Somebody please step me through the spring replacement. Adding a spring for more psi.

 

not sure about the fass but on the airdog you pull the fitting out of the return port on pump and spring is behind that.

 

Dieselram is right.Remove the return fitting off the pump and its behind there.Becareful and don't drop the rubber ball that goes behind the spring.Its very simple.The spring seats the ball against the return port.If the pressure is higher than the springs rating it pushes the ball away and allows excess pressure to bleed back to the tank,when you need all the fuel flow to maintain pressure the ball blocks the return port.

 

The return line fitting correct.