Whats the difference between ISFJ and INFJ

ISFJs have these functions:
Si

Fe
Ti
Ne 

INFJs have:
Ni
Fe
Ti
Se

Pretty different. INFJs utilize Ni as their dominant function, which focuses more on probability and intuition. Ni is about seeing the many possibilities and condensing that information into one, final outcome. Think like a funnel going out, sucking everything....and then condensing all that into one thing, funnel in. 
We ISFJs utilize Si, which has to do with making past connections to various things and using that information to make decisions based on the present and future. We rarely ever forget anything. We always tend to remember the past. INFJs are not that great with the past and tend to dislike the past, being more future oriented.

Great site I found would be this:
http://www.keys2cognition.com/explore.htm




Perceiving—how we focus our attention and gather information
Cognitive ProcessBasic (Passive) UseDeveloped (Active) Use
extraverted Sensing (Se)Notice sensory data in the environment.Trust your instincts and take action relevant to the moment and current context.
introverted Sensing (Si)Recall tangible data and experiences.Stabilize a situation by comparing it to what is expected, known and reliable.
extraverted Intuiting (Ne)Notice abstract patterns as they emerge.Shift a situation's dynamics and explore imaginative potential possibilities.
introverted Intuiting (Ni)Receive "ah-ha" insights and realizations.Persue a greater level of awareness to transform who you are and how you think.
Judging—how we organize our experiences and make decisions
Cognitive ProcessBasic (Passive) UseDeveloped (Active) Use
extraverted Thinking (Te)Follow steps, points and time tables.Create structure, reason by measures and evidence, and implement complex plans.
introverted Thinking (Ti)Adhere to definitions and impersonal principles.Analyze a problem using a framework, and find an angle or leverage by which to solve it.
extraverted Feeling (Fe)Honor others' needs and preferences.Connect with people by sharing values and taking on their needs as yours.
introverted Feeling (Fi)Adhere to personal beliefs about what's important.Evalute situations and choose what you believe is congruent with your personal identity.