Help me understand fuel pressure differences at rail and regulator

[sportinawoody]

Fore return style setup, I set fuel pressure at 43.5 on the regulator and in the tune to match. My question regards what scanner reports under fuel rail pressure and fuel pressure from my FRPS vs fore regulator. at idle i see 38 frp vs 43.5 I set the ragulator at with vacuum disconnected. 1st, should i still have vacuum running to the frps ? It is relocated in the y block that feeds the rails if that matters. also there is very little change from cruising to getting into boost on my fuel rail sensor. I have all filters and logic turned off right now along with forced OL to dial in the air/fuel and LWFM. fuel is fat but maintains under wot. fuel rail pressure vs fuel pressure seems to stay the same also

[decipha]

http://efidynotuning.com/inj.htm

[sportinawoody]

I read that and understand what the regulator does under different MAP's. I'm asking about logged FP vs logged FRP differential vs regulator pressure and should i trust logged pressure vs disregarding the fore mechanical gauge when setting pressure as they are quite a ways apart and also should FP and FRP differential ideally stay relatively close to the same ?

[decipha]

A mechanical gauge with no manifold reference and only atmosphere reference as is common is only going to show you absolute rail pressure and not injection pressure. So it will fluctuate since under vac the regulator has to reduce the absolute rail pressure and in boost the regulator has to raise the absolute rail pressure in order to maintain a constant non changing delta injection pressure so the actual fuel pressure remains constant under vac or boost and doesnt fluctuate.

[sportinawoody]

I can not for the life of me deduct an answer to my question although that is very helpful information, thanks. I'm still wondering if I set absolute pressure correctly by using what my frps reported to vcm scanner as fuel pressure at idle vs the what my fore regulator gauge was reporting since they are not reading the same. I did the process the same at idle with manifold reference disconnected.

[decipha]

absolute pressure is a useless variable unless you have manifold vac or boost pressure to know the actual injection pressure

as long as you have a manifold reference line on the frps then i would trust it to be more accurate