Smart Forfour Misfire: Bad Coil Pack Warning Signs

I had an almost identical issue with my Smart Fortwo 2012 gasoline model last winter. With some experience working on these engines, I can tell you engine hesitation and rough running are common symptoms of coil failure in these models. My car showed the same signs, rough idle, jerking during acceleration, and the engine warning light. Initially thought it was spark plugs, but vehicle diagnostics pointed to a coil pack issue. The real problem turned out to be damaged wiring near the coil connector that was causing intermittent connection issues. The repair involved replacing the damaged wiring and connectors, which cost 95€ in total. After fixing the connection, the engine hesitation completely disappeared and it has been running smoothly since. However, to provide more specific advice for your case, could you share: Have you noticed if the issue gets worse when the engine is warm? Does the misfire happen more frequently at specific RPM ranges? Have you already had the error codes read from the engine computer? When was the last time your spark plugs were changed? These details would help determine if your symptoms match the same ignition coil related problems I experienced.

Thanks for the previous responses. Just wanted to mention my car has 176300KM and spark plugs were replaced during the last service 4 months ago. About the engine hesitation, it definitely gets worse when warm, especially above 2500 RPM. The check engine light started flashing occasionally during acceleration. The misfire seems most noticeable during highway driving. My mechanic pulled the error codes showing cylinder 2 misfire. Given the recent spark plug change, the coil pack theory makes sense. Good to hear a similar issue was resolved on your car, though I will have them check the wiring connections too before just replacing parts.

Thanks for those additional details about your Smart Forfour. Those symptoms match exactly what I experienced with my 2012 Fortwo, especially the worsening misfire above 2500 RPM when warm. After seeing your mileage and getting confirmation about the recent spark plug change, I am even more convinced you are dealing with a failing coil pack. The flashing check engine light during acceleration is a telltale sign of severe misfire, which perfectly matches coil failure symptoms. My misfire also started showing up more during highway speeds, just like yours. The cylinder 2 error code is significant, in my case, the damaged wiring was causing the coil pack for that specific cylinder to fail intermittently when hot. Since your car has higher mileage, I would actually recommend replacing the coil pack rather than just checking connections. While my issue was wiring-related, at your mileage the coil itself is likely worn out. Engine hesitation and misfires typically get worse with heat when the coil is failing internally. Consider replacing all coil packs as preventive maintenance, in my case, the second coil started showing signs of failure about 6 months after fixing the first one. The complete coil pack replacement cost me 280€ including labor.

Great info everyone. Based on all the responses and my own ongoing issues, I think I will proceed with replacing the coil packs on my Forfour. The matching symptoms, especially the heat-related misfire and engine stalling, are too similar to ignore. My mechanic quoted 320€ for replacing all coil packs, which seems reasonable compared to the prices mentioned. Given the vehicle diagnostics results showing cylinder 2 misfire and my high mileage, doing all of them makes sense as preventive maintenance. Will make sure they inspect the wiring and connectors during the repair too, since that could be contributing to the coil failure. Really hoping this resolves the rough running and acceleration issues completely. The constant engine hesitation during highway driving has been quite stressful. Will update once the work is done to confirm if this fixed the problem. Thanks for helping confirm my mechanics initial diagnosis about the ignition system issues.