EFI Fuel Filters: Micron Ratings & Placement — The No-Drama Setup
AN Hose 101 • Hot Rod AN
Quick answer (EFI): Use the in-tank sock as your inlet pre-filter (no extra 100 µm needed). If you run an external pump without a sock, add a ~100 µm pre-filter on the inlet. Always run a ≤10 µm post-filter between the pump and rails.
Quick answer (Carb): After the pump, use a ~40 µm filter or finer (e.g., 10 µm) so long as the element area maintains flow at WOT. Inlet protection can be a sock or coarse screen.
Hose construction: Stainless braided = stainless-steel outer braid → PTFE core.
Nylon braided = nylon outer jacket → stainless-steel outer braid → PTFE core. Filtering guidance below applies to both styles.
Nylon braided = nylon outer jacket → stainless-steel outer braid → PTFE core. Filtering guidance below applies to both styles.
- Why micron & placement matter
- How fine is “fine”? (flow & restriction)
- Proven plumbing layouts + diagrams
- Choose the right element by fuel
- Line & pump sizing by HP & fuel
- Mounting, routing & service
- Troubleshooting: symptoms → fixes
- Parts & recommended products
- FAQ (click to expand)
Why micron rating & placement matter
Micron measures particle size (1 µm = one-millionth of a meter). The pump inlet needs low restriction — that’s what the sock or coarse screen is for. On the pressure side, protect injectors and carb needles/seats with fine filtration. For EFI, that means a ≤10 µm post-filter. For carb, ~40 µm works well or go finer (10 µm) if the element area supports flow.
How fine is “fine”? (flow & restriction)
- Inlet side (sock/coarse): Prevents starvation and cavitation at the pump. If no sock, use ~100 µm stainless pre-filter.
- Pressure side (fine): EFI injectors prefer ≤10 µm. Carb can run ~40 µm or finer if element area supports WOT flow.
- Element area matters: A larger, finer element can outflow a small, coarse one. Don’t undersize the housing.
Proven plumbing layouts + diagrams
Return-style EFI (regulator on the rail or return line)
Let the sock (or coarse screen) guard the inlet. Mount the ≤10 µm post-filter after the pump, before the rails. The regulator returns excess fuel to the tank.
Returnless with filter/regulator (“Corvette” style ~58 psi)
Use the sock for inlet protection; if none, add a ~100 µm pre-filter before the pump. Mount the filter/regulator near the tank, then run a single feed line forward.
Choose the right element by fuel
- Pump gas (E0–E10): Microglass/synthetic or high-quality cellulose elements work for ≤10 µm EFI post-filtration.
- E85 / alcohol blends: Prefer microglass/synthetic or stainless. Avoid plain cellulose/paper (swelling and breakdown risks).
- Pre-filters (~100 µm): Only needed if there’s no sock. Stainless mesh is ideal: low restriction and serviceable.
Line & pump sizing by HP & fuel (quick guidance)
- Rule-of-thumb flow: Gas engines need roughly LPH ≈ HP ÷ 10 at pressure. E85 typically needs ~×1.3 the flow.
- Common low-side lines: AN-6 feed to ~500 HP; AN-8 for ~500–800 HP; AN-10 for higher/long runs. E85 often benefits from stepping up one size.
- Gen V LT note: Covers the low-side only (feeds the high-pressure pump). Filtration still follows: sock/coarse inlet, fine post-pump.
Mounting, routing & service
- Location: Sock/coarse at inlet; fine post-filter after pump, before rails/carb. Keep away from exhaust heat and road debris.
- Clamps & spacing: Secure lines with insulated clamps (12–18" typical). Use proper clamps & mounts.
- Orientation & arrows: Follow the flow arrow. Horizontal/vertical is usually fine if the element stays primed where applicable.
- Service intervals: Inspect/replace elements with your oil-change cadence; shorten intervals with E85, dirty tanks, or fresh builds.
Troubleshooting: symptoms → likely cause → fix
| Symptom | Likely cause | Fix |
|---|---|---|
| Pump noisy / hot | Fine filter on inlet; clogged sock; kinked feed; undersized wiring | Move fine filter post-pump; clean/replace sock; fix kinks; verify voltage under load |
| WOT lean, pressure drops | Post-filter too small/clogged; pump undersized; restrictive fittings | Upsize/replace post-filter; verify pump flow & wiring; check AN adapter flow path |
| Fuel smell in garage | Old rubber hose permeation; loose flare; vent issues | Upgrade to PTFE hose; re-seat AN flares; verify tank vent routing |
| Injector clogging / misfire | Coarse element after pump; contamination from new tank/lines | Install ≤10 µm post-filter; flush/clean tank; replace element |
Parts & recommended products
- Fuel Filters (all) — pick ≤10 µm for EFI post-pump; ~40 µm (or finer) for carb post-pump; ~100 µm only if you don’t have an in-tank sock.
- Factory-Style Inline Filter/Regulator Kit (AN-6) — fixed ~58 psi regulator + filter in one; ideal for returnless LS plumbing near the tank.
- Replacement Fuel Filter Element — service the factory-style unit without re-plumbing.
- PTFE Hose & Fittings Bundles — nylon-jacketed or stainless braided options (both with PTFE core).
- AN Adapter Fittings — GM quick-connect to AN, ORB-to-AN, NPT-to-AN, and more.
- Gauge/Pressure Port AN Adapter — add a diagnostic port after the post-filter.
- Clamps & Mounting Hardware — secure, serviceable installs.
FAQ (click to expand)
Do I still need a 100 µm filter if my in-tank pump has a sock?
No. The sock is your coarse pre-filter, so you don’t need an additional 100 µm inlet filter. You still need a post-pump filter: EFI = ≤10 µm; Carb = ~40 µm (or finer like 10 µm if the element area maintains flow at WOT). If you have no sock (external pump), use a ~100 µm pre-filter before the pump.
Where should I measure fuel pressure?
Add a gauge/diagnostic port after the post-filter and before the rails. That reading reflects what the injectors actually see.
What micron ratings should I use for EFI?
Sock or ~100 µm at the inlet (if no sock). Then a ≤10 µm post-pump filter before the rails. Fine filtration belongs on the pressure side.
What micron rating should I use for carbureted systems?
After the pump, use a ~40 µm filter or finer (e.g., 10 µm) so long as the element area is large enough to avoid restriction at wide-open throttle.
Nylon vs stainless braided hose — what’s the difference?
Construction: Stainless braided = stainless-steel outer braid → PTFE core. Nylon braided = nylon outer jacket → stainless-steel outer braid → PTFE core. Nylon is friendlier to paint and handling; stainless is tougher near abrasion/heat. Same filtration rules apply.
Can I put the fine (≤10 µm) filter before the pump?
No. A fine inlet filter increases restriction, promotes cavitation, and overheats the pump. Keep the inlet sock/coarse and place the fine element after the pump.
Scope note: Hot Rod AN PTFE hose is not supplied for brake or power-steering applications. Exclude AN-4 in your parts planning (we do not stock AN-4).
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