Audi A4 Diesel Injection System Causing Multiple Issues

Had the exact same symptoms on my 2008 Audi A3 diesel (similar fuel system). Based on my limited experience with diesel engines, these symptoms typically point toward electrical issues in the injection system. The black smoke, high fuel consumption, and power loss were identical to what you describe. After some diagnostics, the workshop found a faulty wiring connection to one of the fuel injectors. The system was not getting proper signals, causing incorrect fuel delivery timing. The fix involved replacing the damaged wiring connector and testing all injection system connections. Total cost was 95 Euro including diagnostics and repair. Before jumping to conclusions though, could you share: Any error codes showing up? When did these symptoms first appear? Has the car been exposed to water/moisture recently? Any recent fuel system maintenance? This would help narrow down if your issue matches what I experienced, as similar symptoms can have multiple causes in the fuel injection system.

My Audi has 151453 KM on the clock with the last service done 3 months ago. No error codes are showing, but the symptoms started appearing gradually over the last 2 weeks. The engine stalling has become more frequent in the past few days. No recent exposure to water or moisture, and no fuel system maintenance was done during the last service. The black smoke is particularly noticeable during cold starts, and the diesel consumption has increased by about 3L/100km compared to normal. I checked the fuel filter and it seems clean, but I understand there could be other components in the injection system causing these issues. Would you recommend getting the wiring connections checked first, or should I go for a complete diagnostic of the fuel system?

Thanks for the additional details. Your symptoms actually sound a bit different from what I experienced, even though they initially seemed similar. The gradual onset and lack of error codes points more toward a mechanical issue in the fuel system rather than the electrical problem I had. In my case, the symptoms appeared suddenly and the engine management light came on immediately. The fact that your issues are worse during cold starts and developed gradually suggests possible injector wear or fuel pump problems affecting system performance and fuel pressure. Based on the mileage and symptoms, I recommend getting a complete fuel system diagnostic rather than just checking wiring. My initial electrical fix was simpler, but your case sounds more like worn injectors or a failing fuel pump, both common issues at this mileage that affect power delivery and fuel consumption. The diagnostic should include: Fuel pressure testing, Injector spray pattern analysis, Fuel pump performance check, Complete system scan for stored codes The full diagnostic costs around 150 Euro but will identify the root cause. If it is injectors, expect repair costs between 800-1200 Euro depending on how many need replacement. Still cheaper than continuing with poor performance and excessive fuel consumption.

The symptoms you describe do point toward different fuel system issues than what I initially suspected. Since my problems appeared suddenly with warning lights, while mine developed gradually without codes, I agree we are likely dealing with different root causes. I will definitely get the complete diagnostic done first rather than just checking the wiring connections. The excessive diesel consumption and black smoke during cold starts are concerning enough to warrant a thorough inspection of the injection system. Will book the car in next week for the full diagnostic including the fuel pressure testing and injector analysis you suggested. 150 Euro for peace of mind seems reasonable, even if repair costs end up being higher. Better to fix it properly now before the symptoms get worse or cause additional damage. Thanks for the detailed comparison with your experience. Really helped me understand why my gradual power loss and cold start issues likely need a different approach than your electrical fix. Will update once I get the diagnostic results.