Hello Mercedes and AMG fans,
I would like to thank you for lots of the information which I can find in here, so I would like to share with you our story of the diagnostic and repair of C32 AMG ( M112 W203). Why did I make this thread?
There are a lot of threads like “misfire issue” etc. without the solution.
We gathered lots of information and inspiration from various threads.
We learned it the easy way compared to some of you who learned in the most difficult way, so we want to give you some information in return.

Few more words:
I write “we” this means me and my brother.
Even if I am able to handle english somehow (well i hope at least) it is not my primary language and my car vocabulary is quite limited.
This topic might be long, but I want to give you as much information as possible.
This whole topic will be copy pasted to different forums since we gathered information from various forums.

The story
1) Few weeks ago we found a C32 T AMG black combi for a great price. It has some minor defects (some corrosion, noisy tires, resonance low frequency noise) but the main issue was described like this:”At full throttle, around the 4-5k rpm engines disconnect 2 cylinders and switch to safe mode”. We asked for the screenshot from the diagnostic and we got:
P2050 - Misfiring, Damages TWC
P2052 - misfire on cylinder 4,
P2056 - misfire on cylinder 5
We asked what the seller tried and did and we got the following information: “My technician made a check and was not able to recognize where the issue is coming from. He checked compression in pistons and it was OK. He also switched coils from different car and had the same issue”. We negotiated and decided to risk it.

2) We brought the car back to our workshop and started to look for the solution. The most of the threads and advice were in the Bermuda Triangle sparks-coils-wires. We checked local suppliers and we decided to change all 3 suspicious subjects (price of the 12 sparks, set of the coils and set of the cables were around 300€) to exclude any possible sporadic issue. This looked like a most likely root cause, we were quite confident. We were wrong. We switched parts, removed error with Delphi diagnostic and no change. Still same issue.

3) We let a few days sit and thought about that. Additional ideas for root cause were various - faulty engine, faulty ECU, faulty pistons, faulty exhaust,... Tested it in the car multiple times, etc. Then my brother decided to make a proper diagnosis. He loaded errors from the ECU and there was lots of them:
P2050 - Misfiring, Damages TWC
P2052 - misfire on cylinder 4
P2054 - misfire on cylinder 6
P2056 - misfire on cylinder 5
P2051 - misfire on cylinder 1
P2055 - misfire on cylinder 2
P2043 - multiple misfires on multiple cylinders
(sorry if the description is not correct, we have diagnostic tool in native language)
Delete errors and push car to safe mode again, errors:
P2050,P2054,P2056
and again
P2050,P2054,P2056
and again
P2050,P2052,P2056
and again…
P2050,P2052,P2056
and again…
P2050,P2052,P2056
and again last one
P2050,P2056
He also discovered that this issue is NOT connected directly to the RPM but to the load since when you accelerate by 30%, this issue will not appear, only during the heavy load/full throttle. We discovered that this issue appears 100% on cylinder 5 and sometimes on cyl 4 and 6.
This picture helped us to recognize that this issue appear only on 1 side of the engine, or 1 side of the engine is affected more by this issue


4) So what's next?
Engine itself looks ok and symptoms does not show any signatures of damage (smoke looks fine, can run in high rpm, before cylinders are disconnected no signatures of an issue)
There is no visible or smell of oil leakage nor the coolant leakage.
Visual and sound check from the top seems to be OK, let's make the visual check from the bottom. We put the car on the lift and started to check the bottom of the car. No leakage, everything looked normal. We started to try the differences between the left and the right sides.

5) And we were able to find some differences. During the check of the exhaust, we were able to detect differences on the exhaust


I am not able to probably name and explain all parts directly, so I will put this colour picture to explain. We discovered that there are new bolts near the green part, the green part is completely missing for some reason. During the inspecting exhaust for the holes, we discovered non-factory welding in red-purple and blue-purple areas. This purple-welded side is that one with the issue. So the exhaust was modified for some reason (corrosion? tuning?) and somebody made/checked something on the affected side. We removed lambda sensors and with the endoscope checked red catalytic converters on both sides to see if there are any differences.

Well, there were some minor differences, but both of them are completely empty.. Based on this we decided to unmount the whole exhaust, check if there is no contamination which can cause issues and check for lambda sensors.
6) When we checked red empty catalytic converters, lambda sensors, we cleaned pipes with pressed air. During the cleaning, we still focused on the left vs right side differences.. and we were able to see that there is significant difference between air flow through blue catalytic converters. We tried to push more air and clean them, but they were clogged. We were not able to estimate if the air flow was ok or not, but there was a significant difference. During the discussion we decided to remove them and replace them with pipes and test it. No more teasing - IT WORKED! Blue catalytic converters were apparently clogged (on affected side completely, second side paritaly)

Currently the car is running temporarily without the blue cats for testing purposes for a few days without the single issue. Car gains SIGNIFICANTLY more power (we are able to feel those 350hp finally) and there is no issue with the misfires nor the cylinder disconnects.
Congrats to everybody who read this topic. Good luck with solving this issue the easy way as we did and enjoy the car. I am probably not going to follow this topic/thread so in case of any question, you can contact us http://fb.com/autosluzbyhk.cz - both of us has access to this FB page and we can answer to you.

 

so unusually the issue was with cats.
how much km has the car on odometer?
are there some budget verions of the cats available for c32 amg?

 

I had the same issue. Please check if you’re losing coolant as well, because in my case the root cause for the failing cats was a leaking intercooler.

 

Car has 240k km. Based on the service history looks legit. I did not check for the cats yet, Iam still not decided how to solve it (full custom exhaust, rebuild stock,..)


Thanks you for the advice! Yes, we are going to check it,thanks!

 

My car had one cat blown completely through and ran perfectly fine. Instead of fixing them I just removed all the cats lol

 

That's awesome.

And how did you pass the emission test cycle, could you share the certificate with your values ?

 

Emission test? What is that? I live in Florida, you could register a straight piped refrigerator with 4 wheels and nobody would bat an eye.

 

me volví loco con ese problema cambie todo el sistema de encendido, bobinas,cables,bujias,sondas,escape nuevo,inyectores,sensores,bomba de gasolina,mariposa, y el fallo seguía ahí P2055 cilindro 2 debido a tanta rompedura de cabeza lleve el coche a un taller muy especializado y alfin me dijeron que el catalizador derecho está jodido!! Mi pregunta es alguien sabe si hay alguna manera de repararlos?? O se deberían remplazar gracias de antemano