Originally Posted by dyfk3l
Extract the kernel.sin from your FTF-file and flash this immediately after installiung SuperSU (as mentioned: not reboot, rather remove battery!) via flashtool => fastboot.
edit: Extracting works with WinRar e.g.
1 I go to fastboot mode and with flashtool flash kernel.elf NK for Xperia V 1.4.0
2 Reboot to recovery and flash Supersu
3 Turn off device and reboot to fastboot mode and flash kernel.sin from original ftf