Its basically a Check Engine Light, or Service Engine Soon, however you want to look at it, basically you have some kind of code the ECU has discovered and now its dispaying the alert to the operator.
The most likely causes for the FI light are removal of your exhuast servo, if you took off your exhaust and removed the exhuast valve and completely removed the actuator servo, you should hook the servo back up and just remove the cables. (this is the most common FI light issues, there are many other see a service manual)