AVF Cold Start: Troubleshooting & Solutions

Hello from Verona, I'm having another problem... Passat 3B6, manufactured in 2005, engine AVF. It's difficult to start sometimes, especially after a longer period of inactivity. It seems like there's air in the fuel. Here's some information: The fuel pump in the tank is new. When starting, it runs continuously at 0.4 bar. The fuel lines are okay. The fuel filter is new. The return valve is new. The tandem pump has been replaced and checked according to Elsa. The PD injection timing is 330-370 degrees (starter motor), with an injection duration of 30ms. The injection angle during cold start is approximately 12 degrees. The error memory is clear. The compression is 30 bar. The fuel system has been purged with 5051, but the combustion chambers still remain dry. The only thing that seems to help is to block the return flow, then the car starts slowly and runs like a beast. Does anyone know how the fuel pressure in the cylinder head is built up or regulated (3-7.5 bar?)? Is it only from the tandem pump? Thank you very much from Italy.

Hmm, things are getting increasingly complicated with all the new stuff.

I would have guessed it was a tandem pump.
It would be interesting to see if the fuel pressure fluctuates by more than 0.2 bar when the engine is running at idle, 1500 rpm, or 4000 rpm. If it does, then you've likely identified one of the faulty pumps.