I am baffled and afraid to get on my car right now. I recently installed a Tsudo header and after installing my wideband is now showing I am running lean(~13.5) under low boost(~3psi).

Things of note:
I read about 14.7 at idle, looks normal.
I have recalibrated the wideband to make sure there wasn't an issue there.
The header doesn't appear to have any exhaust leaks.
The header now reads cylinder 4 instead of the collector like on the stock header.
The new bung on the s pipe is quite a bit shorter than the one that came with the kit. The o2 sits more in the exhaust than before.
Have reset the computer twice.
Have removed the unichip and put the stock pulley on to verify, still reading lean.
New plugs recently installed.
Secondary o2 mounted with cel eliminator.

Do you think I have a real lean issue with the header or is it more likely I have an exhaust leak I do not see or I need a different longer bung for my wideband and I am getting a bad reading?

 

The first thing I thought was, recalibrate, but it looks like you covered everything. Do you have an OBD reader, my wideband and OBD sometimes have different readings. I am planning on adding the tsudo header to my setup soon, so I would also like to know what is going on.

 

when you installed the header did you replace the crush gasket from the header to the spipe?

 

If TQ has increased in that range, this could be possible. This means that more air flow is present. More air requires more fuel to maintain the same AFR.

The stock header is quite restrictive, and I am sure this new header and s-pipe combo flows a lot more than the stock therefore needing adjustment on your tune.

 

I sure did, even put some ultra copper between the donut and the header, this is the under side of the donut not the rounded side.

I am going to run it for a little while and see if I can find any exhaust leaks from carbon build up. As Paul said I just may really be running lean.