I need some help diagnosing a fuel pressure problem. I have a Vortech boosted 383 LT-1 with additional injectors at the throttle body. I also have pod-mounted boost and fuel pressure guages and a mityvac for testing. The problem is that fuel pressure tracks with vacuum ok up until boost reads '0', then when I get on it and into boost the pressure stays at the same level.

Specific diagnostic readings:

FP at idle (18 inches Hg) 39 psi

FP at '0' vacuum 47 psi

FP at 5lbs boost 47 psi (should be 47 plus 5 = 52).
FP at 10lbs bost 47psi (s/b 47 plus 10 = 57 psi)

I have tested the FP regulator at idle - applying 10lbs pressure with mityvac gives 57psi at the pod guage.

I have tested and fixed all vacuum leaks (I had a couple of slow leaks due to old connectors) - all vac lines from intake hold pressure without leaking down.

I cleaned all harness connections and earth connections plus the positive wire 'cluster' behind the batter. voltage at the FP connector at idle is 13.6V.

I replaced the fuel pump with a new Walbro (thanks Greg)

I replaced the fuel filter as a maintenance item 2,000 miles ago. I am going to replace it again.

Now I am at a loss what the problem could be. I suspect maybe a fuel line blockage, but I am very suspicious that the FP does not track with boost at all.

Any suggestions appreciated!