I just did mine. you need 2 computers (both mac's is easiest!)
I have a mid 2014.
Unplug the battery.
Unplug power.
Connect your SOIC 8 pin clip to the chip MX25L6406E (to the right of the battery connector)
Pin 1 goes to the dot.
plug the other end into your CH341 adaptor
note that pin 1 goes the other way in the CH341a adaptor.
(see the red pin in the middle, as its a 25xx chip)
View attachment 833042
use flashrom and dump the rom.
use homebrew (brew.sh) and
brew install flashrom ..
may need to fiddle with the soic adaptor positioning.
My chip was a MX25L6406E, so i dumped repeatedly for safety
eg
flashrom -p ch341a_spi -r rom.bin -c "MX25L6406E/MX25L6408E"
flashrom -p ch341a_spi -r rom1.bin -c "MX25L6406E/MX25L6408E"
flashrom -p ch341a_spi -r rom2.bin -c "MX25L6406E/MX25L6408E"
suggest read / dump 2-3 times, then diff between the dumps so you can confirm a good dump.
then
diff rom.bin rom1.bin
diff rom2.bin rom.bin
or md5 *.bin
should be identical, if not, then DON'T PROCEED, check cabling and retry till you have good dumps..
Next get the uefitool from here -
https://github.com/LongSoft/UEFITool/releases/
You'll need to use the non Axx version, eg 0.26.0 (currently), as that allows writing.
Grab the 2015 efi from here -
https://github.com/gdbinit/firmware_vault/tree/master/EFI/MacBookPro
( MBP114_0183_B00.fd )
use UEFItool and open the fd version, and open a new window and open your dump
in the fd file, search for guid 5111 (APPLE F to search), select it in the search results to open the guid
then right click the guid and export to ffs file.
in the dump search for guid 5111 (apple f to search), select it in the search to open the guid
right click the guid and import the ffs file.
save your rom as modified.rom
reflash with flashrom.
eg flashrom -p ch341a_spi -w modified.rom -c "MX25L6406E/MX25L6408E"
unplug, and test.
If you go wrong, you can always revert the saved rom file and try again.
The instructions at the beginning have more details.
Good luck!