All gasoline sold in the United States is required to contain effective detergent additives. Use of additional detergents or other additives is not needed under normal conditions and would result in additional cost. Therefore you should not have to add anything to the fuel.
See also:
Fuel consumption
The fuel consumption figures given in the table below are determined on the basis
of the homologation tests set down by specific European Directives.
The procedures below are followed for measuring ...
CO2 emission at exhaust
The CO2 emission levels at the exhaust given in the following table refer to
combined consumption.
...
Installation of electric/electronic devices
Electric/electronic devices installed after buying the car or in aftermarket
shall bear the and marking:
Fiat Auto S.p.A. authorizes the installation of transceivers provided that installation
...