Replacement motor for transit 2,5D ’94

Hello together, I recently got a motorhome on Ford Transit basis with 2.5D engine with 74KW from 1994. When buying (from private) I was told a consumption of 10-11 liters, but after our Sweden vacation the astonishment was great. The cut-through at about 4000 km was 16 L / 100 km! Since the Womo also has no environmental badge and also does not get got me the idea that maybe a newer engine could solve the problems consumption and plaque. Therefore I would like to ask you if it grun In addition, it is possible to install a newer date engine with better consumption values in transit ’94? Thank you very much and best regards Tom