Fuel Pressure specs?
 

According to Bentley, my fuel pressure should be around 40+ psi.

I installed an aftermarket fuel pump recently (Dephi). With the fuel pressure regulator vacuum hosed connected, it only yields 30psi.

Without the fuel pressure regulator hose, it yields 40psi.

Is this normal? Or is the fuel pump out of spec?

I'd think it's unlikely for the pump to be bad. Have you tested the regular by applying and removing vacuum via hand bleeder?

EDIT: I just tested mine and I'm getting similar results. I get 35 psi regulator on, 45 regulator off. I'm having hesitation problems though. I'm changing the O2 sensors today because these M44 engines are very finicky.

Spec should be 3 bar - 43.5psi, with the vacuum line off. With the line connected, the regulator should decrease by manifold pressure. If its not making this pressure, it can be the regulator, pump or filter issue.

So if its at spec with the line disconnected, re-connect the line with a T-fitting to a vacuum gauge and the engine running. The fuel if the gauge reads 10psi vacuum, the fuel pressure should be 33.5psi. If not, the regulator is bad.

I noticed that in the Haynes manual for e36. The car was off in the test so the regulator didn't change anything. So my fuel pressure is good, but I might have flow issues or intake leak or bad sensors.