An engine includes a plurality of combustion cylinders configured to burn a fuel to power the engine, and a plurality of fuel injectors. Each of the fuel injectors is arranged to distribute fuel delivered from a fuel tank to one of the plurality of combustion cylinders. The engine also includes a controller programmed to adjust a fuel trim signal gain based on sensing exhaust flow downstream of the combustion cylinders. The controller is also programmed to monitor a cumulative misfire count for each of the plurality of combustion cylinders. The controller is further programmed to issue a prognosis message identifying a state of health of at least one of the plurality of fuel injectors in response to a fuel trim signal gain exceeding an adjustment threshold and a cumulative misfire count greater than a misfire threshold.