No Products in the Cart
If you’re towing Utah’s canyons or just want your 6.7L Cummins to feel calmer in traffic, you’ve probably heard a dozen different takes on FASS systems—some helpful, some… creative. This article is our no-drama breakdown from the service bay: what a FASS changes, what it doesn’t, and when it’s the right (or wrong) first move.
A FASS (Fuel Air Separation System) filters finer, separates water/air, and stabilizes supply pressure feeding your high-pressure pump. Those things can make your truck run more consistently—but that’s not the same as bolting on free MPG.
Air/vapor removal: Aerated fuel makes rail pressure “hunt.” Smoother rail can mean cleaner combustion and slightly better cruise efficiency on steady highway runs.
Stable inlet pressure: The CP3/CP4 doesn’t work as hard when supply pressure doesn’t sag. Lower parasitic load and steadier injection events can net small gains on long freeway stints.
Cleaner filtration: Precise injector tips like clean fuel. Healthy spray patterns support efficient burn, which helps MPG over the long haul.
Towing weight, speed, and headwinds dwarf modest efficiency gains from a lift-pump system.
Right foot + terrain dominate fuel economy in Utah. Holding 70 vs. 80 MPH over Parley’s is worth more than any pump change.
Tune & gearing set the baseline. FASS won’t fix a calibration that dumps fuel below boost.
Bottom line: Expect consistency and the possibility of modest, situational improvements—not a guaranteed MPG jump. Choose FASS primarily for drivability and component protection.
“Will it sound like a leaf blower under the bed?” Short answer: no—if installed properly.
Outside / near the tank: A soft electric hum at idle.
Inside the cab: With factory sound deadening and the truck moving, most owners report little to no change. You may notice it faintly with doors open in a quiet garage.
Use isolation bushings on the bracket.
Mount off the cab sheet metal (we favor frame-rail locations that don’t resonate the cabin).
Route flex sections in the feed/return to reduce transmitted vibration.
Prime the system and verify no aeration—aerated pumps can sound louder.
Result: Civilized outside, practically invisible inside.
A FASS helps the parts you care about most: injectors and the high-pressure pump.
Finer filtration reduces abrasive wear at injector tips and pump plungers.
Water separation cuts corrosion risk; easy draining means you actually do it.
Stable supply pressure keeps the CP3/CP4 from cavitating or overheating itself trying to meet rail targets.
Air removal prevents the “starve → surge” cycle that feels like hiccups on grades.
Not a cure-all: If a CP4 is already shedding metal or injectors are worn, FASS is prevention, not resurrection. It shines when added before there’s a problem—and when filters are serviced on time.
“FASS guarantees +2–3 MPG.”
Myth. It can help consistency; the big knobs are speed, load, and tune.
“It’s loud in the cab.”
Myth. Poor installs can be boomy. Proper isolation makes it barely noticeable inside.
“It fixes every hard-start.”
Myth. If hard starts come from weak batteries, glow/grid issues, or a failing HP pump, address those first. FASS helps air-in-fuel problems, not electrical or compression issues.
“You can skip filter changes because it’s better filtration.”
Myth. Better media protects better—if you replace it. In Utah winters or dusty conditions, shorten intervals.
“It adds power.”
Myth (mostly). It supports power you already command by stabilizing fuel delivery. You’ll feel smoother torque, not a new peak number.
Known fuel contamination: Fix the tank/source and purge the system before adding anything.
Obvious charge-air leaks: Boost leaks make the tune dump fuel below boost; fix leaks first.
Weak batteries / grid heater issues: No lift pump solves low cranking RPM or dead cells.
Mismatched turbo/tune: A smoky, hot setup needs calibration and air-side health—not just more fuel supply.
Bone-stock, low-miles, light duty: If your truck is truly stable and you don’t tow, you can prioritize other upgrades (intercooler, monitoring). We’ll still test supply pressure for peace of mind.
Before we recommend anything, we like to measure:
Supply pressure test (idle and short load pull)
Filter condition and a fast look for water/debris
Road log correlation (throttle vs. rail behavior)
If you’re towing: optional EGT snapshot to see how steady fueling behaves on a grade
You’ll get a simple result: Healthy / Service & Retest / Upgrade Recommended—with transparent pricing for FASS, filters, and any supporting hardware (draw straw, lines) tailored to your 6.7L.
Get a Same-Week Fuel Health Check
Quick test, clear plan. If FASS makes sense, we’ll price the right kit and book your install. Financing available.
If the cause is aeration or marginal supply pressure, it can help a lot. If the issue is batteries, grid heater, injector return leakdown, or a tired HP pump, we’ll address those first. That’s why we test.
Most owners stay within the lines by using quality parts, keeping emissions equipment intact, and documenting professional installation and filter maintenance. We provide paperwork for your records.
Usually no. On mild builds and daily/tow use, the standard, well-routed kit is correct. Bigger fueling/injector setups may benefit from different pickup/line strategies—we’ll spec that based on your goals.
MPG: Maybe a little, mostly via consistency—not a guarantee.
Noise: Properly installed = quiet inside, soft hum outside.
Reliability: Real protection for injectors and the CP3/CP4—if you service filters on time.
Best candidates: Towing at altitude, summer heat, tunes/injectors, long-term ownership.
Ready to find out if FASS is right for your 6.7L?
Book a Fuel Health Check and we’ll make the call together—data first, parts second.
