Throttle tip-in issue/stumble (3.0 5-speed)

[Effduration]

Would you please test fuel pressure after the Hengst installation? There was a bad batch of Hengst fuel pressure regulators (installed in filter) and I had one on my E39. It generated fuel pressure of 60psi causing the car to to run rich.

[andrewwynn]

It’s common for the filler/FPR to mask low output fuel pump. Did you ever estimate your engine on hours?

My money is on weak fuel pump.

Sadly a real pita to test there's no test port. You have to add in a T between the pump and filter (though not difficult if you have the under belly off from filter change)

[80stech]

That's pretty much all wrong andrewynn.
The filter and regulator can't mask a bad fuel pump, the test port is on the rail, that's the part that counts. Testing (pressure) between the pump and filter only would only give an indication of restriction (plugged fuel filter.) Testing at the rail and under load eliminates fuel supply as being a problem.