Oh okay, I see. Fairly decent read ahead...
Honestly, with the IAT and timing you're at, you should be pushing upwards of 22psi on those 17t's before you start seeing rail pressure struggle. First thing I'd suggest is fixing your ethanol blend and making sure you're calculating correctly before fill-up. Next, I'd hate to say that you may need to claim a warranty with FCP over your HPFP and swap it for another one since it's a genuine BMW pump, which is less likely to fail shortly after install vs a different brand's for a lower price. Since you bought it from FCP, it's under a lifetime warranty. Yeah that means more time having to remove & replace yet again, but at least it'll rather cost you time and not money, with how expensive they are.
Now, I dealt with the same exact issue you're dealing with on my setup: FBO + 19t's @ ~22psi of boost on E40 w/ ~11* timing. Pulled great, but rail pressure would crash to 900-1000psi and my STFT's would peg out in the +30s. Eventually, it would start to have some sputters up top, and then soon enough it would misfire hard enough to throw me in limp mode once the Winter / colder weather set in. This isn't good because it's basically a lean cut which will eventually put you out of a motor.
You have three options I suggest based on my experience:
-Bring it up to CD919 and tell him to do whatever he can to prevent this from recurring
-Fix your ethanol blend, especially if your tuner says the same
-Replace your HPFP with another genuine one, especially if your tuner suggests based off readings
Adding on to my situation, I went as far as buying a genuine HPFP, removing the little filter out of it before install + drilling a 1/16" bore through my fuel rail to allow for as much fuel flow possible, and putting in an ethanol content sensor to make sure I had spot-on blends. This was all based on my previous tuner's suggestion. Unfortunately, I saw no change and it seemed to be stumping him too which didn't make it any better. This brings me to my last suggestion for you: if all else fails, consider doing business with another tuner.
I say this because with what I mentioned about my situation and everything I did to try and fight it, it didn't make sense to me that I literally saw no change even after handfuls of revisions, not to mention seeing timing drops as far as -10* in multiple cylinders. It sucked because I did business with this person for a while, and they had me dialed in pretty solid with a 22psi E50 tune on the stock turbos which made me excited for the 19t tuning. But, their response times were slowing down significantly over those several months and the inconsistencies in each revision didn't make the situation any better.
Anyway, I started searching around and asking friends how they enjoyed services with whoever their tuner was and it led me to contacting DocVu. If switching to him didn't help, it'd be a win-lose because his response times are much faster though I'd have to continue troubleshooting what's causing the rail pressure to behave the way it was. Surprisingly though, aside from his super fast turnaround times making the dial-in take no more than 2 evenings, my timing drops were completely gone, and rail pressure looked amazing. Not to mention switching from my previous tuner's last file I loaded on, to DocVu's on the same fill-up and seeing the improvements listed. The quickest time he responded with a new revision was literally 5 minutes from the time I sent the email containing the datalog for the previous revision, and the longest I waited until I heard back from him was about an hour or two which was still awesome.
Now on E40, at ~21psi of boost w/ 13* timing up top in weather as cold as 30*F, fuel rail pressure still quickly recovers up to ~2300psi by redline, while my low pressure, STFT's, and timing still look clean. I'm encouraged I can push upwards of 23psi this Spring / Summer with this improvement.
Hopefully this helps, keep me updated.
