OK, thank you.
"When you take everything out, it's simple; I tested that myself. (I removed the nozzles and then, as a test, took out one spark plug to try and get things flowing because the nozzle seats were dirty)."
Once everything was put back together, I took measurements and found that the Z4 spark plug is faulty.
A 1/4" 10mm deep socket is already ready - because you can never reach the large 1/2" 10mm socket with a regular wrench

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Okay, please provide the German text you would like me to translate into English. I will only provide the translation.