Audi S8 Engine Stalling: Fuel System Likely Culprit

Experienced similar issues on my 2003 Audi A8 with the 4.2L engine. The symptoms match what turned out to be a failing fuel system problem in my case. The main signs were identical, stalling at idle and persistent check engine light. Initial fuel quality tests showed no contamination, but the real problem was traced to deteriorated wiring at the fuel pump connector. The connection had corroded over time, causing irregular fuel delivery and engine performance issues. The repair involved replacing the entire fuel pump assembly because the wiring harness was integrated. This was a serious repair since the fuel tank needed to be dropped to access the components. If left unchecked, it could have led to complete fuel system failure. Worth checking the fuel filter first, as clogged filters can create similar symptoms. But given the age of your S8, the electrical connections to the fuel pump should be inspected. Engine knock can develop if the fuel supply becomes irregular due to faulty connections. Would recommend getting a specialized fuel system diagnostic done. The stalling issue typically worsens over time if electrical connections are the root cause.

Thanks for sharing your experience with the fuel pump assembly issue. My mechanic just completed the repair last week and I am curious how yours has been holding up. The stalling problems have disappeared completely after replacing the fuel pump and cleaning the fuel system. The engine runs much smoother now and fuel economy has actually improved a bit too. Can you share what the total repair cost was in your case? Mine was fairly expensive since they had to drop the tank. Also wondering if you have had any other fuel system related problems pop up since the repair?

Great to hear your fuel system issues were resolved. Since my last post, I can confirm my repair has been completely reliable with no recurring problems. The fuel quality and delivery have remained consistent, with no signs of fuel contamination or irregular engine performance. The initial repair bill in my case was just 95 Euro, since it turned out to be only a faulty cable connection at the fuel pump, much simpler than expected. No need to drop the tank completely. Once the mechanic identified the incorrect fuel composition was due to the electrical issue, the fix was straightforward. The fuel system has been running flawlessly for months now. No check engine lights, no stalling, and the engine idles perfectly. Regular use of fuel additives as preventive maintenance has helped keep the system clean. The fuel filter is still performing well, but I plan to replace it during the next scheduled service as a precaution. Your repair sounds more extensive than mine was, but the investment seems worth it given the improved performance you're experiencing. A properly functioning fuel system is crucial for engine longevity.

Found a reputable performance shop that specializes in Audi fuel system repairs. The techs diagnosed the issue properly, exactly what you mentioned about the wiring harness being damaged. Total repair came to 850 Euro which included dropping the tank, new fuel pump assembly, and a complete fuel system cleaning. The improvement in performance has been remarkable. No more stalling issues, smoother idle, and better fuel economy overall. The combustion chamber is getting proper fuel delivery now. Really glad I addressed it before any serious engine damage occurred. Have put about 2000km on it since the repair with zero problems. The shop recommended changing the fuel filter in another 5000km as preventive maintenance to avoid any wrong fuel mixture issues down the road. Will definitely stay on top of that. Thanks again for pointing me in the right direction with the electrical connections. Saved me from going through multiple failed diagnosis attempts at other shops that might have missed the root cause.