S7 2016 cylinder 8 misfires

[John336]

Suddenly getting multiple misfires per second on cylinder 8, CTGE engine.
Stock S7 2016 w/ 91k miles. Spark plugs have been changed 17400 miles / 3½ years ago.
The PCV failed 2½ years ago and was replaced. The oil screen issue was fixed 6½ years ago with new turbos. Both HPFPs were replaced 4½ years ago.

The only DTCs are the following:

3 Faults Found:

10203 - Random/Multiple Cylinder Misfire Detected 
          P0300 00 [11101101] - -
          MIL ON - Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Priority: 2
                    Fault Frequency: 1
                    Mileage: 147800 km
                    Date: 2025.03.09
                    Time: 03:00:38

                    Engine speed: 1563.00 /min
                    Normed load value: 14.1 %
                    Vehicle speed: 22 km/h
                    Coolant temperature: 72 °C
                    Intake air temperature: 20 °C
                    Ambient air pressure: 990 mbar
                    Voltage terminal 30: 14.229 V
                    Unlearning counter according OBD: 40
                    Engine status: COENG_RUNNING
                    Engine status-Test_Program_Co Eng st COMPU VERB UBYTE: 3

10598 - Cylinder 8 
          P0308 00 [11101101] - Misfire Detected
          MIL ON - Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Priority: 2
                    Fault Frequency: 1
                    Mileage: 147800 km
                    Date: 2025.03.09
                    Time: 03:00:38

                    Engine speed: 1563.00 /min
                    Normed load value: 14.1 %
                    Vehicle speed: 22 km/h
                    Coolant temperature: 72 °C
                    Intake air temperature: 20 °C
                    Ambient air pressure: 990 mbar
                    Voltage terminal 30: 14.229 V
                    Unlearning counter according OBD: 40
                    Fuel pump: specified value: 30.035 %
                    Fuel low pressure: actual value: 495.0 kPa
                    Low fuel pressure: specified value: 494.6 kPa
                    Oxygen sensor 1 bank 1: lambda actual value: 0.9905
                    Oxygen sensor 1 bank 2: lambda actual value: 1.0146
                    Selector lever position-Bits 0-7: 5

10205 - Cylinder Disabling 
          P130A 00 [00100100] - -
          Intermittent - Not Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Priority: 2
                    Fault Frequency: 3
                    Mileage: 147800 km
                    Date: 2025.03.09
                    Time: 03:00:53

                    Engine speed: 681.50 /min
                    Normed load value: 7.5 %
                    Vehicle speed: 0 km/h
                    Coolant temperature: 48 °C
                    Intake air temperature: 37 °C
                    Ambient air pressure: 990 mbar
                    Voltage terminal 30: 14.229 V
                    Unlearning counter according OBD: 40
                    Engine status: COENG_RUNNING
                    Engine status-Test_Program_Co Eng st COMPU VERB UBYTE: 3

Readiness: 0000 0000

"
Here you can view the 01 - Engine Advanced Measurement Values (blockmap) as scanned by VCDS while the engine is idling. Notice e.g. IDE03879 "Misfires per 1000 revolutions of cylinder 8" is 181:
https://docs.google.com/spreadsheets...gid=2012891888

The factory tool ODIS is telling me to:
1) Check the cyl8 ignition coil harness connector for water penetration and contact corrosion & bent and pushed-in pins.
2) Check the correct installation of the relevant ignition coil.
3) Check the spark plug shaft for accumulation of moisture such as oil, grease or water.
4) Check the spark plug insulator for burning marks.
5) Check the spark plug visually
6) Swap the spark plug & ignition coil with various cylinders, perform a road test and check whether the malfunction migrated.

Any other advice ?

Is this likely just a spark plug failure ?

[BasicBlack]

I'm always a big fan of a compression test before throwing parts at a problem like this. That'll provide a more definitive diagnosis. From there, you could boroscope the Cylinder for a closer look. (carbon build up or piston / valve /cylinder issues) Naturally, you'd hope it was as simple as a coil or plug. Start with the worst case and work your way back to the simple for piece of mind.

All the best!

[Akakios]

I'm always a big fan of a compression test before throwing parts at a problem like this. That'll provide a more definitive diagnosis. From there, you could boroscope the Cylinder for a closer look. (carbon build up or piston / valve /cylinder issues) Naturally, you'd hope it was as simple as a coil or plug. Start with the worst case and work your way back to the simple for piece of mind.

All the best!

This is good advice if it suddenly started to act out and you weren't working on it prior to induce the issue.

If you've removed anything on the motor and put it back, it's entirely possible to have a vacuum leak but that usually shows up as a random misfire and impacts a whole bank versus just a single cylinder.

[John336]

My local car mechanic says it's likely the coil that has gone bad.

[John336]

So it was a bad coil after all (Eldor 079 905 110 N, made in Turkey in July 2019). Probably killed gradually by heat.
The plug was fine, albeit a little wet (was cleaned with a torch).

Maybe those Hitachi coils are more robust (both Hitachi & Eldor are listed as OEM for the car) ?
Eldor coils are 079 905 110 J -> N -> R (supersession).
Hitachi coils are 079 905 110 K -> L -> P (supersession).