HELP PLEASE sr20det crank no start issue but has spark and fuel

[s14kyyy]

i have sr20det 1995 nissan 240sx with crank no start but weird thing is car ran perfect 2 hours before i developed this issue. prior to all this i pulled the engine just to paint the bay and do a clutch. i reinstalled the engine and harness cranked it had a rough idle, fixed some vacuum leaks and had it running perfect. i shut it off came back about 2 hours later try to start it, crank no start . checked spark have good spark across all 4 check compression i have good compression checked fuel I’m getting fuel and injectors are firing i checked by pulling the fuel rail. im completely stumped my only guess is its getting to much fuel but idk when i pull the spark plugs there wet and black and smell like fuel. also after trying to crank it for 3 hours i got a REALLY loud back fire heres my mods 90k mile sr20 blacktop (red valve cover came off a different car) Garett t28 sr20 turbo, Tomei fuel pressure regulator, Greddy front mount intercooler, Hks Blow off valve, ISR exhaust manifold, Isr downpipe, Isr blast pipe exhaust, Tuned on mega squirt ecu, Aem air/fuel ratio gauge,

[AZhitman]

Sounds like injectors are dumping fuel (backfire). What's the FPR set to?