Audi S6 Power Loss and Rich Fuel Mix Needs Diagnosis

Having experienced similar symptoms with my Audi S4 (2013), this sounds like a faulty fuel injector. When my car showed these exact issues, power loss, increased fuel consumption, and jerky acceleration, the root cause was a defective injection valve that was causing improper fuel atomization. The check engine light activation combined with rough running often indicates an air-fuel ratio imbalance. In my case, the faulty injector was dumping too much fuel into the cylinder, creating a rich mixture condition. The oxygen sensor readings confirmed this diagnosis. The repair required removing the intake manifold to access and replace the problematic injector. It was a serious issue that needed immediate attention, as continuing to drive with a malfunctioning injector risks damaging the catalytic converter due to unburned fuel. Testing revealed that one injector was stuck partially open, while the others were functioning normally. The repair involved replacing the faulty injector and cleaning the remaining ones to ensure proper spray patterns. The job took about 4-5 hours of labor. A proper diagnosis should include: Computer diagnostic scan, Fuel pressure testing, Individual injector performance testing, Checking oxygen sensor readings

Thanks for sharing your S4 experience. Your situation sounds identical to what I went through with my injector problems. After reading your detailed explanation, I am even more convinced we had the same issue. The rich mixture symptoms and power delivery problems match exactly. I would be curious to know what the total repair cost was in your case? Also, have you experienced any related problems since the injector replacement? My fuel economy has been great after the fix, but I like to hear long-term feedback from others who went through similar repairs. The air-fuel ratio issues seemed to resolve completely after the repair in my case, but I am wondering if you needed to replace the oxygen sensor as well, since you mentioned those readings in your diagnosis process.

After getting the faulty injector replaced last month, the engine has been running perfectly. The repair bill came to 515 Euro total, which included parts and labor. The rich fuel mixture issue was completely resolved, fuel economy returned to normal and the power delivery is now smooth again. The oxygen sensors were actually fine and didnt need replacement. They were just reporting the rich condition accurately due to the stuck injector flooding that cylinder with excess fuel. After the new injector was installed, the air-fuel ratio returned to optimal levels on its own. The catalytic converter also escaped damage since I addressed the problem quickly. Regular maintenance checks of the fuel system components can help catch these issues before they cause wider problems. My air filter was also cleaned during the service, which helped ensure the engine was getting proper air flow for ideal combustion. The spark plugs were inspected too, but showed no carbon buildup from the rich running condition. Overall, catching and fixing the bad injector early prevented more expensive repairs down the road.

After reading about your experience, I finally took my S6 to a mechanic last week. The diagnosis confirmed what you suggested, a faulty fuel injector. The repair cost came to 490 Euro, slightly less than yours, and took about 4 hours to complete. The mechanic found that cylinder 3 had a stuck injector, causing the rich mixture. They replaced it and cleaned the others while the intake manifold was off. The oxygen sensor readings went back to normal after the fix, confirming the problem was solved. My fuel economy has improved dramatically, back to what it should be. The jerky acceleration is completely gone, and the engine runs smooth as silk now. The check engine light hasnt come back on either. The mechanic also checked my air filter and spark plugs during the service. Everything else looked good, so no additional repairs were needed. Really glad I got this sorted before it could damage the catalytic converter.