S8 Fuel Pump Failure Symptoms & Repair Guide

As someone with some car repair experience, I dealt with similar fuel system issues on my 2011 S6 last year. The symptoms you describe match exactly what I experienced, engine stalling, rough idling, and increased fuel consumption. Initially, I also suspected a fuel pump failure. After taking it to the workshop, diagnostic testing revealed it was actually just a faulty wiring connection to the fuel injector system. The cable connection had deteriorated over time, causing inconsistent gasoline delivery to the engine. The repair was relatively straightforward, they replaced the damaged wiring and connections for 95 Euro, and the car has run perfectly since then. The entire repair took about 2 hours, much quicker and cheaper than replacing the entire fuel pump assembly would have been. If your symptoms are identical, you might be dealing with the same issue. Before making any definitive suggestions though, could you share: Current mileage? Any recent fuel system maintenance? Are you getting specific error codes? Does the problem occur more when the engine is cold or warm? This information would help determine if your issue matches what I experienced or if you might be dealing with something different.

Last service was completed at 29500 KM, where the technician performed a thorough automotive diagnosis but found no fuel system issues at that time. Started experiencing these problems about 200 KM after the service. The error codes point to P0171 and P0087, suggesting lean fuel mixture and low fuel rail pressure. The starting issues are more pronounced when the engine is cold, and the fuel injector problems seem worse during morning starts. Testing shows inconsistent gasoline delivery rates, which aligns with the previous reply suggesting potential wiring issues.

Thanks for providing those details. Looking at your error codes and symptoms, I need to revise my earlier assessment about it being just a wiring issue. On my S6, when I dug deeper after getting similar codes, the root cause turned out to be more complex than initially thought. The P0171 (lean mixture) combined with P0087 (low rail pressure) strongly suggests a fuel delivery problem that could stem from either the fuel pump or the fuel injectors themselves. Auto repair specialists eventually found that 2 of my fuel injectors were partially clogged, causing irregular fuel spray patterns. The total repair in my case involved: Cleaning all fuel injectors, Replacing 2 damaged injectors, Installing a new fuel pressure sensor Final cost was 780 Euro and took about 6 hours of labor. Given your car is showing identical symptoms after a recent service, Id recommend having the fuel injectors tested before replacing the entire fuel pump. Engine stalling and cold start issues often point to injector problems rather than a complete fuel pump failure. Would you mind checking if your fuel pressure readings fluctuate while the engine is running? This could help determine if were dealing with injector issues or a failing pump.

Let me share an update after following up on the suggestions. I had a professional run additional tests focusing on fuel pressure readings. The results showed significant pressure fluctuations while the engine was running, dropping from 58 PSI to 32 PSI intermittently. This testing confirmed that my car performance issues stem from a combination of problems. The automotive diagnosis revealed both failing fuel injectors and a weakening fuel pump. Two injectors showed severe clogging and irregular spray patterns, while the fuel pump was operating at about 60% capacity. This explains the cold start issues and the inconsistent performance. I decided to proceed with a complete overhaul of the fuel system: Replacement of all fuel injectors to ensure balanced performance, Installation of a new fuel pump assembly, Cleaning of the entire fuel system The total repair cost came to 1450 Euro with about 8 hours of labor. While this was more extensive than initially hoped, the car now runs perfectly with no starting issues or rough idling. Fuel consumption has returned to normal levels, and the check engine light has cleared. Looking back, the comprehensive repair was the right choice rather than trying to fix individual components one at a time.