Smart Fortwo Diesel: Turbo Boost Issues Killing Power

Had very similar issues with a Smart Fortwo 2016 diesel. Coming from someone with moderate experience working on turbo diesels, the symptoms match exactly what I encountered, poor acceleration, increased fuel consumption and that annoying check engine light. After initial diagnosis, the workshop found a vacuum leak caused by a faulty vacuum switching valve connected to the boost solenoid. The pressure sensor readings were all over the place, which explained the erratic boost behavior and engine performance issues. The fix involved replacing the vacuum switching valve and checking the intake manifold connections. Total repair cost was 140€ including parts and labor. Since then, the boost control has been working perfectly and fuel economy returned to normal. Before suggesting specific fixes, could you share: Current mileage? Any recent repairs or maintenance? Whether the check engine light stays on constantly or flickers? If there are any whistling sounds under acceleration? This information would help determine if your issue is identical to what I experienced. Bad vacuum lines or faulty boost control components often show similar symptoms, but its best to confirm with your specific vehicle details.

Thanks for your detailed insight. My car has 72232 KM on the clock, with the last major service completed 3 months ago. The check engine light stays on constantly without flickering. There is a faint whistling noise under heavy acceleration, especially noticeable between 2000-3000 RPM. The poor engine performance and turbo lag are most noticeable when trying to overtake or climb hills. Based on your experience, it does sound very similar to a vacuum leak situation. Did your workshop perform any specific diagnostic tests before concluding it was the vacuum switching valve? Looking to get this sorted quickly as the increased fuel consumption is becoming costly.

Your symptoms are remarkably similar to what I experienced, particularly that whistling noise between 2000-3000 RPM. The workshop used a smoke test to confirm the vacuum leak in my case, which clearly showed the faulty connection at the vacuum switching valve. The pressure sensor readings during diagnostics indicated unstable boost pressure, fluctuating well below normal operating values. This directly affected engine performance, especially during those crucial overtaking moments. One additional test they performed was checking the intake manifold pressure under load, which revealed inconsistent readings, another telltale sign of boost control issues. The vacuum leak was allowing unmetered air to enter the system, confusing the engine management and causing the poor performance. Given your mileage is similar to when my issue occurred, and considering the constant check engine light combined with that specific whistling noise, I strongly suspect you are dealing with the same vacuum leak scenario. The boost solenoid control system is quite sensitive to any vacuum irregularities. When you do take it to the shop, request a smoke test specifically, it was the quickest way to pinpoint the exact location of the leak in my case. The total diagnostic time was about 1 hour before they identified the failing components.

Thanks for the insights. After reading through the responses, I will definitely ask for a smoke test when I take it to the shop. The similarities between my symptoms and what others experienced with vacuum leaks affecting the boost control system are striking, especially that specific whistling noise between 2000-3000 RPM. I have booked an appointment with a local workshop that specializes in turbo diagnostics. Will ask them to check the vacuum switching valve and boost solenoid connections first, since these seem to be common failure points. Also requested they inspect the intake manifold pressure under load conditions to rule out any other boost controller issues. The car is due for its annual inspection soon anyway, so this is a good time to get the compressor surge and pressure drop issues sorted. Will update the thread once I have the diagnosis and repair results. Really hoping it turns out to be just a vacuum leak like the other cases described here. Based on the feedback, I am much more confident now about what to expect and what to ask the technicians to check specifically. Much appreciated!