You may not realize how vague your question is, or that no one here knows what you have or how it works. Or even if you want to add software or hardware.

The are many DAC systems available.
Many have PGA inputs to scale the inputs to a match the Your A/D.
Or have scaling so the output reads in the correct units ( I.E. degrees C instead of millivolts)
It is for cars how about a Tach input.
Many Cars use CAN bus you could add that.

Do not over reach unless you expect a better grade for a barley finish big project as compared to a fully complete and documented smaller one.

Do not assume that any group on the internet is full of only people you age. There are people here that are double your age plus. And from all around the world. while they may plow though broken English to help someone. They may not feel the need to decode SMS. You are asking the question, ask in a way that gets You the most help.