MFA: 3x Higher Than Average Consumption

Hello everyone.

I bought a Passat 35i, model year 1992. It has been modified with a 1.9 TDI engine (engine code: 1Z), which is approved by VW. It's working well overall, but the MFA (Multi-Function Display) shows an average fuel consumption of 18-22 liters per 100 km. The actual fuel consumption is 6.72 liters per 100 km, according to the last fuel tank reading.
Can anyone give me a hint about what's ahead?

The speedometer is from a 2.0L 16V gasoline car. There's also this vacuum transducer still connected at the back, which was previously used for the MFA. Could it be related to that?

Hello,

The instrument cluster (likely from the 1992 model year?) is not yet diagnosable. Therefore, you cannot fix it by reprogramming (which is not possible with newer instrument clusters). You will need to find a suitable replacement instrument cluster.

Thank you for the reply. Yes, it's a 1992 model.
Unfortunately, I had actually expected something more positive )))
But what can't be done, can't be done.