rbweddle

I just bought a used a 2016 Stingray (17,000 miles) and have been reading the Manual I am confused about in what setting the engine shifts from 8 cylinder running and 4 cylinder. I think the manual indicates if you are in Tour, Sport,etc. then only 8 cylinder but in Eco maybe 4 cylinder. I am generally in Tour and when I coast to a stop light, the idle is very quite but I can feel it is not running "smooth" Is this normal?

AmmoVet

Automatic or manual? The only way to keep the auto out of 4 is to run in manual and use the paddles. With a manual trans the only way it will go into 4 is when your in eco mode.

Bill Dearborn

The idle can be a little rough since it is a V8 with a performance cam.

Bill

rbweddle

I have auto.

davepl

As Bill noted, the slightly lumpy idle is the nature of the performance cam in this motor. But rest assured it's not related to V4/C8 operation.

You'll only see V4 when cruising on flat or a decline plane roadway at higher speeds, basically where the motor isn't working at -all-, it'll switch to V4. Like at 60mph with cruise on when you start to go slightly downhill, that's when you'd see it.

As far as I know with the Auto it'll happen in any mode, whereas with the stick you must be in Eco, I think. If you're on the economy screen you can see the V4/V7 indicator on the dash display.

rbweddle

Thanks all. A lot of changes since my 1985 C4.

tblu92

Any GM car with AFM will never run on 4 cylinders at idle---and never in a gear lower than 3rd--so this is not why you may be experiencing a not so smooth idle----In order for AFM to be activated / de-activated it takes multiple parameters to be met----

Speed
RPM
Current gear
Manifold vacuum

CP

Bill Dearborn

Hey, V7 mode contributes to the lumpy idle. If you want your car to sound mean at the local cruise in just pull a spark plug cable. You get the same affect as a really mean cam and it doesn't cost you anything except some extra gasoline.

Bill

767guy

Congrats on your new American Icon. Welcome to the forum.

If you want to monitor when the engine is running in V8 or V4 mode you can display this information on your DIC, see the owners manual.

For the A8 transmission it is possible to be in V4 mode when the shift selector is in "D" and in any of the drive settings ECO, WEATHER, TOUR , SPORT , TRACK. However the following is a short list of some of the conditions that are required , in addition to the above, for the engine to switch into V4 mode;
*engine running more than 30 seconds
*engine speed between 700 and 2800RPM
*oil pressure 27-66 psi
*oil temp 61-263 degrees F
*coolant temp 100-263 degrees F
* throttle angle 6% or less
*vehicle speed greater than aprox 15 MPH
*Transmission must be in fourth gear or higher
The list goes on but those are the parameters the driver can see.

The transition to V4 mode occurs in 250 milliseconds and always
shuts down the same cylinders,1&7 on the left bank ,6&4 on the right bank. In V4 mode the engine is inherently rough so the Torque Tube, Torque converter and other components are designed to smooth things out. You will see posts on the forum from members that have " rough " drive line issues which frequently is a result of these components not working correctly.

Lots of good stuff to learn about our C7's from the forum members so congrats again on your ride and if you get a chance post some pix

I just assumed you have an A8 so if you have a M7 sorry to have caused your eyes to glaze over

CP

Which do you think resulted in a larger cost to the buyer: All the AFM hardware and software needed to run it or the gas guzzler tax? I'm opting for the former, personally.

767guy

^^^^^^^^^^^^^^

NSC5

Well Dave's V7 typo may not be so far fetched since at least two different concerns are designing systems that can drop any number of cylinders and cycle through the different cylinders to equalize wear over time. Some of the Japanese automakers earlier expressed concern that consistently shutting off the same cylinders will result in unequal wear which will become noticeable as the engine operating hours add up. Delphi had an announcement about their proposed system sometime last year. Maybe it is time to buy stock in firms that are designing isolating mounts for the engines and drivetrain to handle the NVH from these "AFM on steroids" systems of the future.

rbweddle

Yep, got the A8. Definitely looks like running in V4 not a concern. I also have an Audi A8L I am fortunate, best sedan in the world and best sports car

KemahGT

I would gladly pay the tax to avoid AFM. However, Chevy probably doesn't have a choice. Gotta please those tree hugging folks that rammed CAFE down everyone's throats.

spireland

I drive a ton, so I'm glad CAFE standards got rammed down everyone's throats.

I'll take my AFM and V4 mode.

KemahGT

And you can have my TC problems, and AFM. I'll send you all of the parts when I'm done. You're gonna need them.

spireland

Lol. Someone's salty.

TwoVettes6916

I appreciate the cylinder management system - I have it on three of my vehicles. I do a combination of town/highway, flat/hilly driving and, as long as my foot doesn't become too heavy on the gas pedal, I get almost as good mileage from my Vette as from my 6-cylinder Honda (sorry forum members) Accord (28 Accord/ 26 Vette). Interesting situation, since, even with four cylinders deactivated, I still have 230 ponies to pull me along as compared to 267 in the Accord with all 6 cylinders firing.

Similar situation with my Sierra, although the most I have ever been able to get out of it has been about 22 mpg - maybe because I use it for light hauling sometimes.

I love all of this technology!

davepl

Second best... I have the S8 :-)

Too bad deactivating half of its cylinders would leave you with 5!

I have no problem with AFM. Worst case I think I might have once though I heard a rumbling sound when it kicked it. I wouldn't take the cost and complexity by choice but I think GM has done a good job with it.