Leaning out under boost

[91white240sx]

Ok i have a problem. this is what i'm working with. i have a blacktop s13 sr20det built bottom end, gt2871r, 850cc injectors, z32 mafs, enthalphy rom tune ecu, walbro 255. Here is my problem, for some reason my car leans out under boost. i took it to a shop and they put it on a dyno with a wideband to see if my gauges were correct and as soon as i start boosting (3800rpm) it starts to lean out big time. I had the fuel pressure set to 44psi (vac line on) at idle, also i tried turning it up to 56psi and still same situation. could it be voltage drop to the fuel pump, my nismo fpr, or just the pump is going out? i want to see what everyone thinks and point me in the right direction before i start wasting money i don't have. Thanks in advanced

[bardabe]

I say check the Voltage on the Fuel Pump make sure it dosent drop. if the voltage is fine I say maby your pump is going out. I mean Walbro pumps are not exacly the best you know. you get waht you pay for 99$ for a fuel pump is not the greatest so ti can also be your Fuel pump going out. because 56Psi at idle with the Vac line hooked up is alot. considering that stock the FP is what 36 - 38 Psi. (not exacly sure don;t got access to FSM right now)