Misfire/ Knocking sound C63 W205

[onuris]

Hi guys,



I have finally come to this forum after exploring all the knowledge from my local MB Garage. I have to say I am complete layman but I will share the things that I have done to try and deal with this issue.


Little background to the vehicle:

Bought the car in 2021 and on the way home the engine light came home and this is where the misfire dilemma started. After initially consulting a local tuner, we found out that the vehicle has had a stage 2 remap done to it and various other mods such as downpipe, sportscat, and a valved aftermarket exhaust.

Since then the journey began to figure where the issue lies. Starting with changing all spark plugs, moving coil packs from one bank to the other (fault didn't move) and a cylinder compression test (which was ok). We removed the map and put the car back to stock (latest software update) and the misfire seemed to have gone. It didn't misfire in idle anymore but after a couple of days the engine light came back and the misfire still seemed to have gone, but occasionally I could hear a knocking sound in idle (video 1). So I went back to my local Merc specialist and he assumed it would be issues with the cats but after taking them off, the issue seems not to be that either. Instead they found a part which they couldn't identify what it was for either (video 2).

This is the knowledge I have so far, I hope someone could help me how to resolve this issue. The local Merc specialist told me that the car is too modified for them to continue any further..


video 1

video 2


Many thanks!

 

[Uncle Benz]

Hmm. The lambda sensor after the catalyst has a spacer tube on it so that it doesn’t detect the excess hydrocarbons that the sports cat cannot remove. This messes with the tuning big time. Honestly, it looks a mess. I wouldn’t like to get involved with it, but short of returning it completely to standard I’d recommend you give Anthony at GAD tuning a call, see what he thinks. He’s tuned a lot of these engines and might have some clever ideas.

 

[alexanderfoti]

That hard misfire on the first video doesn't sound great. Its worth further investigation to see if its a plug/injector. The fact you have 2 hard misfire codes across separate cylinders warrants a closer look at the cylinders etc.

The car has sports cats fitted, so maybe indicates a hard life. Not a great shout that the tuner couldn't disable o2 sensor check, and instead chose to use the spacers, as above. May indicate its been tuned bady, or not at all etc?