Thanks wicked. I think I'll try and get my datascan configured for the U13. This Bluebird SSS is my daughters car (ashpash), mine is a 300zxTT. Nissans rule!
If the diagnosis doesn't help I'll start with the ignition leads and plugs and go back from there.
From searching this forum it sounds like an ignition problem, but I also wonder its the fuel pump. It only happens when the motor warms up.
Btw - great forum. I'm with aus300zx.com so I guess I'm a visiting cousin.
Thanks for your help.