What do you mean by track vehicle? Do you mean where currently are they?

Also what do you mean by diesel usage? Do you mean you want to enter litter/gallon somehow along with the cost for gas bills?

Dear @aaghaei Yes I mean where currently are they ? 
and cost and litres of gas bills

If your vehicles have internet connection you can create an account for driver in Acumatica and enable location tracking so you will be able to see the last location. You can set frequency of update and also distance change to track.

Regarding the gas, you can setup your vehicles as Subaccount and when you enter gas bill in AP, then in quantity enter the litter/gallon and in the amount the bill cost. In account you will choose your Fuel GL account and in Subaccount your vehicle. Later you can run report on each vehicle gas usage and cost if you enter all data correctly 

with above logic you can track your vehicle leases, maintenance, insurance… as well in addition to fuel.