A method of controlling an engine includes the steps of: applying a current to the electromagnetic coil to move the at least one piston from the fully retracted position toward the full stroke position; sending a signal to an electronic control unit (ECU) when the at least one piston reaches the full stroke position; determining a time taken to reach the full stroke position from the fully retracted position based on the signal; determining a power-on time based on the determined time taken to reach the full stroke position from the fully retracted position; and returning the at least one piston to the fully retracted position by stopping to apply the current to the electromagnetic coil once the power-on time has elapsed.