A4 TDI Running Rich: Power Loss & Engine Troubles

Had a similar issue with my 2017 A4 2.0 TDI. Been working on cars as a hobby for several years, so I have some experience with diesel engine problems. The symptoms match exactly what I experienced, poor fuel economy, stuttering during acceleration, and constant check engine light. In my case, it turned out to be a faulty injection valve. The air-fuel ratio was completely off, causing excessive fuel consumption and power loss. Initially thought it might be related to a clogged air filter or oxygen sensor, but diagnostic tests confirmed it was an injector problem. Had it fixed at a workshop, total repair cost was 515 Euro including parts and labor. The difference in performance after replacement was night and day. Before suggesting specific solutions, could you share: Current mileage on your A4? Any recent maintenance work done? Does the problem get worse when the engine is cold or warm? Any unusual sounds or smoke from the exhaust? This information would help narrow down if your issue is similar to what I experienced with the injector or if it might be something else.

Thanks for the detailed response. My A4 has 9008 KM and had its last service 3 months ago. The symptoms definitely worsen when the engine is warm, and there is black smoke from the exhaust during acceleration. Looking at your experience, the symptoms do match. The air-fuel ratio issues and black smoke strongly suggest a fuel system problem. The catalytic converter seems to be functioning normally based on earlier tests, so your injector theory makes sense. Will get the fuel injectors checked. Thanks for sharing the repair costs, helps with budgeting for the fix.

Thanks for the follow-up. Given your relatively low mileage of 9008 KM, my suspicion about the fuel injectors is even stronger now, especially with the black smoke during acceleration. On my A4, the black smoke was also a telltale sign of faulty injectors causing excess fuel delivery. The fact that symptoms worsen with a warm engine matches my experience exactly. When the engine heats up, faulty injectors often stick open longer than they should, leading to that rich fuel mixture. The check engine light in my case was specifically related to the fuel trim being out of normal range. Since your car is still fairly new, its worth checking if this might be covered under warranty. My repair cost of 515 Euro was out of pocket since my car was older, but your 2019 model might still have coverage. One thing I noticed after fixing the injectors was an immediate improvement in fuel economy and the catalytic converter stayed cleaner since it wasnt dealing with excess fuel. The entire acceleration response became much smoother too. Just make sure the workshop performs a proper fuel injector diagnostic test rather than just a basic check engine light scan, as this will confirm if were dealing with the same root cause.

The black smoke and rich mixture symptoms definitely point toward the injection system. The detail about warranty coverage is particularly helpful since my A4 should still be under the original warranty period. I called the dealership and theyve agreed to perform a complete fuel system diagnostic under warranty. The service advisor mentioned they will specifically test the injectors and fuel pressure regulation, given the symptoms match common fuel delivery issues. The connection between warm engine performance issues and stuck injectors makes perfect sense. Its reassuring to know the fix made such a clear difference in your case, especially with fuel economy and acceleration response. Will update once the diagnostic is complete, but feeling more confident now about the likely cause. The black smoke during acceleration combined with the rich mixture readings seems to be a classic sign of injector problems, just as you experienced. Thanks for helping identify the probable culprit before taking it to the shop.