TLDR: stock FPR is supposed to hold pressure for a long time, correct? And there's nothing between the "fuel-return-split-block" and FPR that could cause leakdown?

Details:
99T/A fuel system all stock except for Racetronix pump and hotwire kit, stock dead head etc...

Am trying to find out why I keep getting bubbles in my fuel when tested at the rail. Rebuilt the pump/hoses/bucket etc.. confirmed the bucket is not running dry.

When I swap out my stock bucket/pump assembly (still untouched) problem does not seem to appear, at least I haven't seen it yet.

With Racetronix bucket setup it does appear, an entirely different bucket/pump/pressure regulator etc. This is during DD driving, like sitting in a McDonalds drive through then parking for a few minutes, will have a hard start. I also suspect this caused a low fuel condition at the track last fall.

One main difference between the two is that the stock one does not bleed down when key off. The Racetronix setup does, and does so very quickly like in seconds.

Working theory is that car gets hot, pressure bleeds down before car gets a chance to cool down and now uncompressed gasoline has super low boiling point (like 140 degrees). Causes occasional hard starts and clear visible large gaps of air burping from fuel rail.

As a test, I uncapped the fuel pump relay (so I can have granular finger control and not overpressurize things), and totally blocked off the RETURN just after the split junction block (pic below). I then baby-tapped the relay to get the pressure up (jumped up to 80 almost instantly, a long prime might have blew out my plug LOL), and clearly the pump itself has a check valve that is HOLDING. The pressure stayed for a long time, like many many minutes. I believe this proves the pump check valve is OK and I don't have an injector or anything leaking down.

Please confirm this is a valid test indicating I need a new fuel pressure regulator in the tank. I believe the FPR in the tank is supposed to not leak down, but when this return is attached it does. This current FPR does hold stable 60PSI when running at all times,even WOT. I don't think there's anything else in between this junction and the FPR, right? There are zero fuel leaks and no gas smell anywhere.

Thanks...

 

Welp, zero replies so decided to make the jump last night.

Since I know all the Amazon $15 ones are surely junk, bought a Wells branded lifetime one from Advance Auto, about quadruple the price. Little more than Rockauto even after the %15 fuel perks LOL.. but at least I have some support if I need to exchange (Rockauto has literally zero support you can chat with or email or call or whatever, been burned).

Looks like a quality piece, but there is a rubber oring on the inside nipple that confused me. Here is a pic of the old one that DID NOT have the oring on the nipple, I just put it there for the illustration. I was very careful when I removed it and no oring present. I looked and probed inside the hole and did not see an old one still in there.I did try to install the new one with the oring, but it did not fit. So I removed the oring and the new FPR fit nice and tight, had to use channel locks to hold it while I put the clip back on.

But bottom line is this has fixed my leakdown problem. In my mind I was blaming the Racetronix pump since the FPR was holding PSI correctly otherwise, but with this new FPR it holds at 60 for a long time, and I think holds at 30 perpetually. Now to see if my bubbles remain.

I also need to confirm my tuning as I understand this will likely be slightly different PSI either UP or DOWN.. not sure how exact these things are part to part.