Rampage IV Extreme and 8x8gb G Skill at 2400 not stable

[Sadvocate]

Howdy folks,

Thanks for looking - here's the skinny:

Can't get 8 sticks to pass prime 95 at 2400, although each stick has passed prime 95 stable for 24+ hours (ran 4 for 24 hours then ran the other 4, all pass). I ran them 24 hours on Memtest, then 24 hours prime 95 - works fine with 4 sticks but not all 8 (8 passes Memtest, but not Prime 95).

Rampage IV Extreme (3301 Bios)
3960x CPU (set to Auto multiplier)
8x8gb kit of G Skill F3-19200CL10Q2-64GBZHD (supposed to run at 2400)
2x680GTX in SLI
2xOCZ Vector SATAIII in Raid 0
3xWD Red Sata II in Raid 5

Using XMP profile 1 (and Mode 1 inside DRAM timings per G Skill's website recommendation), configured with LLC to medium, 180%, the memory is all at extreme, 140% per Raja's guide - but no overclocking yet - just want to pass Prime95 at stock speeds and DDR-2400 with all 8 sticks.

As far as voltages, everything was set to auto except VCCSA, which was set to 1.25 per the XMP profile. The VTT was up at 1.35 and the Vcore at 1.36 at full load (again, these are auto set, those are just the readings).

I can't get it to pass 24 hours of Prime95. I've tested 4 of the sticks at a time and the system is prime95 stable at 24+ hours, so I know the RAM is good.

With all 8 sticks in at 2400, I left Memtest running over the weekend and it made it through 6 complete passes (57 hours) with no errors, but Prime95 fails after about 3 hours. I've upped the VCore incrementally to 1.45 and saw no improvement - first core fails within 2 to 3 hours, and another core about 3 hours after that. I've had VTT as low as 1.1 and as high as 1.4 and it also appears to have no effect on Prime95 stability.

The memory is supposed to run at 2400 - the processor has no problem handling 4 sticks of it, and for at least a few hours all 8. I also know all 8 sticks are good.

I'm stumped. Any help is appreciated.

Cheers!

[HalloweenWeed]

Did you plug in EZ_PLUG_2?

[SUKARA@ASUS]

Memory run 2400Mhz is oc mode,provide the link by G.skill for you reference
maybe you can detail check about this...
https://docs.google.com/document/pub...0OU5VPe6CUoFso

[Sadvocate]

Did you plug in EZ_PLUG_2?

Thanks for replying - yes, I've got the EZ_PLUG_2 plugged in.

[Sadvocate]

Memory run 2400Mhz is oc mode,provide the link by G.skill for you reference
maybe you can detail check about this...
https://docs.google.com/document/pub...0OU5VPe6CUoFso

Sukara, thanks for replying - I have seen this document and configured my system accordingly; this is how I ran Memtest for 57 hours stable with all 8 sticks in, which leads me to conclude the RAM is not the issue.

[HalloweenWeed]

Sadvocate, I know you think that just bc your RAM says it will run at 2400 that you should be able to do that, and that is just not the case. It depends on your CPU IMC. Read the first two paragraphs in Arne's sticky at the beginning of this forum:

Rampage IV Extreme RAM Guide

That said, there could possibly be a way to run it that fast, you should be patient and wait for another answer. In the meantime, plz try lower speeds.

[HiVizMan]

Please confirm that you ran memtest86+ for 57 hours at the XMP profile speed of 2400MHz. And not at stock.

[Sadvocate]

Please confirm that you ran memtest86+ for 57 hours at the XMP profile speed of 2400MHz. And not at stock.

Yes, I ran Memtest86+ for 57 hours at XMP Profile 1 and speed 2400 - I also tested half of the sticks (4 at a time) at the same settings and both halves passed 24+ hours of Memtest and Prime95. It's only when I try to run all 8 at the same time that it fails during Prime95, even though it passed Memtest.

Thanks for your help.

[HiVizMan]

The fact that all 8 sticks pass memtest86+ and fail prime indicate that it is not your memory that is preventing you from passing Prime. Does your system pass prime with your CPU at default/stock with all 8 sticks fitted.

[Sadvocate]

Sadvocate, I know you think that just bc your RAM says it will run at 2400 that you should be able to do that, and that is just not the case. It depends on your CPU IMC. Read the first two paragraphs in Arne's sticky at the beginning of this forum:

Rampage IV Extreme RAM Guide

That said, there could possibly be a way to run it that fast, you should be patient and wait for another answer. In the meantime, plz try lower speeds.

If it didn't pass Memtest I'd be more inclined to believe the crash during Prime95 is related to the limitations of the IMC controlling the RAM at that speed, but it doesn't. I'll try lowering the speed and see what happens.

Edit: Thanks for the link - not sure how I missed reading that, but I'm doing so now.