Every once in a while someone expects me to say something different than what I’m about to say. But here’s the truth:
If you own a 2017+ L5P Duramax, your factory in-tank lift pump is actually pretty solid.
I work at FASS Diesel Fuel Systems, and yes — we build aftermarket fuel systems for a living. But the reality is that the L5P Duramax came from the factory with one of the better fuel supply setups GM has ever used.
The stock lift pump on these trucks provides surprisingly strong fuel flow, even when the truck is tuned or lightly modified. And that leads to an important point.
The Real Problem Isn’t Fuel Flow
When people start looking at aftermarket fuel systems, they often assume the biggest benefit is
increased fuel flow. On older trucks, that was often true.
But with the 2017+ L5P Duramax, the factory pump already moves a healthy amount of fuel. Even many tuned trucks still aren’t pushing past the limits of that pump.
So if the pump flows enough fuel… what’s the problem? The answer is fuel
quality.
Modern high-pressure common rail injection systems are extremely sensitive to contamination. Tiny debris, water in fuel, and air intrusion can slowly damage injectors and pumps over time. That’s where the
real improvement comes from.
Why We Developed the L5P Drop-In Fuel System
At FASS, we looked at the L5P platform and asked a simple question:
“If the factory pump already flows enough fuel, what do these trucks actually need?”
The answer was better filtration and fuel conditioning, not necessarily more flow. That’s exactly why we developed the
FASS Drop-In Series Fuel Systemfor the 2017+ L5P Duramax.
Instead of replacing the factory lift pump, our
Drop-In System works alongside it, dramatically improving the quality of fuel reaching the injection system.
What the Drop-In System Actually Improves
With the FASS Drop-In Fuel System installed, L5P owners gain:
- 2-micron absolute filtration
- Air and vapor separation
- Over 99% water removal
- Improved fuel lubricity by at least 10%
- TRIPLE the life out of your injection system
All while retaining the factory pump’s strong fuel flow. This makes it an ideal solution for stock trucks and many modified trucks as well.
When Do You Actually Need More Fuel Flow?
Now, if you’re building a high-horsepower L5P with large injectors, big turbo upgrades, or competition-level power, then yes — additional fuel flow can absolutely become necessary.
But the majority of daily driven and tuned L5Ps simply don’t reach that point. For those trucks, improving fuel filtration and conditioning is the upgrade that makes the most sense.
The Bottom Line
The 2017+ L5P Duramax factory lift pump deserves more credit than it gets. It flows plenty of fuel for most stock and moderately modified trucks. What these engines truly benefit from iscleaner, air-free fuel.
That’s exactly why we designed the
FASS Drop-In Fuel System— to dramatically improve filtration while letting the factory pump continue doing what it already does well. Sometimes the best upgrade isn’t replacing something that works.
It’s improving what matters most.
