Apprentice:

One of the most common reasons for excessive fuel use is carbon build up in the engine, particularly in the intake system.

Are there any other ways to stop that from happened or fix it? 

Allan: 

Carbon build up gives the wrong signal to the ECU and tends to upset air fuel mixture readings. Apart from cleaning it out, which is expensive but of course only the ultimate way to fix it, I personally like to use the vehicle harder for longer runs (at least two 1 hour runs a week). I think you should use a common rail diesel fuel conditioner of some sort to keep the injectors clean and you don't get the carbon build up. 

Apprentice:

One of the most common reasons for excessive fuel use is carbon build up in the engine, particularly in the intake system.

Are there any other ways to stop that from happened or fix it? 

Allan: 

Carbon build up gives the wrong signal to the ECU and tends to upset air fuel mixture readings. Apart from cleaning it out, which is expensive but of course only the ultimate way to fix it, I personally like to use the vehicle harder for longer runs (at least two 1 hour runs a week). I think you should use a common rail diesel fuel conditioner of some sort to keep the injectors clean and you don't get the carbon build up.