Car
Joined: Aug 2012
Posts: 3,960
Likes: 1,106
V4 operation and the strategy of "modulating" the A8 converter lock up clutch to absorb V4 mode vibration is a bad combination. My Z06 A8 will be staying in manual mode to avoid V4 operation and subsequent problems with the torque converter clutch wear.
Dazed Confused & Verklemp
Joined: May 2008
Posts: 1,397
Likes: 106
From: Naples, FL & Clear Lake, IA
You are correct that one has to be in "M" mode to keep an A8 from going into V4 mode in all drive modes.
The problem with keeping your A8 in manual mode is that you have to shift after coming to stop, or switch to "D" until back to cruising speed etc.
This should be a simple fix, in that it is easy to have your ECM programmed to stay out of V4. Unfortunately, this voids the GM warranty. Also, not sure if the Torque Converter issue will get increasingly worse over time.
Mine was replaced at around 9K. Took almost a week. Hendrick Chevy in Naples did a very good job... No issues.... YET.. Was told that it is a 22-24 hr job + parts and fluids, which makes it about a $3,000. repair cost to GM, so obviously is a serious issue.
Very happy with current driveability of my 2015 Z51 A8. Loved it before fix and love it more after.
Just hoping there aren't other issues with A8. But... if there are, hope they occur before 5 yr anniversary, or require an A8 wide recall. Would like to know the actual percentage of A8 problems, rather than GM's statements.
The problem with keeping your A8 in manual mode is that you have to shift after coming to stop, or switch to "D" until back to cruising speed etc.
This should be a simple fix, in that it is easy to have your ECM programmed to stay out of V4. Unfortunately, this voids the GM warranty. Also, not sure if the Torque Converter issue will get increasingly worse over time.
Mine was replaced at around 9K. Took almost a week. Hendrick Chevy in Naples did a very good job... No issues.... YET.. Was told that it is a 22-24 hr job + parts and fluids, which makes it about a $3,000. repair cost to GM, so obviously is a serious issue.
Very happy with current driveability of my 2015 Z51 A8. Loved it before fix and love it more after.
Just hoping there aren't other issues with A8. But... if there are, hope they occur before 5 yr anniversary, or require an A8 wide recall. Would like to know the actual percentage of A8 problems, rather than GM's statements.
Safety Car
Joined: Aug 2012
Posts: 3,960
Likes: 1,106
Bob,
The Range AFM module will keep it in V8 mode but a few times last year it created errors at startup. I am sending mine in for an update although a few people still report intermittent issues with the current version. AFM mode doesn't happen nearly as often in my Z06 but it will still go into V4 mode when coasting and presumably under the right conditions during highway cruising although the only time seems to be on a descending grade. These days I just leave the transmission set to manual mode. Since there are already reports of 2017 GS models with the shuddering issue I am afraid they still don't have the torque converter clutch issue resolved.
The Range AFM module will keep it in V8 mode but a few times last year it created errors at startup. I am sending mine in for an update although a few people still report intermittent issues with the current version. AFM mode doesn't happen nearly as often in my Z06 but it will still go into V4 mode when coasting and presumably under the right conditions during highway cruising although the only time seems to be on a descending grade. These days I just leave the transmission set to manual mode. Since there are already reports of 2017 GS models with the shuddering issue I am afraid they still don't have the torque converter clutch issue resolved.
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