[ossiblue]

Good that you have Tony on board with this--he knows his stuff through lots of hands-on experience.

From you initial results, no change in system and cold control pressure, the problem is looking to be a blockage in the return path to the tank. This could be a fault with the WUR or a blockage in the return line. The most likely problem is with the WUR as your system pressure is within spec and if the there was no fuel at all returning to the tank, the pressure would likely be closer to 6 bars if you have a stock pump (which I know you don't.)

Regardless of what your initial results appear to be, perform all of the tests Tony has listed and post the results. If your fuel tests confirm the pressure never change from the high value of system pressure, you can begin work in locating the area of obstruction.