Diagnostic system and method to temporarily adjust fuel quantity delivered to a fuel injected engine

The present invention provides a system and method to adjust temporarily the quantity of fuel delivered to the cylinders of a fuel injected engine. The present invention allows a service technician to temporarily adjust the quantity of fuel being delivered to each cylinder or all cylinders of an internal combustion engine. The system includes an internal combustion engine having therein an electronic control unit capable of controlling the fuel quantity delivered to each cylinder and a general service computer connectable thereto and capable of transmitting data to the ECU. When instructed by the service technician, the service computer sends signals to the ECU to adjust fuel injector data to the fuel injectors of so as to increase or decrease the amount of fuel being delivered to the fuel injected engine.