I am more than confortable running my truck at said pressure (12-14 PSI) every day with never an issue. 12 PIS will not hurt anything. NOW why is it dropping...that is the question here....
A 95 GPH pump can push more pressure than a 150 GPH pump. This is due to you load a motor by 3 things:
Volume, Fuel Viscosity, and Pressure.
We can assume that the fuel is diesel so the viscosity is a constant in this situation.
Say you have 10 amps of use out of the motor. You start with high volume...you are going to eat up quite a bit of thoes amps with that. SO you only have a little left to use up for pressure.
NOW you reduce volume, you start off with less of a load....so you can run higher pressures before you reach the 10 amp mark.
BUT you can set pressure with in the range of the pump with just a spring. Volume has nothing to do with that aspect. But excessive volume is key to maintaining pressure. If you put more fuel to the injeciton pump than it can use, your pressure will not drop.
BUT outside elemenets can play into this as well. Restriction, both before and after the pump, gauge error, and regulator malfunction.
Im just running down the list to see if our gauge is now telling the truth. Which i have seen many lie in my 2.5 year i have been doing this for FASS. Once we have confirmed the gauge......we can move on to other things.....