RomRaider

hi i was wondering if i can safely flash an 04 sti rom to an 06 sti ecu and will by-pass immobilizer, dont want to buy another ecu

Somebody has done this for MY05 Legacy and wrote MY04 ROM without immo.
But.
Be ready to recover the ecu in SHbootmode if something went wrong.

Which ROM's are you trying to do this with and what market? USDM or EDM etc

The issue will be with 06 STi being DBW

USDM will not work, 04 is a sh7055 512kb rom, the 06 is a sh7058 1024kb rom.

In other markets, it looks like most 04's were 16bit, and 06 are mostly 32bit.

Only attempt it if the file sizes match, and have shboot cable ready.

This is not a problem provided primary bootloader is rewriten as well (FHI firmware could not do this).
Hardware registers and ROM partitions are upward compatible for those chips. Internal reflash algo\registers are probably not. That means that FHI firmware will probably fail to update reflashed 7055 code.

The thing is, the OP wants to bypass the immobiliser. The immobiliser circuit is not in that part of the ROM.

thanks for all the info, turns out my mechanic plug the immobilizer in the keyless entry plug instead of the immobilizer plug. but everything is up and running now

thanks