I also have this underperforming problem with an S4.
Although the "Mining Status" shows 2000+GH/s I only get ~100GH/s @ghash.io and about 200GH/s at eligius.st.
I am using a 10A power cord since we have 220V here (1400W / 220V = ~6,4A) and do not expect that this is the problem.

I would recommend any suggestions on the performance, thanks.

Hello I have 2 S4's and prefer to use Eligius, but I'm also having tons of trouble with that combo.  I don't have any solutions, but wanted to provide data from my equipment for confirmation of the problem.
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Below is a link to 2 screenshots of the S4s running on Eligius vs Eclipse.  Note the accepted shares and "Effective Hashrate"

http://1drv.ms/1E6MPRV

I too am seeing nowhere near the advertised hash rate poolside, even though the web ui is reporting close to 2100 average.  I am seeing about 1.67 TH poolside average after several hours.

My antminer s4 is also not working on eligius or ghash, but it's reporting in its own control panel that it's mining at 2000+ gh/s. What is the deal?

I did a buy on the S4's and their hashrate locally is 2th/s or greater (awesome!) however, when connected to BTCGuild NONE of them show anywhere close to 2 Th/s.  They show more like 200 Gh/s.  I have 2 that are over 1 Th/s, but the rest between 0 - 278 GH/s.  WTF Bitmain?