Im at a complete loss here. Ive been dealing with Fuel pressure issues for weeks on my 5.3 swap. Lots of Threads with this issue but no one has one set fix.

My fuel pressure has been dropping from 60 psi all the way to 42 sometimes 38. Only at WOT

Im currently running full return system JEGS LS1 fuel rails, Stock LS1 injectors, Hyperfuel 255lmp Fuel pump, to 10 micron Hyper-fuel Fuel Filter and Hyperfuel 44020 Fuel pressure Regulator. The feed line is all 6an lines. The return line is 6an from the pump to The original Hard return line (1987 Rx7) back to 6an, into the FPR then to the rail. The filter and pump are a month old and barely had any use. The hyperfuel regulator was just put on today. We thought because I used a shitty regulator at first that the issue. Clearly not.

Ive tried running it with and without the vacuum line attached. With it NOT attached it will stay at 60psi flooring it at idle. But when we put it onto the dyno the moment you floor it the guage drops dramatically to 42.

When it HAS vaccuum it will drop to 42 psi no matter if its on the dyno or just at idle

any help would be massively appreciated. I know there is tons of threads on this but I havent been able to get a definite answer from any of them about this issue.

 

Where is the gauge? Pics of the rails and regulator location?
The way you described your return setup is very confusing.

 

Tried posting a photo, waiting on approval from mod?

 

^^ What Joe said.

 

Use MS Paint, and draw us a simple diagram with labels on what's sitting where.

This should be pretty solvable..

 

Faulty pump or regulator. I was losing fuel pressure at WOT so I swapped a 255 for 450 and problem solved.

 

The easiest way I can think to test this without much work or tools would be to run a hose from the regulator return to a gas can and see if the pump flows the rated amount for 60 psi pressure and if it holds that pressure (if the pressure drops you have restriction in the return line). If it doesn't then test the feed line to see if the flow is right for no pressure. Then last would be back before the filter or right off the pump and try to find the restriction or if the pump is junk.

The other option is to move the gauge connection to right after the pump and see if it drops. If not move forward looking for the source of the drop.

 

Ended up switching back to the old returnless Corvette reg/filter setup and it holds pressure fine.

I wish I could draw something up but it says I need admin approval for a photo. The best I could explain how I had it is, the 10 micron fuel filter went after the pump on the feed side. Then directly to the driver side rail. Then out the passenger side fuel rail and into the left side of Regulator. The return line goes from the bottom of the regulator all the way back to the fuel hat. The right side of the regulator is plugged

i thought about the Hyperfuel regulator also being bad but those are some pretty **** odds to get 2 different bad regulators..

 

Sounds like the only variable there was your 10 micron fuel filter.
What filter was it.

 

It was this one. It says its recommended as a post filter in the description also https://hyperfuelsystems.com/products/46080/

 

Generally on a return style setup you want your fuel pressure regulator on the return line... that is how mine is setup and its been fine since I did it a few years ago..

factory hardline into -8 AN for feed into billet rail at drivers rear.. crossover on the front and then return on passenger rear to my AFPR mounted on fuse block bracket and then -6 line out of AFPR to the factory EVAP line that is now used as a return line.. (on an Fbody at least)

 

Maybe I am reading it wrong, but your post as to the way you have it run does not make a lot of sense. Like Majestic above, mine runs from the in-tank pump to the filter. From the filter into the fuel rail. Through the rail to the fuel pressure regulator. From the FPR back to the tank. The inlet for the fuel to the rails is on one side of the rails, and the FPR is mounted on the other side of the rail with a crossover between the 2 rails.

The fuel makes a complete loop.

Is this how you have it set-up?

 

There are several ways to do it. With or without a crossover, i went without and have the back of both rails feeding to my regulator and that then returns through the EVAP to the back of the car and connects to the factory return line by the axle. The main thing is you want the regulator after the fuel rails, so even when you key on engine off, all of the fuel flows passed the injectors. This way unless the pump isn't enough or your filter clogs, the injectors always have enough fuel to do their job and they just select to use the fuel or let it go passed.

 

I had it setup just like what you said with the regulator after the rails and on the return side. But im not sure what you mean by the crossover between the two rails.

The line comes out the driver side fuel rail into the left fitting of the regulator. The right fitting of the regulator is plugged and the bottom fitting runs to the return. Could i have it plumbed wrong and the bottom needed to be plugged not the right fitting?