S6 TDI Power Loss Linked to Cylinder Pressure Fault

Having dealt with a similar issue on my 2021 S4 TDI, I can share some relevant experience. With some experience working on diesel engines, this sounds familiar. The engine knocking and increased fuel consumption you describe matches what I encountered. In my case, the root cause was actually traced back to a previous repair where the fuel injectors were replaced incorrectly. This created uneven cylinder pressure and damaged several components in the process. The dealer covered all repairs under warranty since it was their mistake during the previous service. The fix involved: Complete diagnostics of the intake manifold and fuel delivery system, Adjustment of the camshaft timing, Replacement of damaged piston rings, Recalibration of all fuel injectors The repair took about 4 days to complete. Since this was warranty work, my total cost was 0 Euro. To provide more specific advice for your situation, could you share: Current mileage on your S6, When was the last major service performed, Any recent repairs or maintenance work, Are you getting any specific error codes, Does the engine knocking change with engine temperature Let me know these details and I can suggest more targeted solutions based on my experience.

Thanks for the helpful input on fuel injector and repair experience. Just updating that mine has 182547 KM and had its last full service including timing belt replacement 3 months ago. The engine knocking seems constant regardless of temperature. Got it scanned yesterday and error code points to cylinder 3 pressure issues, with possible crankshaft position sensor malfunction. Local mechanic quoted 2800 Euro just for diagnostic teardown, which seems excessive even for an S6. Any insights on whether this could be something simpler before going for major engine work?

Thanks for those additional details. Having gone through similar issues with my S4 TDI, I can relate to your concerns about the repair costs. The error code combination of cylinder pressure and crankshaft position sensor is interesting. Before doing a complete teardown, I would strongly suggest checking a few simpler potential causes that also affected my car: 1. The crankshaft position sensor itself might be faulty, this can cause false cylinder pressure readings and only costs around 300 Euro to replace 2. Have the fuel injectors tested individually. My situation started with one bad injector causing uneven cylinder pressure 3. Check the timing belt tension, even though recently replaced, incorrect tension can cause similar symptoms The engine knocking being constant regardless of temperature is similar to what I experienced before the injector issue was found. The 2800 Euro diagnostic teardown quote does seem high, my complete injector replacement and diagnosis cost 1200 Euro at an independent shop. Would recommend getting a second opinion specifically focused on the fuel injector and crankshaft sensor before authorizing major engine work. The timing belt being recently replaced could also be relevant if not properly tensioned during installation.

Thanks for this detailed perspective on the injector issues. After reading about your similar experience, I decided to get a second opinion. Found another shop willing to do targeted diagnostics of the crankshaft position sensor and injectors first for 400 Euro, which sounds much more reasonable. They also mentioned checking the head gasket since there might be compression leaks affecting cylinder pressure. Will have them start with inspecting the timing belt installation and testing the injectors before considering any major teardown work. The fact that your issue was resolved without needing extensive engine work gives me hope this might be simpler than initially feared. My warranty expired last month unfortunately, but 1200 Euro for injector work would be far better than the first quote I got. Will update once I know more after the initial diagnostic work next week. The spark plug and intake manifold will also get checked during this process, which seems like a sensible approach before jumping into major repairs. Really appreciate the detailed breakdown of your repair experience, helped me ask better questions at the second shop.