SQ5 TDI Power Loss Points to Failing Piston Rings

Having dealt with similar symptoms on my Q5 3.0 TDI from 2014, I can share some relevant experience. As someone with moderate experience working on diesel engines, this turned out to be quite an interesting case. Initially, I also thought it was piston rings or a head gasket issue due to similar symptoms, increased fuel consumption, power loss, and engine warning light. However, after taking it to the workshop, they discovered the root cause was actually a timing belt that had skipped a tooth due to a faulty tensioner. This had caused slight misalignment of the crankshaft timing, leading to poor combustion and the symptoms you described. The repair was covered under warranty since it was a consequential issue from an improperly installed tensioner during routine maintenance. The total cost would have been around 1200 Euro, but I paid 0 Euro due to the warranty coverage. To better assist with your specific case, could you provide: Current mileage, Service history details, Any engine knocking or unusual sounds, Whether the engine has had previous major repairs, Recent maintenance work performed This information would help determine if your situation might be similar or if we are looking at a different underlying issue.

Last serviced 2 weeks ago at 198960 KM. After checking the service records, there was a fuel injector replacement done then. The timing belt was also inspected and appeared fine. The symptoms started right after that service actually. Had them look at the intake manifold too since there was some hesitation on acceleration. The camshaft position sensor readings were normal according to the diagnostic report. Your timing belt issue is interesting, will definitely have them check the tensioner during the next visit. The spark plugs are still original though, so maybe that needs attention too. Hoping its not as serious as piston rings.

Thanks for the additional details. Given the timing of your symptoms starting right after the fuel injector replacement, this could point to a different issue than what I experienced with my timing belt. With fuel injectors being replaced recently, there is a possibility of an improper installation or a faulty new injector. When I had my timing belt issue, the symptoms developed gradually, unlike your sudden onset after service. The spark plugs being original is concerning, on these engines they should typically be changed every 60000 KM. Poor spark can definitely contribute to combustion issues and increased fuel consumption. From similar experiences shared in the owners community, I would suggest having them check: The fuel injector installation and seating, Fuel pressure at the rail, Spark plug condition and gap settings, Compression test on all cylinders to rule out head gasket concerns My repair ended up being straightforward once properly diagnosed, and yours might be similarly manageable, possibly just needing the recent work double-checked rather than major engine work. Consider requesting a fuel injector leak-off test. This can quickly show if any of the new injectors are not performing correctly. My timing belt experience taught me that proper diagnosis is crucial before replacing major components.

The timing on these issues starting right after the service really points to something related to that fuel injector work. I will specifically ask them to verify the installation and run a leak-off test on the new injector. Makes sense to check the spark plugs too since they are original, definitely overdue for replacement based on the mileage. I have an appointment scheduled for next week. Will ask them to do a full compression test to rule out the piston rings and head gasket concerns. The timing belt tension check is also on my list now after hearing about that similar case. Better to be thorough and check everything while they are diagnosing it. Really hoping its just an issue with that recent injector work rather than something more serious. The fuel consumption increase is getting expensive. Will update once I get the results back from the workshop visit. Thanks for sharing those diagnostic suggestions, gives me a much better checklist to discuss with the technician.