A method for calibrating a solenoid-operated fuel flow control valve assembly for a fuel injector for an internal combustion engine, the injector comprising an engine-driven fuel pump piston in a fuel pumping chamber, a nozzle portion of the injector communicating with the pumping chamber through a fuel delivery passage, the valve assembly including a movable valve spool in the fuel delivery passage, the method comprising the steps of: choosing an initial boot current level for the control valve assembly that will effect displacement of the valve spool to a fuel pressure regulating position intermediate a low fuel pressure position and a maximum fuel pressure position during a fuel injection event; determining whether the chosen initial boot current results in a corresponding boot pressure that will achieve boot injection stability; incrementing or decrementing the initial boot current depending upon whether the initial boot current is too low or too high, respectively, to maintain boot injection stability; changing the initial boot current in successive steps to establish a final upper limit for the boot current above which the boot injection becomes unstable, each successive step being followed by a determination of whether the corresponding boot pressure is too high to maintain injector stability, the boot current that is determined in the final increasing step being delivered to the calibrator controller memory as an upper boot current limit; and changing the initial boot current in successive steps to establish a final lower limit for the boot current below which the boot injection becomes unstable, each successive step being followed by a determination of whether the corresponding boot pressure is too low to maintain injector stability, the boot current that is determined in the final step being delivered to a controller memory as a lower boot current limit. choosing an initial boot current level for the control valve assembly that will effect displacement of the valve spool to a fuel pressure regulating position intermediate a low fuel pressure position and a maximum fuel pressure position during a fuel injection event; determining whether the chosen initial boot current results in a corresponding boot pressure that will achieve boot injection stability; incrementing or decrementing the initial boot current depending upon whether the initial boot current is too low or too high, respectively, to maintain boot injection stability; changing the initial boot current in successive steps to establish a final upper limit for the boot current above which the boot injection becomes unstable, each successive step being followed by a determination of whether the corresponding boot pressure is too high to maintain injector stability, the boot current that is determined in the final increasing step being delivered to the calibrator controller memory as an upper boot current limit; and changing the initial boot current in successive steps to establish a final lower limit for the boot current below which the boot injection becomes unstable, each successive step being followed by a determination of whether the corresponding boot pressure is too low to maintain injector stability, the boot current that is determined in the final step being delivered to a controller memory as a lower boot current limit.