Update 4.90 details here:
https://www.psx-place.com/threads/exploiting-4-90-ps3-firmware-installing-cfw-running-ps3hen-cfw-flash-writer-is-back-in-4-90.39772/ , Things have change a bit in 4.90 guide will need updated to reflect changes
Guide Updated by @Coro
Hacking A PS3 by Coro
USING THIS...