RS5 Power Loss & Stalling: Fuel Injection Alert

Had a similar issue with my 2017 RS4 last summer. Have some experience working on cars but mainly basic maintenance stuff. The symptoms you describe match exactly what I encountered, poor engine performance, high fuel consumption, and occasional stalling. Initially thought it was just dirty injectors, but the smoke during acceleration was the key indicator of a bigger problem. After proper diagnosis, turned out there was a faulty wiring connection to the fuel injection system. The damaged cables were causing irregular fuel delivery and air-fuel mixture problems. Had it fixed at a workshop, they replaced the damaged wiring harness and checked all connector plugs. Total repair cost was 95 Euro and it completely resolved the issues. To provide more specific advice about your case, could you share: Current mileage on your RS5? When did you first notice the symptoms? Have you had any recent maintenance work done? Does the check engine light come on? Is the smoke white, black, or blue? These details would help determine if your issue is similar to what I experienced with the wiring. Regular maintenance of the fuel system can prevent these problems, but sometimes connector issues develop regardless.

My maintenance history shows the last service was done at 13000 KM, just about 900 KM ago. The smoke is definitely black during acceleration, and yes, the check engine light started flashing intermittently last week. The engine performance issues began shortly after that. The system diagnostics from my regular workshop showed slightly irregular fuel pressure readings, which seems to align with your wiring harness theory. The engine response has been quite unpredictable, especially during cold starts. Would you recommend checking the wiring connections first before replacing any fuel injection components? The diesel vs gasoline difference might affect the diagnosis, but the symptoms sound very similar to your experience.

Thanks for the additional details. Those symptoms indeed match my wiring harness problem even more closely now. The black smoke combined with irregular fuel pressure readings strongly suggests a fuel delivery issue, which in my RS4 was directly related to faulty wiring connections affecting the fuel system. Before jumping to expensive injection component replacements, checking the wiring is definitely the smart first step. In my case, the intermittent check engine light was also a telltale sign of electrical issues rather than mechanical fuel system problems. The unpredictable engine response during cold starts particularly resonates with my experience. This happens when the engine management system cant properly regulate the air-fuel mixture due to inconsistent electrical signals. A quick diagnostic approach that worked for me: Have the workshop check all wiring connectors to the injection system, Test the fuel pressure sensor connections, Verify the integrity of the main engine harness near the fuel rail, Run a complete system diagnostic with focus on electrical values The maintenance interval you mentioned is quite recent, so its unlikely to be a regular wear issue. Based on my repair experience, Id strongly lean toward checking the electrical connections before replacing mechanical components. Would you mind updating us after the wiring inspection? It could help narrow down if your case matches mine.

Thanks for all the detailed feedback. Just had the workshop check the wiring harness connections as suggested, and you were spot on. They found corroded pins in two main fuel system connectors and some damaged insulation on the wiring near the fuel rail. The petrol injection system was actually working fine, it was just getting irregular electrical signals due to the bad connections. Total repair cost came to 120 Euro for replacing the damaged section of the harness and cleaning all connector pins. After the fix, the engine performance is back to normal, no more black smoke or power loss issues. Fuel consumption has also returned to standard levels. The mechanic mentioned this type of electrical issue is somewhat common in these engines due to the connector placement. Really appreciate the advice about checking the wiring before jumping into expensive injection system repairs. Saved me a lot of money and got my car running properly again. Will definitely keep an eye on these connections during future maintenance checks.