AFN is annoyed: TDI timing?

Hello.

"I have a Galaxy, manufactured in 1998 (1.9 TDI, with variable valve timing, engine code AFN). After a major engine failure, I installed a new engine, which ran well for the first 500 km. Then, it started to have difficulty starting, gradually getting worse until it wouldn't start at all, of course, in the middle of nowhere. The workshop said the timing pulley on the crankshaft was worn out and replaced it, along with the timing belt. After readjusting the fuel injection pump, it then started running again." A few weeks later, I checked the injection timing using VAG-COM, and it was roughly between the middle and lower lines.

Since the day before yesterday, the thing has been starting worse and worse, especially when it's cold. The fuel consumption isn't particularly high, and the engine runs smoothly, but it smokes quite a lot, especially under load.

The TDI graph is no longer displaying any data: while it does measure the fuel temperature, it always shows "0" for the timing.

Now I'm wondering if something is wrong with the timing belt again, or if maybe it's just a faulty sensor. The cables seem to be properly connected, and VAG-COM also displays values related to injection timing when browsing through the menus.

Do you have any idea what that might be?
Can anyone provide me with comparison values for injection timing, injection quantity, etc. for this engine, so that I can check them using VAG-COM?

Thank you in advance!