Erratic/Fluctuating Fuel Pressure CA18DET

So I am hoping this video link below works. Here is my issue.

I have a CA18DET fitted in my old RA23 Celica.

Just as my car comes on boost (around 4-4.5K RPM) it goes flat, at 5K it takes off. I thought it was the PCV that was stuck, but this only partly solved the issue. I then checked the fuel pressure. Pressure is at 40ish psi (vacuum disconnected), but erratic.

Here's the weird thing....

When it is connected to the fuel tank return it is erratic.
When it is connected to the fuel tank return but disconnected at the tank, it is erratic.
When the return goes back to a tub (coke Bottle) it is fine.
When the return goes back to a tub (coke Bottle), trying lots of different sized restrictions, it is fine.

WTF! Any ideas?

I do have a new regulator on the way, but this just seems odd.

https://photos.app.goo.gl/FMJHRMgYeiBKG45E9

Fuel pump or fpr


Sent from my iPhone using Tapatalk

The fuel pump is an external Walbro bought new, although doesn't mean its not knackered, but seems to pump really well. I have a Voltage at pump of 13.4V when running.

I am hoping it is the regulator, I have just picked a new one up, so will fit it tonight. It just seems weird that it fluctuates only when feeding back through the fuel return pipes, yet if I try to replicate a restriction into a bottle it is fine.

Fitted new FPR, its 90% better, but there is still a light fluctuation. I would expect a rock steady reading at idle.