Audi A5 Fuel System Nightmare: Loss of Power & Smoke

Having dealt with nearly identical symptoms on my Audi A4 2017 petrol engine, I can share my experience. After experiencing similar issues with fuel consumption and engine performance, I took it to a workshop where they diagnosed the problem. The root cause was a faulty wiring connection to the fuel injection system. The damaged cables were causing inconsistent signals, leading to improper fuel delivery and the symptoms you described. The repair involved replacing the wiring harness and checking all related plug connections. The total cost was 95 Euro for parts and labor. The maintenance was fairly straightforward once properly diagnosed. Before the fix, the engine would struggle particularly during acceleration, and the excessive fuel consumption was quite noticeable. The smoke from the exhaust was a clear sign of the system not functioning correctly. To provide more specific guidance, could you share: Current mileage, Any warning lights on the dashboard, When was your last fuel system maintenance, Type of fuel you typically use This information would help determine if your issue is similar to what I experienced or if it might be something else in the engine system.

Thanks for sharing your experience. My current mileage is 66017 KM and last fuel system maintenance was performed during the regular service 3 months ago. No warning lights are currently showing on the dashboard. I use premium unleaded petrol as recommended by the manufacturer. The performance issues started gradually, but now the fuel consumption has increased by about 25%. The smoke from the exhaust appears mostly during cold starts. Hearing about your wiring issue makes sense, as the symptoms match quite closely with what I am experiencing. 95 Euro seems like a reasonable repair cost if that turns out to be the problem.

Thanks for providing those details. Looking back at my experience, your symptoms are even more similar to what I encountered than I initially thought. The gradual onset and the 25% increase in fuel consumption matches exactly what happened with my A4. The cold start smoke is particularly telling, this was also a key symptom in my case. Since your fuel system maintenance was done recently, and there are no warning lights, this further supports the likelihood of a wiring issue affecting the system performance. In my case, the regular diagnostics initially missed the problem because the wiring fault was intermittent, which explains the lack of warning lights. The premium fuel usage rules out any fuel quality issues. My repair actually revealed that the wiring insulation had deteriorated where the harness bends near the injection system, causing inconsistent electrical signals to the fuel injectors. This explained why the engine performance would vary and why the air-fuel mixture was occasionally too rich, causing the smoke. One quick check you can do: listen for any slight clicking sounds from the injectors at idle. In my case, the rhythm was notably irregular before the repair, though this might be hard to notice without a comparison. Would suggest getting the wiring connections checked first before exploring more complex fuel system issues, as this could save both time and money in the diagnostic process.

Thanks for all that detailed input. I will definitely get the wiring connections checked first, given how closely my symptoms match your experience. The clicking sound tip is particularly helpful, I just went to check and noticed the idle does sound somewhat irregular compared to when the car was running normally. The gradual onset of issues and similar petrol consumption increase really does point to an electrical system problem rather than a mechanical one. After looking at the maintenance records, I noticed the fuel system check during the last service was mainly focused on the mechanical components, so they might have missed any developing wiring issues. I will schedule an appointment to have the wiring harness and connections inspected, particularly around the injection system area you mentioned. The 95 Euro repair cost would be a relief compared to what I was worried might be needed for a complete fuel system overhaul. If this turns out to be the same issue, the air-fuel mixture problems you described would explain both the cold start smoke and the engine performance issues I am experiencing. Will update once I get it checked out.