Audi S4 B8, engine code CAKA, misfire P0303

Good day, fellow DIY enthusiasts.
This is my first post here in the forum .
I'm having a problem with my Audi S4.
Since Friday, the EPC (Electronic Power Control) light and the engine check light have been on in my car. The engine runs unevenly when idling, but the engine runs smoothly again at higher RPMs (above 1300 RPM).
Error code stored in the control unit:
6352 - Cylinder 3
P0303 00 (237) Misfire detected.
Warning light ON - confirmed - checked since last reset.
Error frequency: 1.
Motor speed: 696 RPM.

I then cleared the error and restarted the vehicle. The error is still there.
I then logged the misfire data for cylinder 3 through the measurement blocks, and the number quickly jumped from 237, but then remained at that value.
I'm relatively sure that the problem is with the fuel injector for cylinder 3.
This weekend, I looked into the error and checked the following things:
The spark plugs are new and have been swapped, with the one from cylinder 2 moved to another cylinder. The ignition coils have also been swapped. The error remains the same.
The oil separator/crankcase ventilation system (whatever you want to call it) was also recently replaced -> it was replaced as part of routine maintenance, but I've read online that it can also cause misfires.
Some people wrote online that the cat (likely referring to a catalytic converter) was clogged, but I rule that out because only one cylinder is misfiring, not the entire bank.
I'm hoping for some valuable insights that either confirm my suspicions or point to other things I could investigate.

Best regards and thank you for the answers.

Hello,

A complete car scan is always helpful. You've already checked the ignition coils, haven't you? Hopefully, you've replaced the spark plugs.

If so, I would suggest a compression test to rule out any mechanical problems.

Best regards, Rainer.

How many kilometers has the car been driven? Have you measured the compression yet?

Danke für die schnellen Antworten!
I haven't checked the compression yet because I don't have the necessary tools, but I will order them now and then check the compression.
My initial thought was to remove the fuel injectors, and I've already ordered the tool for that.
So that I can have them cleaned or possibly order new ones.
I've noticed something: theoretically, if nothing is being injected, the lambda sensor should register an error, indicating a lean mixture or something like that.

The S4 has 234,000 km (approximately 145,000 miles) but has been very well maintained with regular servicing.
And the mentioned error here is the only one that appears; otherwise, there are no other entries in the log.

Sincerely,

Please enable the Autoscan feature.

If you suspect the fuel injector, I would recommend logging the fuel injection quantity. Analyze the data as much as possible without replacing or disassembling any components.

Here's the Autoscan I mentioned.
Thank you for your help.

I also checked the valves using the actuator diagnostics. Valves 1-6 are clicking evenly and all are functioning correctly.
Therefore, I suspect that the nozzles are clogged, even though the function is still ensured.

I was unable to log the fuel injection amount because I couldn't find the measurement values for it...

Indeed, coking could be a problem, and an initial BEDI cleaning might solve your issue.

"However, I recommend analyzing the situation before starting any (unnecessary) actions. Try to find the fuel injection logging data again. It might provide further clues."

This morning, I had some time and wasn't patient, so I removed all the injectors. Some of them have significant deposits, but I'm soaking them in injector cleaner overnight (just to the tip, where there's carbon buildup). I didn't want to start the engine again with what I thought were clogged injectors.
I will keep you updated when these are reinstalled.

Please include pictures.

Good day.

Update: Einspritzdüsen gereinigt. Beim Einbau habe ich die Einspritzdüsen 2 und 3 getauscht und nach der Fertigstellung des Einbaus, den Motor gestartet und leider ist der Fehler weiterhin vorhanden.
Unfortunately, the problem persists with cylinder 3. The error remains specifically with cylinder 3, even after replacing the injectors.
As the next step, I will measure the compression of cylinder 3.

Best regards,

B4cklink wrote:

Unfortunately, the problem persists with cylinder 3. The error remains specifically with cylinder 3, even after replacing the injectors. My next step will be to measure the compression of cylinder 3.

That's exactly what I meant by "analyzing"... You probably have a Generation 2 or 3 TSI engine. The issue with the piston rings is well-known in these engines.

Specifically, I would inspect damaged piston walls/pistons using an endoscope. Furthermore, any cracks in the connecting rod or bearing damage must be investigated further.

I will remember your tip for the future .
I will also perform an endoscopic examination of the combustion chamber.
Thank you for your help.

Good day, fellow DIY enthusiasts.

Cylinder 3 had no compression.
Well, unfortunately, I couldn't see anything during the endoscopy at that time.
So, I decided to remove the engine myself and try to find the problem.
Once the engine was removed and the cylinder head of the affected bank was taken off, a burnt-out valve quickly became visible.
Fortunately, the cylinder walls of all cylinders are in good condition; you can even still see the cross-hatch pattern.

Now I've ordered many new parts, and I'm partly glad I took this step because it will allow this engine to last much longer.

I just wanted to give you a quick end-of-day update.

Thank you for the feedback!