I needed the same info. (94 Olds Ciera S 3100 SFI)
Even though this is a really old post I thought I'd add to it in case someone was looking for the same thing that I was today.
In my Haynes manual, and everywhere else I've looked online, the Schraeder valve is on the throttle body side of the fuel rail near the fuel pressure regulator. On the 3100 it's on the other side crammed in between the power steering reservoir and the alternator. The cap was black plastic and had a white line scribed across it. I was afraid that it was some sort of pintle type screw adjustment. I braved loosening it with pliers noting how many CCW turns I'd made but no big deal it's just a cap.
pic attached.