I have also been experiencing low fuel pressure, somewhat similar to Larry DeCampís post.
Hopefully, this can shed some light on his issues as well.
I experience low fuel pressures during climb out with the mechanical fuel pump when I shut off the boost pump. By low pressure, I mean my Dynon D10 EMS indicates ď0Ē psig. The engine never misses a beat but it is very concerning. When I reach top of climb and push over, lean, accelerate, and throttle back, the fuel pressure comes back to normal (4-5 psig). If I engage the boost pump during climb out, pressure again comes back to normal. I replaced the fuel pressure sending unit but that didnít resolve the issue. I also bled the air out of the fuel pressure manifold that the pressure sending unit is plumbed to.
It all seemed to have started after I replaced the fuel pump because of the mandatory fuel pump service bulletin. I replaced the LW 15472 with a Tempest AF 15472. All documentation that I have found says that they are equivalent.
I have a Mattituck TMX 0-360 carbureted engine with fixed pitch prop on a RV-7, a Vans stock Facet pump, and Dynon D-10 EMS.