FASS DIFSHD4001 Drop-In Series Diesel Fuel System for Cummins ISX/X15

The FASS DIFSHD4001 Drop-In Series Diesel Fuel System is purpose-built for medium and heavy-duty Cummins ISX and X15 diesel applications. Designed as a true bolt-in upgrade, this Fuel Air Separation System (FASS) delivers world-class filtration and improved fuel delivery without requiring cutting, wiring, or additional modifications.

Modern diesel injection systems are highly sensitive to fuel contamination. Water, entrained air, and particulate debris can cause premature wear and catastrophic failure of expensive injection components. The FASS DIFSHD4001 eliminates these threats by filtering debris and entrained air down to 2 microns, while removing over 99% of water from the fuel supply — protecting your injection pump and injectors for the long haul.

Key Features:

• Filters fuel to 2 microns — removes debris, entrained air, and air vapor
• Third-party proven to remove over 99% of water from diesel fuel
• Increases fuel lubricity by at least 10% by eliminating entrained air and vapor
• True plug-and-play installation — no cutting, wiring, or tuning changes required
• Installs in one hour or less — driveway-friendly bolt-in upgrade
• Flexible mounting: inlet ports and air separation ports usable on either side
• Single outlet port located on top of the filter base for clean routing
• Extreme Water Separator (XWS) filter acts as a failsafe dam — shuts engine down before water damage can occur
• Exclusive Performance Radius Cuts (PRC) in the aluminum housing promote smooth fuel flow and prevent eddy currents
• Retains full functionality of the OEM Water-In-Fuel (WIF) sensor
• 50-state emissions legal with CARB E.O. number on metal label
• Backed by FASS limited lifetime warranty

Unlike competitors that rely on square 90-degree and T-bone fittings — which can restrict flow and reintroduce air — FASS's exclusive Performance Radius Cuts keep fuel moving freely through the system. The result is cleaner fuel delivery, improved throttle response, restored horsepower, and optimized fuel economy (results may vary).

The FASS DIFSHD4001 offers the same industry-leading filtration performance found in the full Titanium Signature Series line, in a simplified drop-in format designed specifically for heavy-duty Cummins platforms.