I got fooled years ago with the oil pressure sensor on a 1995 Magnum 5.9 V8.
I wanted to know the actual pressures at different needle positions on the stock dash gauge..
I left my sensor in place and bought a replacement oil sensor and rigged up an adapter with bleed off valve to connect to a tire valve expecting to create and then read from zero to 50 psi using air pressure from a tire.
The stock Dodge sensor “cuts off” suddenly at low pressures.
You might have 8 psi but the output will be zero.

Perhaps this was designed in prior to OBD-I computers to trigger a dash light.