fallen of the path

i just got a quick question whenever i de celerate my car backfires violently i bult my own turbo system in a 90’ 240sx and i have the safc for fuel management now when i accelerate sometimes there is more power than other times so i was just wondering if it was maybe timing too much fuel, too little fuel was makin pwer unpredictabe or something else are the bacfiring and any of these things related
steer me in the right directions please somebody

Is your blow off valve vented to atmosphere?

do you still have ur cat?