Forgive me if this has been asked. I tried searching first.

I have a 8700k and a z370 taichi running the most up to date firmware.

Per the manual I am supposed to put my GTX 1080 in the upper most PCIE (PCIe2) slot near the processor.

If I do this GPUZ reports that the bus is running at "PCIe x16 3.0 @ 1x 3.0" and 3dmark / game framerates are half what they should be.

If it put the card in the middle silver slot (PCIe4) the bus speed reports as "PCIe x16 3.0 @ 8x 3.0" framerates are doubled and 3dmark is much higher (+1000 on Time Spy).

Per the manual a single PCIe card is supposed to go in PCIE2.

The only other PCIE devices I am using are 3x m2 drives total in the MOBO slots.

Am I doing something incorrect, or am I missing a setting?

With the card in the lower slot, graphics are fine and all m2 drives appear to work.

Let me know what other information you may need in debugging this.

Thanks

I thought the z370 chip handles the m2s?

http:// www.overclock.net/forum/6-intel-motherboards/1640221-z370-8700k-m-2-pcie-question-about-pcie-lanes-sharing.html 

Also why would slot 2 run at 1x? But slot 2 runs correctly at 8x.

If that doesn't work RMA it.

I think the 4 lanes between the chipset and the processor are dedicated... I mean assumptions here.. but they have to be. Otherwise ANYONE using a single m2 drive would lose x16 on the main PCIe gfx port.

It still would not explain why the card gets x8 from the lower x8 slot. If it were sucking 4 lanes from the 16 to run the chipset the top slot would run at x8.

I reseated the processor / cpu cooler / checked for any damage to the CPU / mobo. No bent pins, no marks on the CPU dots.

It all looks fine.

Re-seated, put card in slot 2 its x1.

Does anyone know if there is something in bios that can control this?

I have already cleared CMOS and reset up my settings, changed nothing.

I see from reading other issues Asus mobos show you the lanes in bios for each slot. The bios for the Taichi does not have any section related to this.

The only setting I see is the PCIe slot link speed. Which I have tried auto and gen3 on slot2. Slot 4 is on auto and works at x8.

I am thinking there is either something inherently wrong with the controller in this processor (doubtful?) or this mobo needs an RMA.

Any other ideas?

Thanks.

I have done every recommended option for fixing this from the graphics config side. Putting the card in slot 4 immediately reports x8 regardless of whether the card is under load. Slot 2 reports x1 no matter what.

You can see my back and forth on EVGA forums here: https ://forums.evga.com/1080-SC-Performance-m2806455.aspx

I also tried removing all but one m2 drive, still x1.

I saw a post on another forum just recently with this same issue and it turned out that the GPU was sagging and it was causing poor contact along the top edge of the GPU nearest the front of the case. PCIe slots are set up by length for the different lane configs, 1x is the first small section nearest the rear of the case, x2 a little closer to the front of the case and so on till you get to x16 which is the last third or so of the slot. The device will work even if only the x1 portion is making contact. This leads many to believe the card is properly seated and to dismiss the slot fit as a potential source for the issue.

Try supporting the GPU on a small box or some such that keeps it exactly level or very, very slightly tilted up at the end. See if that gives you your full x16.

I am not sure exactly why but x8 wired slots tend to be a more snug fit for some reason, possibly due to fewer traces and less applied heat at the end of the slot during manufacture. 

Let us know if this helps.

He already got it fixed with RMA. It was a bad motherboard.