It’s very easy to kink the fuel line in the saddle tank design if you don’t run messenger line to pull the ejector pump line to the right place

This is described with photos in the xc90 forum by user shockwave

autozone might have a loaner fuel pressure guage to try.
But it probably needs testing under load, got vida?

Pull the fuel pump out again and inspect the hoses for kinks. Shockwave had the dealer install his pump and they kinked it, twice. It was a gnarly one to diagnose as it would periodically unlink and work well.

We have indeed seen in-tank fuel hose kink, however you appear to say that direct power to the pump seems to solve the problem. Would suggest a fuel pressure gauge at the schrader valve to read the pressure live. The replacement PEM was used unit ? Always possible someone sold an already faulty one ...

Would suggest a fuel pressure gauge at the schrader valve to read the pressure Live ^^ This I don’t see any fuel rail pressure measurements with an independent gauge. That’s the missing data. When my PEM went I had no codes but the fuel pressure went to 52psi initially, after a minute started an os...

There is nothing complicated about a fuel pressure gauge. An air compressor tank gauge (0 to 100 psi) borrowed from an air tank will read what you need. Remove the valve from the schrader valve and connect with rubber hose and hose clamps. Be careful to have no leaks. No ignition source or flames. D...

Also, more basic things like the spark plugs and timing belt in good condition. If you want to keep looking for what may cause the fuel pressure to be low - but I recommend using used parts otherwise it will get too costly, may also look at the bottom contacts of the ECM (I put a video showing how t...

I understand your frustration. When things go bad, it is sometimes hard to get everything corrected again. In the case of the hard plastic fuel lines, once they are kinked, it is hard to get them round again. Perhaps some mild heat can get the kink out of the tube. Maybe there is a replacement tube ...

The pump might be losing its prime. It should be submerged to get proper cooling from the gas.

Did the car run OK for at least part of a test drive immediately after new pump install? I am asking because many times on P2 models when the pump is removed dirt gets into tank. Fine dust silty stuff that ends up on top of tank. There is a fine mesh cloth filter on bottom of pump inside that pump b...