What if a northern Andean civilization, probably post-Chavin, had developed a more advanced naval package and preempted the colonisation of the south Pacific from the Polynesians? The Polynesian colonisation of Easter Island and the sailing of the Kontiki prove it to be possible, though the vast distances and few islands in the south-eastern Pacific would make it difficult, but I don't think impossible.
So, perhaps a wave of Andean navigators expanding westward would collide with the Polynesians expanding to the east. I'd like the Andeans to at least get Hawaii before the Polynesians do.
This then raises the question of what manner of trade items and diseases would be exchanged in the process. This would mean likely a very long and distant Columbian exchange from a relatively early point in history (assuming the Sea-Chavin and the Polynesians make contact around after 200AD, somewhere in central Polynesia). The trade and interaction would be slight, but possibly maintained over a long period of time. This could see potatos and other Andean crops making their way across the Pacific, and maybe pigs making their way to the New World.
A bonus effect could be the Sea-Chavin exploring up the coast to California and planting agriculture there, but that may be less likely.