My buddy put a new fuel rail on his s2k. Fuel pressure was fine for a day. Now when he gives it any throttle his fuel pressure gauge spikes to a 100. That's all his gauge goes up to. Pulled the vacuum line off the regulator to see if it was working. With the vacuum line on he's getting 40 psi and with it off he sees a 100. So he's fpr is working fine. I think I'm missing something here.

 

im fairly certain you have to run an aftermarket fuel pressure regulator with that rail