GTX 1080 TI only works in the first PCI-E slot, not the second

[Aleppi]

So I have been using my GTX 1080 TI in the first slot of my Asus Z87 Pro motherboard for a while without issues, but I bought a RX 5500 XT for Hackintosh. But to use the AMD card for Hackintosh, I need it to be in the first PCI-E slot. Putting the AMD card in the first slot and the 1080 TI in the second slot works, but the BIOS doesn't detect a card in the second slot. Putting the GTX 1080 TI in the first slot and the AMD card in the second slot, both cards are detected and are running at 8x. So my AMD card works in both slots, which means that the second PCI-E slot is working, but my GTX 1080 TI only works in the first slot, which means that the 1080 Ti is working. But I cannot seem to get the 1080 TI working in the second slot.

 

Does anyone have any suggestions on how to fix this?

[Korben]

deleted. read wrong.

[Tristerin]

Uninstall all drivers on the system (DDU software, in safe mode as it will direct you too) then download the drivers fresh with this setup you intend to have.  At least that's what I would do if I had an issue with a second card I knew that worked.

[Tristerin]

Just now, Korben said:

Take a look in your manual

That means with a single card using x16 it will have no PCIe lanes for the second slot.

 

If you share the slots PCIe bandwidth they can both operate at x8 x8.  Remember he is seeing the cards when mounted in reverse (AMD card on bottom, NVIDIA on top, both at x8)

[Korben]

Just now, Tristerin said:

That means with a single card using x16 it will have no PCIe lanes for the second slot.

 

If you share the slots PCIe bandwidth they can both operate at x8 x8.  Remember he is seeing the cards when mounted in reverse (AMD card on bottom, NVIDIA on top, both at x8)

Yeah I know. I have to learn to read before posting. Sorry.

[Tristerin]

4 minutes ago, Korben said:

Yeah I know. I have to learn to read before posting. Sorry.

No worries!  Just didn't want OP spending time on that

[Korben]

After really reading your post (:)): maybe, this just me guessing, the second slot has not enough power for a 1080Ti. Z87 is a long time ago for me, but I think there was kind of an issue/note with PCI Power on some boards. Also, and that totally a guess, the 2nd slot shares interrupts with some SATA ports and another PCI Slot. Maybe the 1080 is pickier with this than AMD? I would try to remove any device from the SATA ports (the Asmedia/brown ones) and the PCI slot (3rd one). Then check BIOS. Just to be sure.

[Vishera]

One of the slots on the board is PCI-E 2.0 x16 in x4 mode,

Nvidia cards outright refuse to work on 4 lanes,you need at least 8 lanes for an Nvidia card to work.

Luckily you have another slot which will operate at PCI-E 3.0 x8 if the top slot is populated.

[Aleppi]

So I tried to uninstall all my drivers using DDU uninstaller, but since it was the motherboard not detecting the GPU, not Windows, nothing changed as I thought. The only populated PCI-E slot other than the GPUs is a network card in the uppermost 1x slot, so my guess is just that the 1080 TI thinks it gets too little power from the second 8x slot while the RX5500 XT doesn't seem to complain. Might try more later, but for the moment I am giving up on this, will probably have to wait until I get a new motherboard and CPU.