I have a 2011 mk6 golf TSI. I bought it as a project, it had eng, epc light and it was running rough. Here is the diagnosing processes I followed as this seems to be a very common fault.
1. Checked obd codes, found p303 misfire cyclinder 3.
2. Replaced spark plugs, cyc3 was very oiled and black.
3. Replaced cyc3 coil.
4. Reset codes and test
5. Replaced cyc 3 fuel injector.
No progress still have error and misfiring.
Compression test on cyc3. Found to be 50psi, should be 140-160. Next step is to remove the head and clean and reseat the valves. Upon inspection the back of all valves were found to have a large build up of carbon. I'll post photos and videos soon.
Just pulled the sump... found lots of frag. Pulled piston 3, lots of damage to the skirt around the gudgun pin. Explains the cylinder misfire and lack of compression. New piston on the way from the UK, and a new set of valves locally.
So, pulled all the pistons, new rings and replaced #3 piston with new oem part. Light hone of all cyclinders. Removed supercharger inspected and serviced (easy to do while the he'd is off). All new valves, valve seats ground to match the new valves.
Re assembly carried out. New oil and filter. Radiator and coolent system flushed. New spark plugs.
Started almost straight away, once the fuel had primed. Once the oil flow stabilised it ran really nice. Have had a short test drive around town, it seems to be running great. Just need to run in the new rings and it will be back to normal.
All up costs;
-car - $6099
-parts - $1452 + on road costs
I have seen quotes as high as $8000 to do the same job!