SQ5 Engine Knocks and Smokes During Acceleration

Having some experience with engine issues, I encountered a similar problem with my 2014 S4. The symptoms were nearly identical, jerking during acceleration, power loss, and the telltale signs of engine knock. Initial diagnosis revealed carbon deposits in the combustion chamber, causing detonation issues. The knock sensors were picking up irregular combustion patterns, especially under load. After running tests, the workshop confirmed significant carbon buildup was disrupting proper combustion. The fix involved: 1. Complete cleaning of combustion chambers 2. Replacement of spark plugs 3. ECU recalibration 4. Fuel system cleaning Total cost came to 425 Euro, and the problem was fully resolved. The engine now runs smoothly with no piston slap or knocking sounds. A few questions to better assist: What fuel octane rating are you currently using? How many kilometers on the engine? Have you noticed any changes in fuel consumption? When did these symptoms first appear? Using higher octane fuel and regular fuel system cleaning can help prevent these issues from recurring.

Latest service was at 132000 KM, about 2 months ago. Running 98 octane fuel since day one. Fuel consumption increased by about 15% in the last 2 weeks. Problems started gradually but got much worse over the last few days. The ignition timing seems off based on the diagnostic readings from my OBD scanner. Engine knock is most noticeable between 2000-3000 RPM. Good point about the carbon deposits, the service records show no carbon cleaning was ever performed despite the high mileage. Your suggested repair steps make sense, especially given how the detonation issues match my symptoms. Will book it in and request they check the combustion chamber deposits first.

Thanks for the additional details, those symptoms definitely parallel what I experienced with my S4. The gradually worsening performance and increased fuel consumption, combined with knock detection between 2000-3000 RPM, strongly suggests carbon buildup affecting pre-ignition timing. Even with premium 98 octane fuel, carbon deposits can accumulate over time and disrupt proper combustion chamber conditions. At 132000 KM without previous carbon cleaning, this matches the timeline when these issues typically surface. After my repair, I learned a few key points: 1. The carbon cleaning restored proper ignition timing 2. Pre-ignition issues disappeared once deposits were removed 3. Fuel economy returned to normal within 2 tanks Would suggest requesting the workshop to: Check knock sensor values, Measure actual vs desired ignition timing, Inspect combustion chamber deposits, Test fuel pressure regulation This systematic approach helped identify the root cause in my case. The detonation issues completely resolved after cleaning. Consider scheduling that carbon cleaning service soon before the symptoms worsen further.

Thanks for sharing your experience. Your repair path seems to match exactly what I need. The connection between carbon deposits and pre-ignition makes perfect sense given my symptoms. Just booked the car in for next week. Made sure to mention all the knock sensor readings and ignition timing data from my OBD scanner. The workshop confirmed they will do a full combustion chamber inspection first, followed by carbon cleaning if needed. Really helpful to know your fuel economy normalized after fixing the detonation issues. Looking at around 450 Euro for the full service based on their quote, which seems reasonable considering the work involved. Will watch the fuel octane and carbon buildup more carefully going forward to prevent this from happening again. Hopefully this solves the rough running and power loss issues. Thanks again for the detailed repair info, gave me confidence to address this before it got worse.