Bad Misfiring

[Vieussuex*]

Hey guys, just wondering if anyone has suffered a misfire so bad the ECU decides to shut down the problem cylinder?
If so have what were the causes. For example a bad spark plug, failing coilpack, blocked or failing injector or the dreaded carbon build up?

Car has been getting occasional misfires on start up but disappears when warmed up, but the last 2 days has been constant regardless of warming up.
I've had the car for approx 12 months and never had an issue. Car is about 6 years old and looks like still running on the original coilpacks and never had a carbon clean either, so it probably requires one.
I should probably also ask has anyone had a carbon clean and did you get the stealership or an indy to do it and what did they charge?

Vagcom logs below
3 Faults Found:

000768 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - Intermittent
Freeze Frame:
Fault Status: 00100001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 96972 km
Time Indication: 0
Date: 2016.10.15
Time: 15:55:13

Freeze Frame:
RPM: 2303 /min
Load: 15.7 %
Speed: 37.0 km/h
Temperature: 81.0°C
Temperature: 57.0°C
Absolute Pres.: 1010.0 mbar
Voltage: 13.081 V

000776 - Cylinder 8
P0308 - 001 - Misfire Detected - Intermittent
Freeze Frame:
Fault Status: 00100001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 96972 km
Time Indication: 0
Date: 2016.10.15
Time: 15:55:13

Freeze Frame:
RPM: 2303 /min
Load: 15.7 %
Speed: 37.0 km/h
Temperature: 81.0°C
Temperature: 57.0°C
Absolute Pres.: 1010.0 mbar
Voltage: 13.081 V

004874 - Cylinder Disabling
P130A - 001 - - Intermittent
Freeze Frame:
Fault Status: 00100001
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 96974 km
Time Indication: 0
Date: 2016.10.15
Time: 16:33:05

Freeze Frame:
RPM: 2442 /min
Load: 38.0 %
Speed: 19.0 km/h
Temperature: 93.0°C
Temperature: 72.0°C
Absolute Pres.: 1010.0 mbar
Voltage: 12.700 V

[Ian_C]

Have you changed the spark plugs in your ownership? Or is there a cast iron receipt in the history file saying they have been done before you bought it 12 months ago? This would be the first thing I'd change. The car has done 60,000 miles so they are due around now anyway? A dodgy tank of fuel can cause cars to run rough, but would not cause the same cylinder to misfire every time, so unlikely to be that. If spark plugs don't solve, then try testing one new coil pack on the cylinder at fault. You definitely want to cross these off the list first before taking the engine for a carbon clean!

[discostu49]

I'm not so savy with codes and all that jazz but my old car would miss fire on cold days turned out to be the battery needing changed ....

[Vieussuex*]

Have you changed the spark plugs in your ownership? Or is there a cast iron receipt in the history file saying they have been done before you bought it 12 months ago? This would be the first thing I'd change. The car has done 60,000 miles so they are due around now anyway? A dodgy tank of fuel can cause cars to run rough, but would not cause the same cylinder to misfire every time, so unlikely to be that. If spark plugs don't solve, then try testing one new coil pack on the cylinder at fault. You definitely want to cross these off the list first before taking the engine for a carbon clean!

I'm not so savy with codes and all that jazz but my old car would miss fire on cold days turned out to be the battery needing changed ....

I can't be sure the spark plugs have been replaced, my last fluid change I asked if we could change the plugs and my mechanic (who is an Audi indy specialist) said to wait for my major service which is due in about 5,000km. I've always used the same service station for fuel - BP Ultimate 98ron. When I first got the car I replaced the battery with a top of the range Narva with increased CCA.

Come to think of it this all started when I went for a spirited drive with a e97 M3 probably pushed up to about 4th gear, I let it cool down after before shutting her off and then a few hours later on cold start it had a terrible misfire when I fired her back up.....maybe I killed a coilpack?

I just hope it's sparkplugs or a coil pack. My brother got a carbon clean on his 2.0T and that was AUD $1,500 of labour.... I couldn't imagine it being cheap getting a carbon clean on a 10cyl engine.

[TomRS]

You wont need a carbon clean on the RS6...

I have had the inlet off my old one (when replacing a fuel pressure sensor) that had nearly 90k on and there was tiny tiny amounts of carbon buildup, the Carbon problems mainly affect the 5.2L V10 in the S6 and the 4.2 V8 in the RS4 B7, carbon buildup shouldnt be a problem on a turbocharged car as the air if forced in thus blowing the carbon away. (simple way of explaining it)

As for your missfire i'd be very careful using the car, i had an injector go bad and it actually washed the bore, these things fuel very heavily... although if it is shutting down the cylinder then it'll be stopping fuel supply so it wont cause further damage.

Start with plugs, just hope you havent dropped a tip and smashed a valve as that would be bad news, a compression test and inspection with a borescope would confirm or deny this (obviously if the plug isnt missing its tip then i wouldnt worry)
Get a coil pack at the same time and replace both, hopefully this solves your issue.. if its not that then it'll be down to an injector (but as i said a compression and leak back test will confirm or deny any issues with the cylinder itself.

[Vieussuex*]

Good News it was just a bad spark plug so had all 10 replaced just incase. Thanks for input and advice people!

[Ian_C]

Good News it was just a bad spark plug so had all 10 replaced just incase. Thanks for input and advice people!