Answer
Oct 28, 2025 - 03:20 PM
A "blue spring upgrade," such as the Sinister Diesel Blue Spring Kit with Adjustable Billet Spring Housing and Fuel Filter Cap for 2003-2007 models, refers to replacing the factory fuel pressure spring with a stiffer blue spring. This upgrade increases fuel pressure, helping improve injector performance, throttle response, and engine reliability. The blue color signifies its higher tension, making it easy to identify during installation or maintenance.
