ENFPs and ENFJs are superficially similar. They often end up at the same place. They just get there by very different routes.
ENFPs love brainstorming, encountering new ideas, etc. They often change interests and careers. They are not persuaders, but champions of their beliefs, so that others follow their examples as they are inspired. Their example persuades others more than their arguments.
ENFJs are friendly, outgoing, persuasive. They are natural teachers. If they champion a cause, they convince others tofollow through their words (cult leader style, almost).
ENFPs lead with Ne and like all Ne doms, can appear to be random, at times. Fi keeps them strongly true to their personal values. They love ideas, concepts, etc.
ENFJs are people oriented, understanding the emotional level of every one else around them and how best to connect with them. They guide the group and push the group in their desired direction. ENFJs tend to love ideas and concepts as well, but in a way that ideas impact people.
ENFPs and ENFJs act very differently when stressed.
The Ni vs Ne issue is huge, as in the Fe vs Fi issue.