hard to say without seeing it. but if the grip safety used to work (meaning it would prevent the hammer from falling when its not depressed) and the ONLY thing changed was the sear spring, it may just be the spring or how it was put together. The grip safety, when the gun is not being held, has to be pushed back so the "foot" sits in the way of the trigger stirrup.
You could try putting more of a bend in the right most leaf of the spring - the one that holds the grip safety back. For that leaf of the sear spring, you cant really over do it, well, you can go too far, but not really. When the grip safety is pressed and released, it should positively be pushed back out when you let go. It should have some slight pressure to do so - driven by the sear spring. If no material has been taken off the grip safety "foot" (the part that pushes on the trigger stirrup preventing motion) then it should still work. Try putting a greater bend in that leaf - thus keeping the grip safety rearward when the gun is not held in a shooting position - and the foot in the way of the trigger stirrup - and see if that works. If that does not, you may need a new grip safety and fit the "foot." Also note, when the grip safety is not depressed - and you press the trigger with the hammer cocked, there should be slight to NO movement of the trigger, and def NO movement of the sear and hammer. Alternatively, subtle changes to how the sear is shaped can have a big impact on how the sear, disconnector, hammer, and grip safety all fit together to function. Good luck.
ETA: sorry, got some terminology wrong. Also might want to try dissaembling and reassembling the entire thing. Sometimes, despite lots of practice and familiarity, we assemble the things a little out of whack. Trying again - or rebooting - sometimes works.
This is a picture of the engagement of stirrup and grip safety. This would represent when the gun is not being held, and the grip safety is being pushed back, so the foot is down, in the way of the stirrup. When the gun is held for firing, the grip safety (and what I am calling its foot) is pushed up and out of the way of the stirrup.
Come to think of it, it could also be that even with the grip safety foot in the way, the trigger stirrup may travel far enough before it hits to foot to hit the sear and drop the hammer. That situation would require some new parts me thinks. Hard to tell.