Whenever my Z see's above 4K rpm's It feels like it hits a brick wall . It
starts sputtering and missing . On the scanmaster the O2's read between
600 and mid 700's at WOT . I know thats extremely lean . Every once
in a while it wont sputter or miss at WOT and the scanmaster's O2
readings will read MID 800's to HIGH 900's . I havent put a fuel gauge
on it yet to check fuel pressure . What do you guys think it may be ???
Thanks

 

Ignition. Possibly optispark, but more likely wires. If you have headers, even more so likely a burnt spark plug wire.

Certainly check fuel pressure, but an O2 sensor doesn't read rich/lean, it reads how much oxygen is around, and if its a lot, calls it lean. When you have a misfire, you have unused oxygen AND extra fuel in the exhaust, but the O2 sensor just sees the oxygen and calls it lean.

 

Had the same problem last year and plug wires were only 5k miles old and at night could not see any arching from them at all. Replaced wires and problem corrected. Thats my story, hopefully your problem is simple also.

 

It didnt start doing this till it sat for 6 months . Any other opinions ???

P.S.- Theres no engine codes thrown either .

 

I just bought a new coil several months ago, everything appeared fine. THen the EXACT symptoms you described started happening. I replaced the coil with my old stock one and it worked perfectly right after in the 4000 rpm plus range. At night my coil was arcing VERY slightly so i didnt think much of it, but i suppose it was arching way way more at higher RPM for some reason.

The "New" Coil that did this wasnt coated in anything. THe old coil that still worked was coated in a rubbery stuff which i guess was to prevent such arcing from happening.

Hope this helps and possibly solves your problem It does sound ignition related.