So, the car is all back together, fuel pressure is set at 2.5 Bar (confirmed with external gauge as I didn't trust the plumbed in gauge) starts and runs absolutely fine, no misfire at all.

However when I'm out in the car and it starts making boost, feels totally fine until it hits 0.5 - 0.6 bar boost. At which point it feels like the ignition cuts. Not a misfire, definite ignition cut.

I can see fuel pressure rising with boost, and at 0.5 Bar boost, fuel pressure is 3 bar.

Anyone have any ideas? Car feels great apart from this.