TDI A3 8P: Misfire Troubleshooting Guide

Good day.

mein A3 hat einen Verbrennungsaussetzer im 3. Cylinder.
So far, it's just been rough idling and shaking, sometimes more, sometimes less, and sporadically.
The measured flow rate was approximately 2.99 mg/h.
After that, I installed a refurbished fuel injector, but the problem unfortunately persisted, and since then it's been significantly worse: constant misfires, no throttle response, and no power. When I replaced the fuel injector, there was about 100ml of diesel in the cylinder. So, the next idea was to check the wiring harness, suspecting a short circuit that might be constantly activating the injector. I ordered a new one, installed it today, but the problem is still there. The engine isn't losing any oil or coolant, so I've ruled out a crack in the cylinder head.

I hope someone has more ideas about where I could continue my search.

best regards
Lukas.

The BKD is the one with the conical sealing surfaces for the PD elements. Let's see if the sealing surface is oval; you can check the values in the MWB 23 manual beforehand.

"The MWB 23 (fuel injection module) is showing a fault on cylinder 3. I can't provide specific values now because I read the error codes a week ago, and the car won't start anymore. I installed the old PDE (high-pressure fuel injector) hoping that the new/remanufactured one might be faulty or incompatible, but it didn't work. I cleaned the old one in an ultrasonic cleaner beforehand."

The pressure sensors seem to be working correctly... perhaps there's another idea? Could it possibly be related to the OT sensor, so that the control module (MSG) doesn't know when to activate the PDE, or is activating it at the wrong time?

I currently also have a BKD engine in the workshop that I am rebuilding.

Misfires don't always indicate a faulty glow plug. Glow plugs are only rarely seriously defective. The only type of glow plug that fails more often are the piezo glow plugs.

What do both camshafts look like? Could the hydraulic lifters be worn, causing the valves to open only slightly?
What is the compression ratio in the cylinder?

Is the intake manifold carboned up, causing the cylinder to receive insufficient air?

Okay, the camshafts are slightly worn, and the third cylinder was quite full of diesel. I will check the compression and the lifters, etc. During the last start attempts, I got a message saying "Check oil pressure." It might be due to the diluted oil. And thank you for the tips.

It's normal to check the oil pressure when you're trying to start the car and it won't turn over.

I cleaned the injector nozzles again using an ultrasonic cleaner, and I also cleaned the valve seats using a Dremel tool. I used new stretch bolts and vacuumed out any remaining diesel fuel from the cylinder.
After a period of struggling to start, the car finally started. The fuel system probably bled itself, and then it started normally. For the first minute, it still ran poorly, probably because the removed injectors were still cleaning themselves. But then everything was fine. I've driven it for 2,000 km now, and so far, there have been no problems.