I just picked up a 1715 for my 01 and in the instructions is says to disable the fuel system before loaded or unloading a tune from the tuner or major engine damage my happen. Any one know why or what damage can be cuased?

 

The fuel pump runs when you have the ignition turned on. From what I understand while the SC is reprogramming the PCM it can cause higher than normal fuel pressure and that can cause damage. That's what I understand anyhow.

 

I think you are 100% correct!!!
I had to be the rebel and try it with out pulling the fuse/relay and sure as death and taxs the pump was running full blast the whole time!