After a year of searching this problem still not totally fixed, after fuel pump swap, mechanic changing all relevant sensors from our cars R34 to c34 then adding NISMO fuel pressure reg, running on dyno (mixtures are good), fault is much better. Car is detonating occasionally causing the ECU to put the car into the knock limp mode, this limp mode does not bring up an engine check light. Has anyone else had issues like this? I am still trying to find root cause, not just work around yet. Thanks also to those who posted!