Mac Pro 4.1 (flashed) High Sierra Firmware Update

I just created a USB Installer for High Sierra and tried to install my Mac Pro 4.1 (flashed to 5.1).

But the installer wants to do a Firmware Update too and says I have to shutdown and press the power button until the EFI beeps. But this Shutdown button in the installer is greyed out so I can't proceed.

Any help?

Okay, I got it.

First, I installed Sierra an a USB drive and did all updates.

Then I inserted the High Sierra USB drive and started the installer. And voila, I was able to press the shutdown button and did the EFI update!

I found this on MacRumors...

Yeah you get a firmware update! :eek: first time the 5,1 has gotten a firmware update in ages! I did not get it when updating from DP1 to DP5 but if you make a DP5 installer, it says you must update your boot rom before you can install and it tells you how, the shut down button did not work for me but going to the apple menu and hitting shut down worked for me :) then i followed the normal hold power button until flashing power light and bam it did the firmware update! and im using a flashed 4,1 to 5,1 Mac Pro! so yeah looks like flashed 4,1s are so identicial they happily take the High sierra boot rom update! :D

So it looks like you'll be OK if you:

1. Click the shut down button which lets the installer write the firmware to disk.
2. Go to the installer menu and click "Shut down".
3. After the machine shuts down, hold down the power button for 15+ seconds until you hear a beep. The power light will flash quickly a few times before it beeps
4. Release the power button and allow the firmware update to proceed. DO NOT shut down the machine during the firmware update.

Reading further down that thread -

Just a heads up to update the firmware on a Mac Pro 4,1 or 5,1 you have to install an EFI video card (this is true also if your flashing a 4,1 to a 5,1) if you dont have a EFI video card then it won't update

Note: I gave up after about 6 pages of that thread, but the general consensus seems to be the above instructions do work.

Let us know how it goes - I have a similar machine...

Update April 2018
I just attempted this myself [eventually]. I first stripped all except the boot drive [Samsung SSD in the optical bay] & keyboard/mouse. Successfully got the Restart button to work, no probs, but the firmware update didn't succeed after holding the button until the light flashed.
After a bit of Googling, I found a note that said to hold the button not only until the light flashes, but keep holding until you hear the beep tone. After doing that, it worked & all went smoothly after that. The OS update is actually a separate process, which I hadn't realised until that point.