An engine control system and an engine control method for improving the ability to start an engine by changing the execution timings of predetermined sumchecks in ROM to shorten the time required for initialization of the system. Upon starting an ECU with a power supply supplied from an AC generator as a result of an operation of a kick starter, a CPU initialization, which includes a hardware reset and a software initialization, is executed. An ignition timing calculation sumcheck, which is required for the calculation of an ignition timing, and injection timing calculation sumcheck, which is required for the calculation of an injection timing, are not executed in a period of the software initialization. Instead, they are executed during BG (background) processing after a movement to routine processing, which upon completion of the software initialization, starts the ECU to permit driving and controlling an igniter and a fuel injector.