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Very low hashrate with RX 580 4GB as second GPU

Hi guys, i am a newbie in mining but after many hours of reading and working now I have fully functional rig RX 580 8Gb at 33 mh/s on ethereum.

But the problem is that I try to use a RX 580 4GB as second gpu but only get 4 mh/s.
I use an old PC with mobo Asrock conroexfire-esata2. I tried the 4GB card in all pciex sockets and also with usb riser on pciex 1x. Also tried the card with similar old mobo and same result but if I use 8GB i get 33 always. If I run mining with only the 4GB card on the mobo I get 20/21 mh/s

I have checked the pciexpress speed using lspci -vv and 5G/s result

I see many people here that gets more than 27 mh/s with RX5x0 cards.

I don´t know what more to do.

Don’t use risers, connect the card directly to PCIE x16 slot.
Mod your card with Polaris bios editor
Use lolminer v1.23 (must)
Overclock it

So yeah, if you have more cards, but only one pciex16, only one can work like that. Others should get around 13. If you have more pcie x16, the performance decreases to like 20mhs from what I tested. Only the first slot is having that much hashrate.

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Hi, thanks for the answer.
Today I bought a RX580 8GB and I have to say that works perfect in the pciex x1 with an USB riser, so i think that my RX580 4GB card is not fully compatible, in fact, hiveos recognize it as RX470/480. I will do some other tests in a different computer.

4GB cards are not ussable for Ethereum mining because of DAG size above 4GB. There is workarround called Zombie mode. Zombie mode use transfer to RAM over PCIe to “replace” missing memory on VGA card. So you can have decent hashrate when 4GB cards are in PCIe 3.0 x16 16 lines only.

My R9 290:
1 x R9 290 PCIe 3.0 x16 25.5MHs
2 x R9 290 2x 3.0 x8 35MHs
1 x R9 290 PCIe 2.0 x16 13 MHs

In that case, how is possible that i have a mobo with pciex 16x and 1x with the same hashrate? 64 mh/s with two rx 580 8gb

Did you read my post?

Yes , I use a zombie mode and still using 4gb cards in other computer and it can mining 24 mhs in pci ex 16x 3.0

I mean that usb riser is not the reason as second post says because 8gb cards works perfectly, one on 16x and one on 1x. But if I use this computer with the 4gb card I have low hashrate.

I dont understand… Is that 4GB card in PCIe 16x with 16 lines or is connecet by riser?

Where i did the first test I have connected to a 16x port and 1x with bad result where I already have 2 RX580 8GB mining 64mhs.

After that, I plugged it in a second mobo in a 16x port with good result, 24 mhs

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