How can I improve the efficiency of my Ford Transit Custom engine?

I've been having trouble with my Ford Transit Custom's engine, it seems to be using more fuel than usual and it's not performing as well as it used to. I'm not sure what the issue could be, but I'm looking for some advice on how to improve its efficiency.

One possible cause of your engine's decreased efficiency could be a clogged air filter. Have you checked and replaced your air filter recently? This is an easy fix that could significantly improve your engine's performance.

Another common issue with Ford Transit Custom engines is dirty fuel injectors. These can get clogged over time and cause decrease in efficiency. I suggest using a fuel injector cleaning solution to see if that helps.