In the fs2020, the engine behavior of the DA40 TDI is like a naturally aspirated engine. The critical engine altitude is supposed to be much higher than an atmospheric engine. Also the transfer pump is not working.
I’m unsure of the Critical Altitude RPM, but the transfer pump works for me. It takes a while to see results, but it works. Seems to initially use left tank fuel and then when activated, the pump will draw from the right tank to replenish the left. It looks like an arrow above the switch is pointing to the left, so maybe that’s the intended operation. I think that isn’t the best way to use both tanks, but I monitor the levels and use the transfer to try to maintain some left-right weight balance.
In my case, the DA40 NG works good, but not the DA40 TDI, the analog panel version and with a different engine than the DA40 NG.