I bought a pre owned Pasquini 90 Auto, and am learning the machine. I noticed water coming out of the relief valve (?) into the drip tray while pulling shots. Most shots are a little fast, or don't pull at all (while water comes out the valve). I haven't been able to pull a proper time/volume shot, and wonder if the valve is not allowing enough pressure to build? Any input would be helpful.

We would need a lot more detail to really know what is going on.

The water you noticed flowing to the drip tray is probably from the OPV (over pressure valve) & that is normal. You want about 9 bar pressure during a shot. This can be checked with a pressure gauge or assuming that you have a vibe pump, approximated by measuring the OPV flow.

But it's more likely that your shots are too fast or choke due to an incorrect grind, stale coffee or distribution issues. You'd get better answers if you describe in detail how you are pulling a shot. In particular what grinder & coffee beans are you using, how fresh are they and how are you measuring & distributing the coffee?
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I have the Livia 90 and I just got the Baratza Vario grinder today. Do you have that grinder?

My experience over the past 4 years with this machine is that the finer your grind and the firmer your tamp, the more water comes out of the OPV and the faster your drip tray fills up. I have ground coffee so fine and packed it so hard that it just drips out at mega-slow rates and 10 times more water flows out the OPV into the drip tray. I've used crappy grinders and crappy coffee and literally as of tonight, I got the PERFECT shot on the first try with Store bought Peet's Italian roast, and the slider of the Baratza in the midlle of the espresso setting ( on the right) and in the middle of the fine setting (on the left). I noticed that the espresso came out at the "right looking" speed and there was not much water coming out the OPV.

The other thing is are you using the small basket or the monster basket? Throw away the monster basket if you are using it. The small or medium baskets work much better. (Can get them on http://www.pasquini.com)

Anyway, let me know if any of that helps.