Mercedes GLS problems with misfiring for some time now

Hey, I had a similar problem with my 2019 Mercedes GLE. In my case, it was actually the engine control unit (ECU) that was defective. The symptoms were very similar: black smoke, check engine light, jerking and high vibrations. I only have a little experience with cars, so I went straight to the garage. They did a thorough diagnosis and found out that the engine control unit needed to be replaced. It cost me around 1000 euros in total. If you give me more information about your vehicle, I might be able to help in more detail. Which engine exactly? Have you already read out an error code? Best regards

(Translated from German)

Hey, thanks for the quick reply! I have read out the error code P0304, which indicates misfiring in the fourth cylinder. Last service was at 90,000 km, now I'm at 96,543 km. Maybe the ignition coil after all? Have you had similar error codes? Best regards

(Translated from German)

Hey, yes, fault code P0304 definitely indicates misfiring in the fourth cylinder. In my case, it was error code P0302, i.e. misfiring in the second cylinder. As I said, in the end the engine control unit had to be replaced. However, I still wouldn't rule out the ignition coil, especially if you've only recently had it serviced. It also helps to check the spark plugs - sometimes the problem lies there too. A defective spark plug connector could also be the reason. Another thing you could do is swap the ignition coil from the fourth cylinder with another one and see if the fault moves with it. If the fault then moves to another cylinder, you know for sure that it is the ignition coil. If nothing helps, I would go back to the workshop and have the diagnosis confirmed. It's better to spend a few euros on a thorough check than to have more expensive repairs later. I hope this helps you! Best regards

(Translated from German)

Great, thanks for the tips! I will definitely try replacing the ignition coils and check the spark plugs at the same time. It sounds like a more sensible approach before I start looking at the engine control unit. Let's see if this can localize the problem. If not, I'll probably have to go to the garage after all to avoid more expensive repairs. I'll get back to you when I have an update. Thanks again and best regards!

(Translated from German)