[lextrueno]

I've got quite the challenging problem.
2013 Scion FRS; NA tuned and in process of setting up Flex Fuel.

I was going through some tuning revisions with Zach from CSG and needed to fill up to a full tank of gas. After filling up, I got on the highway and did a pull for datalogging successfully with no anomalies. Shortly after completing the pull, no more than 5 minutes. The car outright dies. After pulling over and checking for anything catastrophic like a window in the block. I tried starting the car. Never kicked over, just kept spinning the engine. Zach later confirmed no issues with the tune, everything looked fine. After towing the car home a few hours later, I was able to start the car in my garage with 0 tricks/gimmicks. However upon starting, the car bogged and immediately dies. I datalogged the event, and it shows .4MPa at the fuel rail reducing to .1MPa when the car dies. So that tells me the fuel pressure sensor is reading fuel; and that there isn't enough getting to the rail as it should be 4Mpa for idle.

Before I did anything, I swapped my Walbro basket from when I was boosted; to an OEM one. I had the basket on hand and figured it could be an easy fix/swap. Hoping that would clear up the issues. No luck. Same issue. So after taking some measurements right before the HPFP; I verified 58psi - .4MPa was coming from the basket and into the HPFP.

I just installed a junkyard HPFP hoping that would clear up the issues but no luck again. Same exact issue. Car starts right up and immediately bogs out due to no fuel. Upon reading the codes, I only get an EVAP code P0451. I don't believe that should be creating the issue I'm seeing but maybe I'm wrong. When I was boosted, I had hard pinned the EVAP hoses underneath the manifold so I will double check with a boroscope and see if any popped off. Since the issue is HP/Basket fuel pump agnostic, I have a hard time trying to figure out where to look next. If the fuel rail pressure sensor was bad, I should have more codes.

Any suggestions or ideas?