98 buick regal gs 3800 sg engine starts, runs a few seconds then dies, starts right back then dies

with fuel pressure gauge attached-key on reading 42 psi- start car reading 45 psi, needle ?Fluctuates violently then dropes to 0 car dies, pressure jumps back up to 45.starts right back up- duplicates problem,over and over.replaced regulator same problem, tried bypass trick on fuel pressure resistor-no help