Update to my Firmware Problem. Erase USB choose GUID partition map with journaled, I still had the same problem with Firmware update, when tried to install onto USB. I did finally solve it combining some of your ideas. I used website http://dosdude1.com/highsierra/. I downloaded his tool (macOS High Sierra Patcher) onto another mac created the USB you mentioned in previous post. Following steps 1-3 on the other Mac. Step 4 I started in the Mac with the firmware update problem. I followed steps 5, 6, 7. completed the High Sierra install with the SSD drive (OWC Accelsior S + 1.0TB Extreme Pro 6G Solid-State Drive Bundle.) . I did not do the other steps listed. Instead I ejected the USB drive that I used for the install, rebooted the Mac several times to make sure the Mac started as expected. All was great. I was still not sure if I fixed the problem. So I installed a spare drive I had into the Mac drive bay. Restarted Mac. the new drive was recognized. I used Disk utility to erase and format drive. I downloaded High Sierra from the app store. I shut down the Mac. I restarted the Mac holding down the Command key and the R key, until apple logo appeared. The Menu came up where you select the four different options. I used disk utility again, and both drives were recognized, so I exited back to Menu with 4 options, click on the Install, and up came the install firmware update message.!! I clicked on button, and another box opened wanting the administrator pw, I entered, and system shut down as the screen message stated after a short time. (I was holding my breath) The screen message had stated to restart, hold power button till light flashes or hear long tone. I held the Power button, just as the light flashed the long tone came on, the apple logo appeared, after a time the Mac shut down, and started back up, and came up normal. I started and shut down the Mac a couple more times. everything was working normally. I tried to do the install again, with push power button and hold command key and r key until apple logo appeared. Menu with four options came up, I selected disk utility, both drives were still recognized, so I exited that menu. Now the main menu up again, selected install and no more firmware update menu. I am now happy to work with the Mac. I even had chatted Mac support, and they had me try many other procedures, to now avail. Now I have a fast mac with the SSD drive. Several days just to install new drive. I may be tempted to go with Microsoft next time.
