SQ7 Engine Power Loss & Knocking Points to Detonation

I had a very similar issue with my 2019 SQ8 4.0 TFSI. As someone with some hands-on experience maintaining performance engines, these symptoms immediately caught my attention. The main culprit turned out to be carbon deposits in the combustion chamber, which was affecting the proper fuel-air mixture and causing irregular combustion. The knock sensor was constantly adjusting timing to compensate for these detonation issues, leading to power loss and the jerking sensation you described. The repair involved: Complete diagnostic scanning, Cylinder heads inspection, Professional cleaning of combustion chambers, Replacement of spark plugs, ECU adaptation reset Total cost was 425 Euro and resolved all symptoms. The piston slap noise I initially feared turned out to be unrelated. Few questions to provide better guidance: What fuel octane rating are you using? How many miles/kilometers on the engine? Have you noticed any changes in fuel consumption? When was your last spark plug replacement? Any recent changes in driving patterns or fuel source? This information would help determine if your issue matches what I experienced or points to something different.

Thanks for sharing your experience. My current mileage is 93340 KM and last service was done at 85000 KM. I exclusively use high octane fuel (98) but recently noticed increased fuel consumption. The engine knock seems more pronounced during cold starts, which made me concerned about pre-ignition issues. No spark plug replacement has been done yet since the car is relatively new. I mainly do highway driving with occasional spirited acceleration, no track use. Started using a different fuel station about 2 months ago, roughly when these issues began appearing. These details align closely with what you experienced. Think I will have the combustion chamber inspected based on your feedback.

Thanks for those details. Your symptoms are incredibly similar to what I faced with my SQ8, and the timing with the fuel station change is particularly telling. The increased fuel consumption combined with cold start engine knock definitely matches the carbon deposit pattern I experienced. The knock sensor in these 4.0 TFSI engines is quite sensitive, and when carbon buildup reaches a certain point, it starts triggering detonation warnings more frequently. One thing I forgot to mention in my previous post, before the full service, I tried running a fuel system cleaner for two tanks, but it only provided minimal improvement. The carbon deposits in these direct injection engines often need professional cleaning, especially around the cylinder heads. Quick maintenance tip that helped prevent recurrence after my repair: Returned to my previous fuel station, Regular high rev driving (3000+ RPM) for brief periods, Strict adherence to 98 octane fuel Would recommend getting it checked soon, as continued detonation issues can potentially cause long-term damage. The repair cost I mentioned earlier might vary slightly, but catching it early prevented more extensive repairs in my case. Let us know what the inspection reveals. Always interested in tracking these cases since our engines are practically identical.

I really appreciate all this detailed feedback. The connection between the fuel station change and the onset of problems seems too significant to ignore. Your experience matches my situation almost perfectly, especially regarding the knock sensor behavior and cold start symptoms. The suggestion about fuel system cleaner being insufficient makes sense, given the direct injection setup. I will skip trying that step and go straight for the professional cleaning you described. The pre-ignition issues during cold starts have gotten more frequent lately, so addressing this sooner rather than later seems wise. My ignition timing adjustments are likely following the same pattern you experienced, with the ECU constantly compensating for the carbon buildup. Going to schedule the inspection next week and will request they specifically check the combustion chambers and cylinder heads. Will make sure to switch back to my previous fuel station immediately. The correlation with the fuel source change and these problems is too strong to dismiss. Your maintenance tips about high rev driving and strict fuel octane requirements will be helpful for preventing future issues. Thanks again for helping me avoid potentially more expensive repairs down the line. Will update the forum once I get the inspection results and complete the service.