Does the 400 have a max pressure spring or something. I remeber reading on here that some pumps would not go up in pressure due to a spring or something in the pump

 

I believe 100psi is their limit.

I could try capping off the return and priming the pump, this should build pressure in the system up to the point where the pump bypass opens to relieve the pressure.

Also I could try manually applying pressure to the regulator vac port to see if increases fuel pressure.

The lack of higher pressure in boost isn't a huge deal, with the 72# injectors and methanol injection the IDC doesn't get much past 60% at the moment. It's just annoying when things don't work like they should.

 

Did it work before with the other pump and that fuel rail setup

 

With stock regulator, Walbro 255, and stock wiring it would increase in boost at nearly 1:1 up to a point (~10psi boost) where the pump was insufficient and the fuel pressure stopped climbing and started to fall slightly. I think I saw up to 66-67psi of fuel pressure with this setup.

Then I swapped in a Walbro 400 with hot wire kit, new bucket (uncut), and a new plastic pump-to-module fuel feed line (rubber line sprang a leak) and it was overpowering the stock regulator giving a fuel pressure of ~65psi all the time even in vacuum and boost.

Then I swapped out the stock regulator and replaced it with the bypass plug and put the Aeromotive FPR in the return line. I had it set to 48psi base pressure initially but it wasn't maintaining that very well, so I bumped it up to 58psi yesterday. No pressure rise in boost at either base pressure.

 

Pinch off the return line, if pressure doesn't increase somethings wrong with the pump or the plastic line on the bucket.