Houston, We have a problem.
 
I just hooked up my new 780 Ti to SLI it with my existing card.  They are slightly different but from everything I have read here, they should work well together.
 
Original card = http://www.evga.com/Products/Product.aspx?pn=03G-P4-2884-KR
New card =  http://www.evga.com/Products/Product.aspx?pn=03G-P4-2883-KR
 
 
 
I must have a problem.  I have my new card hooked up and I am getting the same frame rates as I had before in BF4.  This is the only game I currently am playing.
I have tried 2 different SLI bridges.
I have enabled SLI in the NVidia control panel. 
I have reinstalled the driver and restarted.  I only installed the driver 337.50 and Phys X.  It was a clean install.   I had Precision X uninstalled and I said NO to saving profiles.
I have tried each card separately in both slots, both work
I am using the second and third slots since my first slot is not working.
I have maximum performance and single display set in the Control panel. 
I have SLI rendering set at NVidia recommended.
Is there something I have to change in BF4?  I looked but I didn't see a setting for SLI anywhere.
 
I am playing on a Overlord Tempest X270 OC monitor at 118hz on automatic settings as I had before I put in the new card.
My frame rates are in the 60s with some dips into the 50s and some into the 70s.
 
I haven't changed any settings in BF4.
 
Any ideas that you have would be greatly appreciated.
 
EDIT:  I was just playing BF4 and all of a sudden I went into the teens and 20s for frame rates and then my whole rig went blank and froze.  I am now running my original card by itself.  Maybe my new card is bad?  I will test it by itself more thoroughly when I have more time.
EDIT 2:
I am running Windows 7.  I will look at removing the Windows update that was recommended. 
 
I played around with it this morning and I tested both cards and they work fine.  I also tested both slots (second and third) and each of them work as well.  I then tried to SLI again and I was greeted with a blank (dark) screen even though I can hear it boot into Windows.  I took out the SLI bridge and tried to boot up again and I was able to but it looked like it never loaded the driver and was using the generic Windows one.  (like in safe mode)
 
So I then reinstalled the 337.50 driver and it booted into Windows but I still did not have the bridge on.  I think that when I got the blank screen it was because Windows did not load the right driver.  I ran out of time but I think that if I boot into safe mode with the bridge on, I should be able to reinstall the driver at that point and then I can see what then happens.  I will also try playing in full screen mode and see what happens.

 

oh, have you set the refresh rate in the NVidia control panel?  I found that when I installed a new card, the refresh rate on my asus 144hz monitor would default to 60hz

What motherboard?

Randolla

KLEYBA
oh, have you set the refresh rate in the NVidia control panel?  I found that when I installed a new card, the refresh rate on my asus 144hz monitor would default to 60hz

Yes I have re set the refresh rate in the NVidia control panel to 118Hz on automatic timings.
This is what I have been playing at with my original card with no issues.
 
See my Edit to my original post.

Might be that SLI won't work properly without a GPU in the Primary or PCIe slot one. Have you enabled the SLI indicator in the control panel? Have you tried running any 3DMark benches that generally show decent SLI scaling?

NordicJedi

Gomez99
Test the new card with unigine valley 4.0 and 3dmark. Then test with sli and report back scores for us to compare

This^
 
Start there to make sure that you're actually seeing some SLI scaling on benchmarks, or if it's simply running the same.  Yes, it could be a bad card, but all you really need to do is test the two cards one at a time to determine if that's the case.
 
As for BF4, are you running the game in Fullscreen mode or windowed mode?

I am running BF4 in windowed mode. 
I don't have much time today to troubleshoot but I am thinking that the third PCI slot may be going bad. Last night my whole system crashed (Blank screen, no BSOD) I am now running my original card in the second slot like I had been doing all along. I will try it in the third slot and then if that works, Ill try the new card alone and see what happens.  I will test it more thoroughly and report back. 

I have tried the new card in the old slot and it seems to work fine. 
 
I tried the old card in the new (third) slot and it worked as well. 
 
So Unless it is a sporadic thing, I don't think the slot is bad.  Nor do I think the new card is bad.  Could I have two bad bridges?  They are both brand new so I think that is unlikely.  I will reinstall the second card and SLI it and see what happens.  I am not sure when I will have time to run the benchmarks but I will report back my results when I do. 
Thank you all for your help.

Are you running windows 7 or windows 8 or 8.1? If you're running windows 7 make sure windows update KB2670838 is not installed, if it is installed uninstall it then reboot your computer and test.

Randolla
 
I am running BF4 in windowed mode. 
I don't have much time today to troubleshoot but I am thinking that the third PCI slot may be going bad. Last night my whole system crashed (Blank screen, no BSOD) I am now running my original card in the second slot like I had been doing all along. I will try it in the third slot and then if that works, Ill try the new card alone and see what happens.  I will test it more thoroughly and report back. 

In many games, running the screen in windowed mode can seriously hamper FPS and performance.  In some case, like SWTOR, it may disable SLI or CFX entirely (or at least it did when I played last)  When SLI is working again, try it in fullscreen mode to compare fps, if you haven't done that already.
 
Of course, get the card/slot situation squared away first, as testing SLI is going to be impossible if one of those is bad.

I am running Windows 7.  I will look at removing the Windows update that was recommended. 
 
I played around with it this morning and I tested both cards and they work fine.  I also tested both slots (second and third) and each of them work as well.  I then tried to SLI again and I was greeted with a blank (dark) screen even though I can hear it boot into Windows.  I took out the SLI bridge and tried to boot up again and I was able to but it looked like it never loaded the driver and was using the generic Windows one.  (like in safe mode)
 
So I then reinstalled the 337.50 driver and it booted into Windows but I still did not have the bridge on.  I think that when I got the blank screen it was because Windows did not load the right driver.  I ran out of time but I think that if I boot into safe mode with the bridge on, I should be able to reinstall the driver at that point and then I can see what then happens.  I will also try playing in full screen mode and see what happens.

My 780ti's started doing that after I tried the new drivers tomshardware.com had listed and I never could get it worki g back the way it was before the attempted update. I got tired of messing with it and reinstalled windows and all drivers and now im on the road again rockin.

Gomez99
Well before you go and reinstall windows, try the other troubleshooting methods

Oh don't worry about that Gomez.  I don't jut reinstall Windows willy nilly.