Well, I have a turbo diesel myself, never had that kind of problem.

I bought it one year ago, pending is alignment and injector callibration.

My car is yealding about 25 mpg in combined use, but I never attempt to make a calculation with a few liters. You must to that for a whole tank of fuel.
The car has 250k of use.

Besides that, yr tank must breath, your air filter must breath, yr fuel filter must be kept in condition, and you should make an injector callibration and cleaning. As to have a secure base to begin getting normal fuel economy.

Oldbeaver