No fuel pressure

I'm totally stumped. I've been searching the forums and so far no luck fixing my issue.

I have an 08 MS3, replaced the engine with a jdm import about 2 months ago. Car was running great, then had a stalling issue when it was hot. Fuel pressure was holding, then dropped to 3 psi and car stalled. Managed to get it restarted, drove for a bit then same issue. Had it towed home, sat over night, started with no issues. A few days later, same thing.

I have since replaced the fuel pump, tested the resistor (no issue there), checked all wiring, swapped HPFP with the one from old engine, swapped fuel pressure relief valve,, and checked all fuses, relays, and wiring. Can't get the fuel pressure to get over 5psi. Really not sure where to go from here. Is there a test procedure to make sure I getting the right voltages at the fuel pump harness? Any help at this point would be greatly appreciated.

 

update: jumpered the terminals at the fuel pump, pump runs. So my issue is somewhere in the wiring. Tested all fuses, no problems. Guess I'll need to pull the wiring diagram and start tracing back the wiring.

 

Welcome to forum. You will need to tell more about car. Profile page to start at least. Much much more data on the car. Everything you can think of. Actual condition of everything. So many interdependent things can cause your troubles. History needs to be more in depth on why was engine replaced. What you are using to measure the 5 psi fuel pressure.
More info here is the way to get more responses.

 

Engine was replaced due to previous owner snapping the timing chain. Figured it was more cost effective to replace then engine than tear down the original and search for more internal damage. Car has 190k on it. I've pulled all fuses and checked, everything is good. All wiring looks good, no obvious signs of damage. If I jumper from a 12v source at the relay the fuel pump turns on, however car still won't start. Checking fuel pressure on the Torque app and a manual fuel guage both show only 5 psi. Car ran great after the engine swap, and then about a month and a half later this fuel issue developed. Not really sure where to look at this point

 

Pull the pump assembly out of the tank and verify that the filter isn't completely clogged and that all of the lines are connected inside the basket

Is there gas in the car?