Missing PCIE lanes? PCIE x16 only runs at x8, and PCIE x8 only runs at x1

[Rog442]

Hello community,

I never really post on forums, but I'm unable to find someone with this exact problem who found the solution...

I've noticed a problem with my PCIE slots. My motherboard has 2 PCIE x16 slots. Up to now I've been using only one video card, so I never noticed anything peculiar. However I purchased a second video card, and now I cannot Crossfire them because when both cards are plugged in, it goes to a x8/x1 configuration, instead of x8/x8 as advertised. Similarly, if only one card is in slot 1, it functions at x8 (instead of x16), and if only 1 card is in slot 2, it functions at x1 as well (instead of x8). This is true not only at idle, but under stress as well.

Basically, my motherboard specs show :

PCIE x16_1 Single card = x16
PCIE x16_1 Dual Card = x8
PCIE x16_2 Dual Card = x8

And this is what I'm actually getting :

PCIE x16_1 Single card = x8
PCIE x16_1 Dual Card = x8
PCIE x16_2 Dual Card = x1

These are the measures I've tried :

- Tried each card in different slots, together and one at a time
- Taken out and reseated them multiple times
- Took off my CPU waterblock to make sure the backplate wasn't touching anything, and the CPU itself and the socket look fine
- Tried deactivating anything that looked like it had to do with power savings in Windows and BIOS
- Tried with and without Crossfire link
- Flashed BIOS, now at latest version
- Installed latest chipset and firmware drivers
- Completely erased and reinstalled ATI Catalyst software and drivers

Here are my specs :

Asus P8Z77-V LK motherboard
i5-3570k CPU (not overclocked)
Sapphire HD 7870 Ghz Edition graphics card
Gigabyte HD 7870 Ghz Edition graphics card
Corsair TX650 psu
1x 8gb Corsair Vengeance DDR3 ram

I'm reaching out to you guys 'cause I'm in a real pickle! Please let me know if you require any additional information.

THANK YOU

 

[TheGuruStud]

It shouldn't matter for a board without tons of slots, but is there anything in the bios?

 

[OneMoar]

board only supports 3.0 8x+4x or 8x8 when running crossfire AND a pcie 2.0 card
right here in black and white http://www.asus.com/us/Motherboards/P8Z77V_LK/specifications/
there is nothing wrong here
PCIe 3.0 x4 is equal to pcie 2.0 x8
just to be sure you are using the blue and white slot correct ?
don't use the black slot

 

[Rog442]

Hi,

@Gurustud: BIOS only displays that it's running x8/x1, but can't be changed.

@OneMoar: Yes, I'm using the blue and white slots only. No other pci slot is being used. And the specs do show "2 x PCIe 3.0/2.0 x16 (x16 or dual x8)". The dual x8 is what I need to happen, but it's only giving me x8/x1, therefore I can't use Crossfire. I can't wrap my head around this one... And also bizarrely with only one card it still runs x8 instead of x16.

Thank you

 

[OneMoar]

Hi,

@Gurustud: BIOS only displays that it's running x8/x1, but can't be changed.

@OneMoar: Yes, I'm using the blue and white slots only. No other pci slot is being used. And the specs do show "2 x PCIe 3.0/2.0 x16 (x16 or dual x8)". The dual x8 is what I need to happen, but it's only giving me x8/x1, therefore I can't use Crossfire. I can't wrap my head around this one... And also bizarrely with only one card it still runs x8 instead of x16.

Thank you

are you running the gpu-z render test when you are looking at the peg speeds they decrease when there is no load on them regardless of the PCi-E power saving setting

 

[Rog442]

Yes correct, even when running the gpu-z render test only the gen will change, i.e. can vary between 1.1, 2.0 and 3.0, but no change on the number of lanes.

Thanks

 

[wagana]

Are you using a wi-fi/sound/whatever card in one of those x16 slots?

 

[Rog442]

No, no other slot is being used, only two graphics cards in the two PCIe x16 slots.

Is it possible my mobo or CPU are just broken I wonder?

Thanks

 

[OneMoar]

No, no other slot is being used, only two graphics cards in the two PCIe x16 slots.

Is it possible my mobo or CPU are just broken I wonder?

Thanks

more then likely its the cards at fault here one of them isn't playing nice and not negotiating the speed correctly
poke the around the bios and see if it has a PCI gen setting force it to 2.0 for the affected slots

 

[Rog442]

Yes that could be a possibility, but it would have to be both cards, because even when I try each card in each slot individually, slot 1 always gives x8, and slot 2 always gives x1.


Here's how it looks in bios :

Changed to Gen 2 under stress :

I don't know if anything else looks weird there. If not, I'll try to find a different cpu to test it on, and maybe a different video card.

Thanks

 

[OneMoar]

take it off auto ?
set it to 8x 2.0 and x8 2.0
?????
if it won't let you change it pull one of the cards and change it and re-install and check it again

 

[Rog442]

That field that says "auto" is just to select Gen 1, 2 or 3, or auto. I can never change the x8/x1, even if just one card is installed.

Thanks

 

[OneMoar]

whats gpu-z report if you force Gen2 ?

 

[Rog442]

Here are both cards at Gen 2 under stress. I guess the second one stays throttled at 1.1. :

Thanks

 

[newtekie1]

What CPU cooler are you using? It may be over tightened and causing the CPU to not make proper contact with the socket.

 

[OneMoar]

try mixing the gen modes set PCIe_2 to gen3 and PCiE_1 to GEN2
or 3.0 and 1.1 or 2.0 and 1.1
ect ect ect

 

[OneMoar]

What CPU cooler are you using? It may be over tightened and causing the CPU to not make proper contact with the socket.

he said he already re-seated his block I guess he could try backing the screws off a turn
its possible but extremely extremely unlikely that the CPU is to blame
Could also be the PLX chip on the motherboard is toast either way its acting like there is insufficient PEG-LANES available
which could be anything from a bad card to a damaged trace or the cpu being to tight or just borked

 

[Rog442]

I had already loosened my cpu waterblock. Now I loosened it quite a bit more, and also loosened the screws on my motherboard a bit, and still no change. And also tried mixing gen modes as well. The only thing left to do is to troubleshoot each piece of hardware. If it is the CPU or motherboard that are broken, I guess I'll just go back to one card at x8 until I'm ready for an upgrade sometime.

Thank you for your help. I will report back if I'm able to find anything conclusive.

 

[OneMoar]

honestly multi-gpu setups are always more trouble then they are worth in my book

 

[newtekie1]

Since it is reading x8 and x1 in the BIOS you can be sure it isn't a software issue. It also isn't a power saving feature as the BIOS reports the maximum link speed possible, ignoring any power saving options. Also, you shouldn't have to force any settings for this to work, it should just pick up both as x8 in the BIOS.

Could also be the PLX chip on the motherboard is toast either way its acting like there is insufficient PEG-LANES available

The board doesn't have a PLX chip. But I am starting to think there is a hardware issue with the board causing this.