Cylinder on demand (c7 performance)

Rs3Life

Registered User
Hi all,

I'm new to rs6 and the cylinder on demand technology so I just want to check if all is good with the car or I should ask Audi to investigate the potential issue.

Over the weekend I did 400 miles on highways and I was able to notice slight move or shake (similar to going over small bump or while downshift) when the car was turning off the 'cylinder on demand' mode and going back to full v8 mode. It does make sense as the half of engine will start again but I just want to make sure that's not a indication of some issue.

Thanks in advance :audibash:
 

Jcbmally

Started with nothing & still have most of it left.

Hi all,

I'm new to rs6 and the cylinder on demand technology so I just want to check if all is good with the car or I should ask Audi to investigate the potential issue.

Over the weekend I did 400 miles on highways and I was able to notice slight move or shake (similar to going over small bump or while downshift) when the car was turning off the 'cylinder on demand' mode and going back to full v8 mode. It does make sense as the half of engine will start again but I just want to make sure that's not a indication of some issue.

Thanks in advance :audibash:
Supposed to be seamless so a knock etc is not normal IMO.
The 4 cylinder Audi blurb below and link to the V8 below that, but basically states the same.

The switching process takes just milliseconds, and the driver virtually does not even notice it. In the active cylinders one and four, the operating points shift to higher load, which boosts efficiency, while the deactivated cylinders follow – essentially with no losses – like compressed gas springs at low pressure. When the driver presses the accelerator pedal, the deactivated cylinders are reactivated.

V8 COD engines
 

RAF_S7

Well-Known Member
Gold Supporter
The COD tech also makes use of the active engine mounts when changing from 8 to 4 cylinder mode, to stop exactly any sensation of switching modes.

Are you able to scan using VCDS to see if there are fault Codes?

Engine mounts are a known weakness across all of the 4.0T model range, so definitely worth having checked. It’s also not a cheap repair, with the mount itself around the £600 mark :racer:
 

Rs3Life

Registered User
The COD tech also makes use of the active engine mounts when changing from 8 to 4 cylinder mode, to stop exactly any sensation of switching modes.

Are you able to scan using VCDS to see if there are fault Codes?

Engine mounts are a known weakness across all of the 4.0T model range, so definitely worth having checked. It’s also not a cheap repair, with the mount itself around the £600 mark :racer:
Don't have device to scan myself. I do have the Warranty from manufacturer for 1 year (Audi approved used) so I will have a little play on highway and ask them to investigate.

Tbh that knock/push is not something I would notice as passenger but I'm over sensitive as driver. If Audi will say that all is good then I will go to a private garage for investigation of the issue.
 

Rs3Life

Registered User
Little update.

I didn't get car to garage yet as they looking for some space (hopefully they will take it on Monday) but I noticed some other symptoms.

1. While changing from Parking mode to Drive or Reverse after a second I feel a slight pull. (Car is not in auto brake or with handbrake on as I'm on flat drive). I did the procedure for ECU reset (not sure if that works on C7) but it's still happening.
2. I did few tests with different modes and gears but 3rd gear had biggest difference so I will focus on that (Gearbox in Manual):
  1. Gearbox in D - Stuck in 3rd gear - accelerate to 50, release gas pedal, drive 5 seconds until the car drops revs and disconnects fuel supply then slowly start pressing gas pedal - I was able to feel slight pull/jerk while accelerating or deceleration (Feels similar to the pull on drive mode change).
  2. Gearbox in S - Stuck in 3rd gear - accelerate to 50, release gas pedal, drive 5 seconds until the car drops revs and disconnects fuel supply then slowly start pressing gas pedal - I'm able to feel stronger pull/jerk while slow deceleration. Feels like the car at around 2-3% of throttle disconnects the drive to make the nice pop and bangs (as that's the only difference between D and S that I noticed). Then on acceleration I need to press that extra 2-3% before the car pulls and obviously the pull is then stronger even though I start increasing the throttle with similar slow speed as on D.
Does that sound good or I'm just paranoid? :stupid:
 
Last edited:

RAF_S7

Well-Known Member
Gold Supporter
What drive mode are you in when having the issues?

You said you have the box in manual mode, that means it will hang onto gears for much longer and it’s expecting you to change the gear (up or down), or it will change automatically when it revs too high, to protect the box.

Im a little confused with your technique of accelerating to 50 then taking your foot off the gas. What is it your trying to check by doing this?
If you lift off at 50 it will decelerate, and depending if the box is in D or S mode, it changes the gearing change points.

How does the car drive and gearing behave when your in normal Auto mode?
 

Rs3Life

Registered User
What drive mode are you in when having the issues?

You said you have the box in manual mode, that means it will hang onto gears for much longer and it’s expecting you to change the gear (up or down), or it will change automatically when it revs too high, to protect the box.

Im a little confused with your technique of accelerating to 50 then taking your foot off the gas. What is it your trying to check by doing this?
If you lift off at 50 it will decelerate, and depending if the box is in D or S mode, it changes the gearing change points.

How does the car drive and gearing behave when your in normal Auto mode?
In all tests drive mode was Dynamic.

Just to be clear I didn't rev to the end obviously (max between 5-6k). I was driving in automatic as well but it was hard to feel the difference. In auto when you release gas pedal the car will shift to higher gear once the revs will go down so you will feel the gear change anyway what made me unable to feel the weird pull sensation when the fuel supply is engaged or increased.

I did speak with a guy that owns a rs6 and he thinks it could be coil or spark plugs issues as he does not have such problems.
 
Top