I recently finished building a 1976 Datsun 280z. 5.3, t56 magnum, single 7875 turbo running Terminator X with DBW.

I have driven the car a handful of times and I am having an intermittent odd issue with the fuel pressure.

Fuel system specs:
2000 Camaro V6 fuel tank
New Herko replacement fuel bucket
Walbro 595 fuel pump F90000295
10ga wire from battery to pump
Holley Hydramat 3x15 part 16-111
8AN feed and return PTFE fuel lines with section of Nicopp hard line
Deatschwerks 8-03-110-005K-8 5 micron fuel filter
Radium 20-0589 Split-Flow Flex Fuel Sensor Adapter
Radium 20-0534 Universal Check Valve
GM 13577429 - Flex Fuel Sensor
Racetronix fuel regulator set to 44psi, bolted to inner fender
Fasster fuel rails
522-128X Holley injectors

Flow path:
Tank->hydramat->pump->filter->check valve->flex fuel sensor->fuel rail inlet->fuel rail outlet->fuel pressure regulator->return line to tank




The fuel pressure regulator pressure port is connected to the intake manifold via 6mmID tubing on a shared line with the BOV (highlighted in yellow)


Car is being tuned by Dr. EFI. Running pump gas. Fuel pressure set to 44psi. Just running off wastegate springs right now (8psi falling to 6psi)
I have only driven the car a few times before winter set in. Out of the few times I have driven it the fuel pressure has dropped sharply from 44 psi to 15psi. This isn't a gradual drop, it's very sharp. It has only happened in 2nd gear for whatever reason. When it happens, the car instantly loses all power. Then inexplicably, after I let off and get back in it, during the 3rd gear pull it's steady up to 6k. Car was running 1/2 tank of gas during the pull.
I've attached a log file to show what I am taking about.

So far I have toggled the fuel pump on in the software with the engine off and wiggled the wire connector at the tank but didn't have any audible effect.

I'm not sure what to try next. I can jump the fuel pump relay and datalog fuel pressure in my garage while tinkering with the system but can't drive the car again until spring.

There are no leaks that I can see.

Potential things I can think of that could maybe cause pressure issues:
Flexible tube from pump to bucket head not sealed tightly
Debris in lines somewhere
Very small leak
Faulty regulator
Electrical issue
Tune issue
Issue with vacuum line from manifold to regulator

Not sure how to troubleshoot this. Really odd that the pressure would drop in 2nd gear but hold 3rd all the way to 6k with no issues. Also the car was very recently finished so I haven't driven it that much. But I really want to try and fix this issue over winter.

Any comments or advice welcome. Please help!

Thanks

 

Go back into your datalog and look at your voltage over the same pull and see if it drops.

 

5 microns filtration might be a little TIGHT for a high flow fuel system.

I've seen alternators cut OFF at very high rotor speed.

I have a particularly rev happy 4.8 Liter that runs a larger diameter Alternator pulley.
Slowed down alternator 30% still charges 100 amps at idle.

 

-Put the flex sensor on the return line.
-Consider an increase to a 10-micron filter, or get a much larger 5 micron filter.
-Those check valve fittings are terrible.
-Make sure voltage isn't dropping at higher RPM.
-Anything Racetronix

 

Thanks everyone. Great suggestions. I checked the voltage in the tune and it was rock solid.
I am willing to change anything that is the issue but was really hoping I could troubleshoot instead of just swapping in new parts one at a time.

Does anyone think that I could determine if any of these suggestions are the culprit by jumping the fuel pump to let it run and logging fuel pressure without running the engine or driving the car?

Still the biggest question in my mind is what would be a likely culprit of a problem that only occurs intermittently? That has me thinking about a faulty pressure regulator or a loose connection inside the tank.

Screenshots of the datalog (fuel pressure in white)

Entire pull (2nd and 3rd)


Only the 2nd gear portion of the pull: