Fuel pressure with a EP381

I've previously replaced the stock TBI fuel pump with the later model EP381 and with the mildly modified LO5 engine I think I managed to get 15.0 PSI from it at the time, which was all I needed.

When I changed to a Vortec crate motor with TBI on it I also went with an aftermarket 46mm throttle body with an adjustable fuel pressure regulator, I never had more than 15.5 PSI showing on the fuel pressure gauge even though the regulator was apparently set to 18 PSI when it was sent to me.

I had a go at cranking up the fuel pressure by winding up the adjusting screw but it didn't seem to make any difference at the time.

I normally get between 15-15.5 PSI constantly but my W.O.T DC injector % indicates I need more fuel pressure (Wideband AFR's are okay at W.O.T.).

Tonight I thought I'd have another go at increasing my fuel pressure, initially I wound the adjusting screw up another couple of full turns and changed the spring to one out of a stock throttle body that netted a drop to 13 PSI. I then without making any other changes put the spring back in that came with the adjustable regulator and I got 15.5 PSI again. I don't seem to have a lot of adjustment left and I've probably wound the screw up 5 full rotations without any noticeable change in fuel pressure. Anyone have any idea what might be going on, I'm assuming an EP381 can crank out more than 15.5 PSI?

The EP381 should dead head over 60 psi. It appears that the pump is capable of flow nearing 41 gal/hr. I found these specs online, so I can't confirm they are correct.
Though its very unlikely, its possible your fuel filter just isn't allowing enough flow through it. -Or something like a kinked line might be causing the problem.

Thanks for your thoughts, it has 15.5 PSI at idle and can maintain 15.5 PSI at W.O.T..
If it was a restriction I would have thought the fuel pressure would have dropped off as the demand increased under load.

What an exercise that was....I decided to have another go at increasing the fuel pressure.
Previously I couldn't get above 15.5 PSI, I knew the pump should be capable of it but because I was running out of thread on the adjusting screw I decided to add a spacer under the spring. I then adjusted it so that I fully compressed the internal spring to dead head the pump, I tested it for a couple of seconds by just turning the key on to start the fuel pump and sure enough that pegged my 30 PSI fuel pressure gauge.

I then backed off the adjusting screw one full turn and I had 21.5 PSI, I then preceded to pull the top off the injector pod and back off the adjusting screw one turn at a time until I had backed it off fully and I still had 20 PSI, it was at that point I realised when I pegged my 30 PSI gauge I must have damaged it internally because now it returned to 5 PSI not 0 PSI.
I pulled the regulator apart and made a smaller spacer to fit inside and reassembled it.
I then replaced the damaged gauge with an expensive (but suspect) liquid filled Holley fuel pressure gauge and it only read 10 PSI, top off the injector pod and turning the adjusting screw up one full turn at a time only got me up to a max of 14.5 PSI.
At that point I decided to retire that gauge from service.
I was determined not to let this beat me tonight so I pulled apart another 60 PSI fuel pressure gauge and managed to install that. I backed of the adjusting screw to a mid point and checked the pressure, this time when I turned on the key it showed 16 PSI. I once again went through the procedure of pulling the top off the injector pod and winding up the adjusting screw on full turn at a time until I got up to 17.5 PSI (one full turn was about .4 PSI)
I then started the engine, it took a couple of seconds to clear itself and I had to hold the revs up slightly to help it do that but once cleared it settled to an okay idle and the fuel pressure gauge finally read 18 PSI :-)
I must have pulled the top off the injector pod at least 20 times!

I've adjusted the "Injector Flow Rate (TBI lb/hr)" in TunerPro to compensate for the increased injector flow.
I used the calculator at WitchHunter Performance and it came back with 72 lb/hr for my stock 61 lb/hr injectors @ 18 PSI.
Hopefully I'll get a chance to test drive it tomorrow.