Audi S8: Torque Issue? Check ECU Data Now!

Hello,

I used VAG-COM to read the measurement blocks from the engine and transmission control units of my Audi S8 (4.2L V8, 360 hp) to determine the maximum torque. For the engine control unit, I looked at blocks 120/122, and for the transmission control unit (5-speed Tiptronic), I examined measurement block 009. However, instead of the expected 430 Nm, I'm only reaching a maximum of 308 Nm. I've done several test drives (full-throttle acceleration, highway driving with multiple rapid accelerations), but 308 Nm is the highest torque I've ever measured. There are no error codes stored in the error memory.
I don't feel like the car is running poorly, but with a gradual loss of power, you might not notice it as easily.
The main reason I wanted to determine the torque was due to a transmission issue. Earlier this year, I had a transmission failure. The workshop said that the transmission failed because the engine control unit was sending incorrect, too-low torque values. In reality, the torque values were always higher, which caused the transmission to wear out very quickly. Apparently, this is a known problem with Audi vehicles and can only be detected through dyno tests, not by reading the error memory. The engine control unit was replaced along with the transmission.

I'm now wondering the following:
- Is it reporting a low torque again? That would explain why I don't feel like the car is running poorly. Also, it would put a lot of stress on the transmission again.
- Are the values actually correct, and is the car truly not delivering its full power? If so, the question is what's going on and why there's no error code in the memory. I need to measure this again with a higher sampling rate, but during a sprint from 0 to 100 km/h, based on the speed readings and timestamps when logging the measurement groups, I saw that it takes about 7.8 seconds to reach 100 km/h. Normally, the sprint should be completed in just over 6 seconds. This might be an indication of a lack of power.

Can someone give me some hints or tips on what might be going on, or what things I should check to figure out what's wrong?

Thank you in advance.

Best regards,
hotel-lima

However, the incorrect temperature readings in your example were transmitted due to a coolant temperature sensor that was not functioning correctly. They should have been able to tell you that completely from the start.


Since that part doesn't cost a fortune, it might be worth considering replacing it.

Hello,

"This should then be determinable with the help of the measurement groups, right? I saw in a description of the measurement groups from Ross-Tech that there are several measurement groups that provide various temperatures. Which one would be relevant here?"

Best regards,
hotel-lima

Hi,

How about the coolant temperature reading in the engine control unit?

Best regards, Rainer.

Hello,

I was a bit puzzled by the measurement groups 130-137, as it appears that temperatures are being measured at different points there.

Best regards,
hotel-lima

Hello.

"It would be a good idea to check the mass airflow sensor (MAF). It's a known issue, even in the S8. I've experienced it several times. After checking it, the values were around 310 Nm, and the airflow was approximately 115 grams."

The statement from Audi about the torque , I'm not quite sure about...




Best regards, Cosi.

Hello,

It didn't make sense to me either. But what can a customer do without accurate information and insider knowledge?
That's also the reason why I'm looking into this now. I don't want to rely entirely on the diagnoses from the workshop...
I'll take a look at the LMM (mass airflow sensor) and the coolant temperature sensor tomorrow.
What are the specified values for the mass airflow rate (MAF) for the S8? My last information was a minimum of 280 g/s at 7000 RPM. Is that correct?

Best regards,
hotel-lima

Hello.

I don't have the exact values memorized right now, but I think it's around 160g/s. I'll need to check on my computer tomorrow.
Coolant temperature can either be checked by measuring the resistance at a specific temperature, or by relying on the readings obtained using VCDS (VAG Com diagnostic software).

Regarding torque, it's just a calculated value and can be affected by various factors, such as injection time and load.
Do you perhaps have a chip inside?


Best regards, Cosi.

Hello,

No, there's no chip installed. Everything is 100% in its original condition.

So, could it be that the displayed torque is lower than the actual torque being applied, and thus the transmission is being damaged as a result?

Best regards,
hotel-lima

Hello,

I just completed a test run. The coolant temperature sensor is providing valid readings, and I observed a temperature increase from approximately 50°C to 90°C.

I also logged the mass airflow sensor data once. The maximum value was 199.69 g/s at 6920 RPM and 100% load.

Code:

Time      U/min        LMM g/s    load%      Ign. 0BTDC    31.79   680   7.94   3.1   0.0    32.09   680   7.56   3.1   0.0    32.39   680   7.64   3.1   2.3    32.69   760   11.89   5.1   22.5    33.00   920   19.08   7.8   21.0    33.30   1440   28.50   11.8   23.3    33.60   1760   50.31   27.8   23.3    33.91   2160   56.11   59.6   24.0    34.21   2600   78.97   100.0   22.5    34.51   3040   98.75   100.0   21.0    34.82   3560   115.11   100.0   21.8    35.12   4080   136.31   100.0   23.3    35.44   4640   143.78   100.0   27.0    35.78   5200   163.25   100.0   27.8    36.14   5760   168.94   100.0   29.3    36.51   6360   184.08   100.0   30.8    36.89   6840   192.64   100.0   21.8    37.27   6880   192.39   100.0   6.8    37.63   5800   169.72   100.0   3.8    37.97   5000   143.14   100.0   30.8    38.31   5240   159.83   100.0   30.0    38.65   5440   157.64   100.0   30.0    39.01   5680   166.61   100.0   30.0    39.37   5880   181.86   100.0   30.8    39.74   6080   178.86   100.0   30.8    40.11   6320   186.89   100.0   31.5    40.49   6520   189.19   100.0   31.5    40.87   6720   191.78   99.6   32.3    41.24   6840   189.19   100.0   21.0    41.62   6440   193.53   100.0   6.0    41.96   5160   153.53   100.0   6.0    42.30   5000   152.83   100.0   30.8    42.63   5040   154.94   100.0   30.0    42.97   5120   151.14   100.0   30.0    43.31   5160   146.50   100.0   30.0    43.65   5240   154.94   100.0   30.0    43.99   5320   155.22   100.0   30.0    44.34   5440   151.42   100.0   30.0    44.69   5480   162.81   100.0   30.0    45.04   5560   161.58   100.0   30.0    45.39   5640   172.89   100.0   30.0    45.75   5760   179.39   100.0   30.0    46.11   5840   173.97   100.0   30.8    46.47   5880   148.39   48.6   15.0    46.82   5840   42.47   12.9   19.5

Code:

Time      U/min        LMM g/s    load%      Ign. 0BTDC 61.21   4680   169.61   42.4   27.8 61.53   4800   146.67   100.0   27.8 61.86   4880   144.83   100.0   29.3 62.20   4960   150.83   100.0   30.8 62.53   5080   151.61   100.0   30.0 62.87   5200   159.61   100.0   30.0 63.22   5320   157.39   100.0   30.0 63.56   5480   154.03   100.0   30.0 63.92   5600   167.72   100.0   30.0 64.27   5760   176.08   100.0   29.3 64.64   5880   172.11   100.0   30.8 65.00   6000   175.61   100.0   31.5 65.37   6160   176.39   100.0   31.5 65.75   6280   177.22   100.0   28.5 66.12   6440   181.31   100.0   28.5 66.50   6560   190.92   100.0   31.5 66.88   6680   194.42   100.0   32.3 67.25   6800   187.56   100.0   25.5 67.63   6920   199.69   100.0   20.3 68.01   6480   186.36   100.0   5.3 68.35   4960   144.31   100.0   8.3 68.68   4800   136.39   100.0   29.3 69.00   4800   136.33   53.3   13.5 69.32   4760   30.92   10.2   15.0 69.65   4720   15.69   6.3   23.3 69.97   4640   16.53   6.3   30.8

According to the information I have, the target values are between 280 and 300 g/s. Can anyone confirm this? If that's correct, then my mass airflow sensor (MAF) is apparently providing too low values. I would then check the MAF sensor and try to determine if the catalytic converters are functioning properly.

Best regards,
hotel-lima