Help with car bc project

For start i'd like to say my english it's not my first language, so i hope you understand.
I have a car, it's a opel astra g 1.7 dti (motor code: y17dt) and i want to make a simple board computer just to show me the instant fuel consumption L/100Km or the mixt consumption.
I have an arduino uno v3 and a 16x2 lcd, and i want to use them for my project.
There are a few projects like mine, but are to show that informations on the car display (TID), i don't want that, i want to show the informations on my 16x2 lcd.
Where do i start ?

Where do i start?

Start with one of the projects like yours and modify the output to display on your LCD.

LCD example can be seen here: