car avagrage

[nikonjems]

hi

guys i am new to this forum. i Need your help.

I have one car which i buy 4 year before. Running quite good. but now from last 1 month my car showing some fuel problem. When put 4 or 5 litter Desel the car is giving that much of avarage which before runs. i'm not getting it how directly reduce this much of avagrage in one month.

Please guys help me is anything i do in my car.

Thanks