Although my vehicle is a 180SX, i use Skyline steering rack and piping as i run an RB25, I have a similar problem with mine but i have a solution.
My problem is the same as yours. My rack is from a 4 wheel steer model, the system runs a "booster" solinoid for when the engine is running at low rpm i.e parking. to assist with the low system pressure. I performed a check of my system and my car doesn't run the solinoid "booster".
The fix in my case is to use a rack from an S13. Not sure if your rear steer has been disabled, or removed altogether, but this may help you narrow it down.
Hope it helps