Make sure you check your motherboard manual, you will find there which slot uses how many lanes and how to get up to 16.
If it was a sudden drop in fps performance, it wasnt in the wrong slot. Probably the card wasnt properly seated and some bump in the pc messed this. He only need to turn off the pc take out the graphic card and put it again edit: and turn on again
I removed and firmly re-attached the GPU in 16x Slot and it keeps showing x4 in GPU-Z. So it seems to be a dead end.
It depends of your hardware. For pcie 2.0, gtx 780, ssd, 16 go ram ddr3, i5 2500k, I hardly had any improvements. Now I have a powerful PC, but RF2 is the only simulation where in ultra/full hd I sometimes go below 60 FPS. It's not normal for this resolution, with a GTX 1080, all other simulations work perfectly. And I did not say that the performance update did not work, I just said that it was not at all up to the stakes.
Try again. Not too much force. If worked before will work again edit: in my case, sometimes i got x8, x4... about 3 attempts until got it right. I think the slot was already messed up. It could be your case too
Did you actually switch the slots? I believe most motherboards have the faster x16 slot right next to the CPU, the x4 slot is usually the lower one. The x16 slot should never work at x4 under normal circumstances, x4 is a bottleneck even for other games than rF2.
Is your gpu in the first slot on the motherboard, ie the the first one underneath your cpu. There are things that can take up the bandwidth on that slot, and make it run x4, I can’t remember though what they are as I’m drunk. What other things do you have plugged into your pcie slots, and what hard drives do you have
Did you check your motherboard manual? It will tell you there when the PCI lanes are shared with other devices. Any reason why you don't share your system specs (motherboard, devices installed, etc)? You will get better help if you do. It is kinda pointless for everyone else here to guess what might be your problem when you can just give the requested info.
Don't blindly trust GPU-Z, it sometimes shows improper information, better trust the mother board manual.
@ECAR_Tracks As you can see PCIe is 3.0@ x16 1.1 Click ?, Start Render Test and PCIe should be 3.0@16 3.0
The current hardware is (was) Maximus VII Formula (Mobo) + 16 Gb Ripshark RAM = i74790@4.4 Ghz In fact I couldn't make it work x16 in any circumstances. Tried everything it kept informing me [x16 maximum capacity][x4 current speed]. The render test suggested by @Ari Antero does nothing, it keeps at 4x no matter what. Took the Graphics Card off and replaced a number of times, same result. Put in other slots, no boot at all, so it seems to be something damaged (CPU pins, PCI-e Slot itself, who knows). Got tired to keep playing with this and went for a brute-force solution: Let's see if the things get sorted now.