Upgrade mac pro 4.1 to 5.1 does not work (it just reboot normally) In my quest to update my mac pro 2009 (4.1), I did encounter a roadblock, since the last OS that I can run on 4.1 is 10.11. 

Now; I found a method to flash the machine so it becomes a 5.1; which allow me to install up to Mojave I believe. The problem is that after following the instructions, the machine won't update. This is what I did


mount the firmware update DMG and run the app, it create a ram disk on desktop
Once done, it ask me to shut down the computer and restart it.
I restart as per instructions; holding the button until the light flash and the machine beep, but it just boot in the current os, and no update is done


I did check the following


my 4.1 mac has the latest firmware available officially from Apple
I have the original GT120 that came with it, in the bottom slot (not the 16x, since that card is garbage); also the only other devices plugged in, beside the mouse and keyboard are 2 extra hard drives.


So far, after reading forums and tons of huge posts, I found no way to solve my problem. So I hope anyone here has experience with the procedure and can point me to the right solution. Once I get this done, my second step will be to go for High sierra or  Mojave, and then try to install windows via bootcamp, but one step at time.
First, check the requirements:


64bit EFI needed (MacPro 4,1 has it)
latest firmware Update (You seem to have this)
Do you have enough memory and CPU? (I upgraded my MacPro to 32GB RAM and 2x QuadCore 3.2GHz CPU.)
Metal capable GPU like newer nvidia 960/980/1080 GTX?


I am running Sierra 10.12.6 fine on my MacPro 3,1 with latest 1.5 firmware, but I used the installer coming from http://dosdude1.com/software.html, which creates a bootable USB media to install from. That worked like a charm.

So I suggest you try the software from dosdude1 - there is a perfect instruction page how to build the installer from the original Apple Installer and how to use it. (Never ever forget to apply the patches regarding software update provided by the dosdude1 installer!)

I already tried to upgrade to High Sierra and got the feedback from Collin aka dosdude1 that I would need a metal capable GPU, because I got several weird hang ups with my ATI R9 280X during the installation process. Therefore I need to buy a new Nvidia GPU, preferably a 980GTX.