Smart Fortwo Diesel Stalling: Fuel Mix Issue Alert

I had a similar issue with my 2015 Smart Forfour diesel and understand your concern about the fuel system. With some basic car repair experience, I initially thought it was contaminated fuel affecting the fuel mixture, but it turned out to be simpler. The symptoms matched exactly what you describe, check engine light, stalling at idle, and error codes. After taking it to my regular workshop, they diagnosed a loose connection in the fuel system sensor wiring. The cable connection to the fuel mixture sensor had deteriorated, causing incorrect readings in the combustion chamber. The fix was straightforward, they repaired the connection and cleared the codes. Total cost was 95€, much cheaper than the complete fuel system flush I initially feared would be needed. The car has run perfectly since then. Before suggesting more specific solutions, could you share: What error codes are you getting? Did this start right after refueling? Have you noticed any changes in fuel consumption? Are there any unusual sounds from the fuel pump? This would help determine if your issue is electrical like mine or actually related to fuel quality. Sometimes fuel additives can help, but lets first identify the exact cause.

Thanks for the feedback. My stored error codes are P0171 and P1128, which point toward a lean fuel mixture issue. Yes, problems started after refueling at an unfamiliar station. Last service was completed at 180000 KM with new fuel filter installed. The engine knock has become more noticeable, particularly during cold starts. Fuel consumption increased about 15% over the past week. No unusual sounds from the fuel pump area, but there is some hesitation during acceleration. Running some fuel system cleaner through the next tank might help if its contaminated fuel. Though given the symptoms, I may need a proper fuel system inspection to rule out other issues affecting the fuel mixture.

Thanks for those details, especially about the error codes and fuel consumption increase. After you mentioned the knock during cold starts, it reminded me exactly of what happened next with my Smart Forfour. Initially, I also tried a fuel additive treatment thinking it would solve the lean mixture issue, but the problems persisted. When the workshop did a thorough inspection, they found that fuel contamination had actually damaged the high-pressure fuel pump. The incorrect fuel composition had caused scoring inside the pump housing. The complete repair involved: Draining contaminated fuel, Replacing the high-pressure fuel pump, Installing a new fuel filter, Full system flush, Reset of engine management codes Total repair cost was 780€, but it completely resolved both the fuel economy issues and engine knock. No problems in the 40000 KM since the repair. For your case, the P0171 code combined with increased fuel consumption strongly suggests a similar fuel system issue. While fuel additives might help in mild cases, the cold start knock indicates potential pump damage. Would recommend getting it checked soon before it potentially affects other components. Your symptoms align perfectly with my experience, its worth getting a proper diagnosis rather than risk running compromised fuel through the system any longer.

Thanks for your detailed explanation. Got the same codes P0171 and P1128, and definitely seeing similar behavior with the engine knock at cold starts. The fuel consumption spike matches what you experienced too. Makes sense about the high-pressure fuel pump potentially being damaged by fuel contamination. Given how the symptoms match your case and the fact my issues also started right after refueling, I should probably skip experimenting with fuel additives and get it properly inspected. Rather than risk more damage to the fuel system and combustion chamber components, I will book it in for a full diagnosis. The 780€ repair cost you mentioned is steep but sounds worth it compared to letting the problem get worse. Will try to get it looked at this week. Good to know your repair has held up well over 40000 KM, gives me confidence that getting it fixed properly the first time is the right approach. Thanks for sharing your experience with such specific details about the repair process.