Dt466e fuel pressure problem

Hello all,

Working on my first electronic International engine and needing some help. It's a 1999 DT466e.

Truck starts fine but can't be driven because it loses all power at about 1500 rpm. I checked the pre-filter screen and the check valve (ball) and they seem fine. To be safe I also replaced the fuel filter.

I tested the fuel pressure via the Schrader valve and it's just at 40psi and the needle bounces pretty good. When I get on the accelerator, pressure dips a bit and the engine stumbles.

I can get the fuel pressure to go up to almost 50psi (truck not running) but it then looses pressure and PSI drops to 20psi or so.

One video I found describing a similar condition resolved the problem of bouncing fuel pressure at 40psi or so via replacing the lift pump. Could my lift pump be introducing air into the system?

Another thought is that the fuel pressure regulator (behind the head) is bad. Could that be the problem?

Would appreciate any thoughts on this. Thanks

A.