I have a 98 neon that has developed a fair size leak near the rear passenger-side tire only when pumping gas. Can some give some information the cause for this and possibly the name of the part I would need to fix/replace in order to stop this? Thank you in advance!

 

It's gotta be the filler neck, but it is odd that you havent gotten a code that reads you have a massive evap leak (A hole would cause the pressure test to fail, thus reading a leak). Crawl under the car and look to where the gas cap is (but on the car side). Search everything, look for heavy corrosion and holes. There will be a pipe that directs fuel to the tank and a smaller one that is for the canister. On my 2000 its corroded but not busted, yet. And you say leak I'm assuming its gas right? Lol.

 

While you are under there, may I suggest that you look at the fuel lines. As part way down the length of the car (roughly under the rear passenger seat) there is a metal plate across the fuel and brake lines this plate tends to trap dirt and water so they like to rust there also.