When it comes to squeezing every ounce of power, efficiency, and reliability out of your 6.6L Duramax diesel engine—whether it’s an LB7, LLY, LBZ, LMM, or LML—your fuel system is one of the most important upgrades you can make.
That’s where a FASS (Fuel Air Separation System) comes in. For owners of 2001 to 2016 GMC or Chevy trucks with the 6.6 liter Duramax, installing a FASS fuel system can be a game-changing modification with long-term benefits for both performance and longevity.
1. Solving a Fundamental Weakness in the Duramax Fuel System
One of the biggest shortcomings of the factory Duramax setup is the lack of a factory lift pump.
Unlike its Cummins counterpart, the Duramax relies solely on the CP3 or CP4 injection pump to draw fuel all the way from the tank. This puts unnecessary strain on the pump, increases cavitation, and can shorten the life of expensive components.
A FASS Fuel System solves this by incorporating a high-efficiency lift pump that maintains consistent fuel pressure, reduces injector pump stress, drastically improves fuel quality, and helps extend the life of your injection system.
2. Superior Air and Contaminant Separation
Air and vapor in diesel fuel can cause poor combustion, injector damage, power loss, and reduced fuel mileage. FASS uses a unique air/vapor separation process that ensures only pure, clean fuel reaches your CP3/CP4 pump and injectors. This leads to:
- Increased fuel lubricity by at least 10%
- 3x the life of injection components
- Optimized MPG
- Restored horsepower
- Sharper throttle response
- Smoother engine operation
- Reduced soot output
This is especially valuable on older LB7 or LLY-equipped trucks where injector failure is a common (and costly) issue.
3. Improved Fuel Filtration
Diesel fuel is notoriously contaminated with water, dirt, and more. A FASS Diesel Fuel System features industry-leading fuel filters that provide:
- Over 99% water removal
- The FASS Extreme Water Separator also acts as a fail-safe—preventing catastrophic damage in the event you get a heavily contaminated batch of fuel.
- Debris filtration down to 2 Microns absolute
This extreme level of fuel filtration can save you thousands in repairs over the lifespan of your truck.
4. Increased Power and Fuel Economy
While gains will vary depending on supporting modifications, many Duramax owners report noticeable improvements in power and MPG after installing a FASS Diesel Fuel System.
With more reliable, consistent fuel delivery, restored injection timing, and cleaner combustion, your engine can make more efficient power.
You’ll also likely see a bump in fuel economy—especially under load or during towing—because the engine isn’t compensating for poor fuel atomization or altered injection timing.
5. Essential for Tuned and Modified Trucks
If you’ve added a tuner, larger injectors, or upgraded your turbo, a stock fuel system can quickly become a bottleneck. A FASS Diesel Fuel System ensures your fuel delivery can keep up with increased demand, protecting your investment and helping your truck reach its full performance potential.
6. Peace of Mind and Long-Term Value
Duramax trucks are built to last, and many owners plan to keep them well past the 300,000 or 400,000-mile mark. A FASS Diesel Fuel System is a preventative upgrade that protects your CP3/CP4 pump, injectors, and overall engine health.
It can also increase resale value for buyers who understand diesel performance.
Final Thoughts
Whether you’re daily driving, towing heavy, or building a high-performance truck, a FASS Diesel Fuel System is one of the most practical and beneficial upgrades for any 2001–2016 GMC Sierra or Chevrolet Silverado with the 6.6 Duramax.
It corrects key factory flaws, enhances reliability, supports power mods, and ultimately makes your truck run cleaner and stronger.
In short: If you want your Duramax to last longer, run better, and perform at its best—a FASS Diesel Fuel System is a no-brainer.
Pro Tip : Pair your FASS System with a Single-Bolt Fuel Sump to make installation easier than ever!
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