Hello, this is a crosspost from the W205 forum, as I seem to be an individual case and it is not a model-specific problem. I changed spark plugs a few months ago, but I noticed that the spark plug from the 3rd cylinder is significantly blacker (see picture in the appendix). However, the car drives quite normally. Black, dry spark plugs should be a too fat mixture, so injector broken, respectively leaking? The CCs were now the prescribed int 15tkm. Have been original MB candles and have now been replaced with NGK SILZKFR8D7S (probably exactly the same as the original MB, since also “Made in Japan”. What I have done so far: * Ignition coil of 1st and 3rd cylinder replaced. Result: The 3rd cylinder continues to produce a darker spark plug (see second spark plug image) * Compression measurement with Bosch compression tester. All cylinders are between 11 and 13 bar, whereby the 3rd cylinder with 11 Bar delivers the lowest result. I don’t know any more, but I don’t want to change the injector to good luck either. The vehicle is a Mercedes C180 pre-mopf with approx. 66tkm from 2015. Thanks for reading!