Just like the subject, what does it do, and do I need it? I'm replacing my broke stocker with a 255LPH, does the Pulsator need to stay in, or can I bypass it with the rubber hose supplied? The car will be runnig by tommorrow night I need info fast.

you don't need it get rid of it!!

If it is in good condition, you might want to consider keeping it. At higher line pressures (like many of us tend to try) the pressure spikes created by the pump can overcome the valving in the injectors and create problems. Check with Shadow on his opinion, or contact Rich at Cruzin' Performance.

If you're curious, the noise we normally hear from the fuel pump is caused by pressure pulses, so the factory wasn't wrong in installing a "miniature accumulator" to even out the pressure pulses a bit.