bluecitrus

I've done a bit more experimentation, and I've found a method that works for me reliably. I have found it does not matter whether the GPU is powered up or not. Switching it off/on at the wall doesn't seem to matter. Steps would be: 1) Have Macbook Pro powered off, Thunderbolt cable unplugged 2) Turn on Macbook Pro. When the internal display is turned on/it starts booting Windows, plug in the GPU. Ideally before the 'circle' starts on Windows startup 3) See if it works. If not, power off, and try again. Using this method I've achieved about a 50% success rate when starting up. It also means that you can 100% avoid 'black screens' when starting. I have found that you should plug in the GPU after you have already selected Windows, rather than at the boot partition selection screen.

I'd disable automatic repair if I was you. Follow the instructions here. I think it is just about getting the right timing. That being said, I've also never gotten a 'black screen', unless you're referring to getting a blank screen when the Macbook doesn't boot up correctly sometimes.

@tranj10 I'm running Windows off of the SSD of my Macbook. That may be why I get hangs so often: I tried 3 times just now and it wouldn't work. If others have more success of an external drive let me know and I'll switch over. For what it's worth I'm running Optimus too.

Just wanted to say thanks - I'm running an identical setup (although I'm using a Zotac GTX970 rather than an ASUS) and I've got it working. The big problem is the Windows startup: if you don't time it right then Windows will just go into a 'loop' when starting and the circle will keep and keep spinning. I tried using a timer and turning on the Macbook about 10 seconds after I turn on the eGPU seems to work.