fuel pressure drop and not increasing under boost
 

I've been experiencing fuel pressure issue on my fd and cant figure it out.
I'm running a walbro 450 pump in stock hanger. rewired relay with 10 gauge wire. fuel labs mini for

at first the issue was pressure drop and not holding pressure after priming. it would to zero in seconds. I replaced the old aeromotive fpr with the fuel labs hoping it would fix all my issues and it only fixed the priming issue.
I've replaced fuel filter with brand new factory style repacement.
I put a vac gauge on brand new reference hose to brand new fpr and it does see positive pressure.
at idle I used a hand pump and pumped pressure into regulator and fuel pressure increased to almost 70 psi
I've check power to the bulk head on top of hanger and ot reads 13.8-14 volts under idle,load and when pressure drops
walbro only a few months and maybe 2,000 miles old tops!
any ideas guys? I'm stumped

What is the fuel pressure currently doing? Will the car start and idle?

Any chance the fuel feed/return lines are reversed on the FPR? If they are backwards you get all sorts of oddball stuff happening, low pressure for sure.

Dale

sorry should have posted that info
yes it does start and run. at idle like 43 psi or so.
have the return on bottom of fpr.
so pump feeds primary rail on back then goes to front of primary to secondary. then on back of secondary to side of fpr. then bottom of fpr to tank

also I should prob mention stock lines from pump to the firewall. then its -6 in engine bay with FFE rails

I believe that base pressure should be about 40-43psi so it should be lower when the car is idling technically. It sounds like a mechanical issue if you don't see any leaks anywhere. I would almost bet your fuel line on the fuel pump isn't tight or slipped off or something radical like that. You don't mention any flooding so I wouldn't think an injector would be stuck open. It sounds like you need to just tear into the system and see what's what.

yea no flooding.
hose was put on when new walbro was installed

probably not understanding but just to be clear... static fuel pressure s/b 43.5 or 3 BAR.
at idle, fuel pressure should read around 35.
if your pressure is not constant the most probable answer is a leak between the pump and the hardpipe.
turn on the the pump and listen at the tank. you may hear a flowing sound which would be a bypass due to a leak. the
the fuel level needs to be low. maybe drain most of it... easier than taking everything apart and finding that isn't the fix..

There are some knockoff fuel pumps out there, it's probably a good idea to double-check that yours flows as advertised. Attach a short length of fuel line directly from the pump's outlet (bypassing most of the factory lines) and use the pump to try filling a 5 gallon gas jug. Their site claims between 109-119 gallons/hour flow rate at 0 psi fuel pressure, that's about 1.8 - 2.0 gallons per minute. If the pump flows properly during that test, try something similar but using the return line so the pump needs to supply pressure and push fuel though the normal fuel system.

I would check the in tank hose, make sure you use fuel submersible fuel line. Regular fuel hose is not designed to have fuel on the outside of it and it will fall apart from the outside inward till it springs a leak. Also check the in tank fuel sock

I had my pump fail with a similar problem. Base pressure was fine but as boost built up, at some point, pressure stagnated.
It all was due to failure in the O ring and plastic part where the pump output goes into the metal bell fitting on the metal outlet pipe.
Cutting the Mazda quick connect off and replacing it with submersible fuel line and clamps permanently solve the problem for many year now.