Alfa JTD Engine Fix: Quantity Drift Compensation Fix

As someone with moderate experience working on diesel engines, I dealt with a very similar issue on my 2006 Alfa 159 JTD. The symptoms were nearly identical, including rough running and illuminated check engine light with quantity drift compensation errors in the onboard diagnostics. Initially, I thought a simple system reset might fix it, but after taking it to a workshop, they identified a faulty injector that was causing irregular fuel delivery. The repair involved: 1. Complete diagnostic scan 2. Testing all airflow sensors 3. Removing and replacing the defective injection valve 4. Performing a full system reset and injector coding 5. Final calibration of the fuel system The total repair cost was 515 Euro, but it was worth it. After fixing the issue, fuel economy improved significantly and the engine ran smoothly again. To provide more specific advice about your situation, could you share: Current fuel consumption figures, Whether you notice any black smoke, If the problem occurs more during cold starts, When was the last time you had a fuel filter change These details would help determine if your issue matches what I experienced or if it might be something different.

I had my last service at 129680KM and can confirm the problem occurs more during cold starts, with noticeable black smoke. Fuel consumption has increased from 6.5L/100km to around 8L/100km over the past month. The fuel filter was changed during the service two months ago. After reading about drift compensation issues in the onboard diagnostics system, I am leaning towards getting the injectors tested. The degraded fuel economy and cold start problems seem like classic symptoms of injection system problems. Proper performance tuning might be needed beyond just a system reset.

Based on your symptoms, especially the black smoke during cold starts and increased fuel consumption, I am even more convinced our issues were identical. After dealing with my 156 JTD, I learned that these symptoms strongly indicate injector problems rather than just a need for reset procedures. When my fuel injection system was inspected, the technicians found that one injector was not atomizing fuel properly, leading to incomplete combustion. This explains both the black smoke and higher fuel consumption you are experiencing. The performance tuning after my injector replacement included: Precise coding of the new injector, Full calibration of the fuel delivery system, Reset of all related car sensors, Verification of airflow sensors operation My consumption returned to normal (around 6.3L/100km) after the repair. The black smoke disappeared completely, and cold starts became smooth again. The complete fix cost me 490 Euro, but the improved efficiency made it worthwhile. Your description of gradually worsening fuel economy suggests this is not just a calibration issue. I would recommend getting the injectors tested before attempting any reset procedures, as faulty hardware will continue causing problems regardless of software adjustments.

Thanks for the detailed explanation. Those symptoms definitely match what you experienced. I will book the car in next week for a proper injector inspection, as trying a simple reset procedure first would likely just waste time and money. The increase in fuel consumption from 6.5L to 8L/100km, combined with the black smoke during cold starts, makes me confident this is an injector issue affecting the fuel injection system. The onboard diagnostics pointing to drift compensation problems further confirms this diagnosis. I appreciate knowing the full repair including new injectors, coding and car sensors calibration came to around 490 Euro in your case. This helps set my expectations for the upcoming workshop visit. Hopefully once fixed I will see my fuel economy return to normal levels too. I will update the forum once I have the results from the inspection and know exactly which repairs were needed to resolve the rough running issues. This kind of specific technical information really helps others facing similar problems.