Smart Forfour Diesel: Rough Running + Low Power Issues

I had nearly identical symptoms with my Smart Fortwo CDI 2008. The rough running and weak acceleration turned out to be failing fuel injectors. The check engine light came on because the engine was running extremely lean, which was spot on with what your mechanic suggested. The diagnosis showed carbon deposits had built up in the injectors, preventing proper fuel atomization. This affected the fuel-air mixture, leading to poor performance and the jerking sensation during acceleration. The faulty fuel injectors were also causing uneven fuel distribution, which explained the rough running. This was a serious issue that needed immediate attention since running too lean can potentially damage other engine components like the catalytic converter. The oxygen sensor readings confirmed the lean condition. The repair involved removing and testing all fuel injectors, which revealed two were severely clogged and one had electrical issues. The throttle body was also cleaned during this service since it had carbon buildup, though this was secondary to the main injector problem. Getting a proper diagnosis with specialized diagnostic equipment is crucial. The symptoms you describe strongly point to fuel delivery issues, which typically means problematic fuel injectors in these engines.

Thanks for sharing your experience. This sounds exactly like my problem. The jerking and weak acceleration was driving me crazy before I got it fixed. The check engine light kept coming on, and like you, my engine was running pretty rough. My fuel injectors were also the culprit, along with a clogged EGR valve that was making things worse. After getting those sorted, the engine performance went back to normal and the check engine light finally stayed off. Do you remember roughly how much the repair cost in your case? Also, have you had any similar issues pop up since getting it fixed?

Those injector issues can definitely cause headaches! Just got mine fixed last week, total bill came to 515€ for replacing the faulty injector. The mass air flow sensor readings are now perfect and the check engine light has stayed off. The engine is running much better now that the air-fuel ratio is correct. No more lean condition showing up on diagnostics, and the oxygen sensor data confirms everything is working as it should. The rough running and jerking completely disappeared after the repair. Since fixing the injector, the car pulls strong and smooth through all gears. The catalytic converter was thankfully not damaged from the lean condition. Its been about 250km of trouble-free driving so far. To prevent future issues, Im using high-quality fuel and following the recommended service intervals strictly. Running lean can cause serious engine damage if left unchecked for too long.

After dealing with this frustrating issue, I finally got it sorted at my local garage. The total repair came to 680€, a bit more than yours since they had to clean both the injectors and fix that clogged EGR valve. Still, considering how badly the engine was running, it was worth every cent. The mechanic showed me how dirty the injectors were, no wonder the air-fuel ratio was so far off. Since the repair three months ago, Ive put on about 5000km with zero issues. The engine runs like new, no more jerking or rough idling, and thankfully the check engine light has stayed off. One thing I learned is how important it is to catch these problems early. Running lean could have damaged my spark plugs or worse. Now Im really careful about using good quality fuel and sticking to the maintenance schedule. Thanks again for helping me understand what was going on with my car.