What is my fuel pressure problem?

I am out of ideas of what could be my fuel pressure issue. The car will start with about 48psi but it jumps all over the place. After about a minute and a half running the pressure just slowly drops until it is only reading about 5psi. This fuel setup on the car worked with no issues before I bought the car not running. It previously had twin Bosch 044 inline pumps. 10an lines from the fuel tank to the split to the pumps. From my research the pumps on the car were at least 6 years old. I run e-85 in it so I wanted new pumps. I went with the AEM 400s to replace the 044s. I had the issue before swapping to the new pumps. I also replaced the FPR and fuel pressure sensor hoping one of those would be the issue. I have no leaks anywhere and voltage to the pumps when running is a steady 14.3v no matter the pressure. I'll attach a drive link with a log file of the car idling and pictures of the fuel setup. The car is a SW20 MR2 with a built 3s.

https://drive.google.com/drive/folders/1XtYC-29QyOnGQcq_E84sd8MBQIfL4-LA?usp=sharing

Hi Kyle

To me it would seem that your fuel supply to the pumps is being restricted.

Maybe in tank filter or strainer is clogged up.

Are you referencing your fuel pressure regulator from the same place as your MAP sensor?

How are your twin pumps fed? This style of pump doesn't like to draw fuel; they're designed to push, so having a filter before them isn't the best, nor is giving them a massive straw to suck through to get fuel to them.

Is this a track/drag car? If so, I'd get a swirl pot added to the system and have a 450 or bigger in-tank pump, then have as short a run as possible to these two pumps.

Have your filter in line from the tank to the swirl and, if possible, none from the swirl to the pumps.

I also try and get my customer to have a pre-rail fuel pressure sensor; these can show a lot more than regulator-mounted ones

I pulled the tank out of the car to check how the pickup was. I didn't know if it was using a lift pump or not either. The pickup wasn't clogged at all and I blew through all the fuel lines when I had the whole system apart.

Yes the FPR and map sensor are referenced from the same place. Each having a port directly on the side of the intake manifold. It is a drag car currently but I don't plan to race it really. I bought it for a fun weekend car.

At this point it almost has to be the feed to the pumps. I'm not sure who designed the system but the fuel pumps do sit much higher than the tank. The car did make over 800 with the same fuel setup but with the 044 pumps. I used the same micron filters as it had as well. I think I can rearrange the setup and get the pumps to sit as low I can to see if that fixes the problem. If that does work then I will plan on doing a fuel cell in the frunk and routing the lines differently.

I moved the pumps and filters to the garage floor. That didn't change anything at all. It still had an erratic fuel pressure then slowly dropping to under 10psi.

For funsies I swapped the old Bosch 044s on. The pressure was more stable for a couple minutes before slowly dropping. The pressure didn't drop near as fast with the Bosch pumps but still didn't last more than 3 minutes before the pressure drop. I didn't have my laptop to log anything. Tomorrow I'll take out the pre pump filter and see what that does.

Possibly a venting issue, have you tried leaving the fuel cap off and see if it does the same?

I have not tried that. It's getting late here and I don't want to bother the neighbors right now. I'll try doing that tomorrow along with removing the pre pump filter and hope for the best.

The problem ended up being the pre pump filter choking the pumps out. I removed that and it's all good now. Holding a steady pressure now and no dropping. What a headache! Just because things are new doesn't mean they are working. Thanks everyone for the help and ideas.