I found this fic when I was very very diehard 1x4x1.
Title: Tears in the Rain
Pairing: Potential future 1+4/1x4 (undecided)
The story so far involves a missing Quatre Winner, a Heero Yuy sent to investigate an incident at a manufacturing facility, and Newtype themes.
I found it on ff.net where it was last updated 5 July 2003.
Very realistic and intriguing and appeals to the inner 1x4x1 fangirl as well as the geeky wanna-be engineer.
The silver lining is the author confesses to being notoriously slow - five chapters in two years - so my fingers are crossed for the appearance of chapter 6 sometime in 2004.