The AEM 340LPH Fuel Pump: High-Flow Performance for Demanding Engines

The AEM 340LPH fuel pump is a high-performance electronic fuel pump designed to deliver a substantial 340 liters per hour (LPH) of fuel flow at specific pressures. It provides a reliable solution for engines modified with forced induction (turbochargers, superchargers), high-compression builds, nitrous oxide systems, or significant horsepower increases exceeding the capacity of most factory fuel pumps. This pump offers a significant flow upgrade over stock and many aftermarket "upgrade" pumps, ensuring adequate fuel supply to meet the demands of powerful engines, helping to prevent dangerous lean conditions under load.

Understanding Fuel Pump Flow Rates: LPH Explained

Fuel pump performance is primarily measured by its flow rate, expressed in liters per hour (LPH) or gallons per hour (GPH). This figure indicates the volume of fuel the pump can deliver within one hour under specified pressure conditions. The "340LPH" designation of the AEM pump clearly communicates its core capability: delivering 340 liters of fuel every hour. This flow rate is crucial. Insufficient fuel flow starves the engine, leading to lean air/fuel mixtures. Lean mixtures cause excessive heat, resulting in detonation (knock), damaged pistons, melted spark plugs, and catastrophic engine failure. The AEM 340LPH pump provides the volume needed to support significant horsepower gains safely.

Why Standard Pumps Fall Short for High-Performance Use

Most factory-installed fuel pumps are engineered to meet the exact requirements of the specific engine model they come in, often with minimal reserve capacity. Once you begin modifying the engine to produce substantially more power – whether through adding a turbocharger, installing a supercharger kit, building a high-compression naturally aspirated engine, or adding nitrous oxide – the factory fuel pump quickly becomes inadequate. Upgraded injectors, common in performance builds, also require more fuel volume behind them to operate at their increased flow potential. An insufficient pump becomes the bottleneck, restricting engine power and creating a serious risk of engine damage due to lean operation, especially at high RPM and wide-open throttle when fuel demand is greatest.

How the AEM 340LPH Addresses Performance Needs

The AEM 340LPH pump solves this problem by providing significantly higher flow capacity. An AEM 340LPH pump typically flows substantially more than many factory pumps (which might range from 120LPH to 200LPH depending on the vehicle) and also more than many lower-tier "upgrade" pumps marketed at 255LPH or 290LPH. This extra flow headroom ensures the fuel system can keep up with the increased demands of powerful engines. It allows tuners to safely increase boost pressure, advance ignition timing, or utilize larger fuel injectors without worrying about the fuel pump maxing out. The pump maintains consistent fuel pressure under load, which is essential for precise air/fuel ratio control by the engine management system, leading to optimal performance, efficiency, and engine longevity. This pump is known for supporting horsepower levels well into the 500+ wheel horsepower range in many common turbocharged four-cylinder and six-cylinder applications, making it a popular choice among enthusiasts.

Key Technical Specifications & Design

The AEM 340LPH in-tank fuel pump builds on proven design principles but incorporates enhancements for higher flow. Key specifications typically include:

  • Flow Rate: 340 Liters Per Hour (LPH) @ 40 PSI (free flow rates are often higher, but flow against pressure is the critical metric).
  • Voltage: Designed for standard vehicle 12-14 volt electrical systems.
  • Maximum Pressure Rating: Significantly higher than fuel pressure regulator settings (e.g., 100+ PSI), providing durability headroom.
  • Design: Modern high-flow variants often utilize a brushless DC motor design. Brushless motors offer key advantages: they typically run cooler, generate less electrical noise (which can interfere with sensitive engine sensors), and have significantly longer service life because they eliminate the brushes that wear out in traditional brushed motors. The pump assembly includes a filter sock at the inlet to prevent large debris from entering and causing damage.
  • Fitment: Available in various configurations to fit specific vehicle models. The most common is a "drop-in" style designed to replace the original in-tank pump assembly (often called a "bucket" or "hanger" assembly) in specific makes/models (e.g., Honda B/D/H series, Nissan KA/SR/RB, Toyota 2JZ, many GM models, Ford Mustangs, etc.). Universal versions are also available but require custom installation.
  • Inlet/Outlet: Usually designed with specific barbed or quick-connect fittings to integrate with the vehicle's existing fuel lines or common upgrade fuel hose sizes (-6AN is common).
  • Temperature Resistance: Engineered to withstand continuous submersion in gasoline at elevated temperatures found inside a fuel tank. Using non-fuel-rated pumps externally (especially not submersible) is extremely dangerous and should never be attempted with this pump.

Common Vehicle Applications (The Need for Flow)

The AEM 340LPH pump finds its home in a wide range of performance vehicles where increased fuel flow is non-negotiable:

  • Turbocharged/Supercharged Imports: Highly modified Honda Civics/Integras (B, D, H series engines), Acura RSX, Nissan 240SX (KA24DE, SR20DET), Nissan 350Z/370Z (VQ), Subaru WRX/STI (EJ series), Mitsubishi Lancer Evolution (4G63), Mazda RX-7/MX-5 Turbo builds.
  • Muscle Cars & Trucks: Turbocharged/V8-swapped Ford Mustangs (Foxbody, SN95, New Edge), GM F-body (Camaro/Firebird LS turbo builds), LS-powered trucks, Dodge Challenger/Charger (Hemispheres with boost).
  • Drift & Track Cars: High-revving, high-load engines that demand consistent fuel supply.
  • Nitrous Oxide Equipped Vehicles: Large nitrous shots require a massive instantaneous increase in fuel delivery.
  • High Horsepower Naturally Aspirated Builds: Large-displacement, high-RPM engines with aggressive camshafts and high-flow injectors.
  • Hybrid/E85 Conversions: Ethanol (E85) requires approximately 30-35% more fuel volume than gasoline for the same power output. A pump that was borderline on gasoline will be insufficient on E85. The 340LPH pump provides the necessary volume margin for safe E85 operation, especially on higher horsepower builds. Always confirm pump compatibility with specific ethanol blends.
  • Replacement for Overworked Smaller Pumps: Vehicles where a previously installed 255LPH or 290LPH pump is no longer sufficient due to further power upgrades.

Installation Process & Critical Considerations

Proper installation is paramount for the safe and reliable operation of any high-flow fuel pump, including the AEM 340LPH. Here’s an overview of key steps and critical points:

  1. Preparation (Safety First):

    • Relieve fuel system pressure before starting (consult service manual - procedures vary but often involve pulling a fuel pump fuse/relay and running the engine until it stalls).
    • Disconnect the vehicle's negative battery terminal.
    • Work in a well-ventilated area away from sparks/open flames. Have a fire extinguisher readily available.
    • Syphon or drain the fuel tank to a low level (ideally below 1/4 tank) before removal.

  2. Accessing the Fuel Pump:

    • Locate the fuel pump access panel (often under the rear seat) or prepare to lower the fuel tank if access is underneath. Follow the specific vehicle's repair procedures. Removing seats or cargo area trim is common.

  3. Removing the Old Assembly:

    • Carefully disconnect the electrical connector and fuel lines from the pump module/hanger assembly. Be prepared for residual fuel spillage – have absorbent rags ready.
    • Remove the locking ring securing the pump assembly. Special tools (fuel pump lock ring wrenches) are often required and prevent damage. Do NOT use screwdrivers and hammers.
    • Carefully lift the assembly out of the tank, paying attention to the float arm for the fuel level sender. Avoid bending this arm.

  4. Transferring Components & Installing the AEM Pump:

    • *Crucial Step:* On "drop-in" kits, you will transfer your existing components (fuel level sender unit, float arm, sometimes the outer casing or specific mounts) from the old assembly to the new AEM assembly. FOLLOW THE INSTRUCTIONS PROVIDED WITH THE PUMP KIT PRECISELY. Transferring incorrectly can lead to inaccurate fuel gauge readings or improper fitment.
    • Ensure the pump filter sock is securely attached to the pump inlet tube.
    • Verify all O-rings and seals between the assembly and the tank are in perfect condition and properly lubricated with clean engine oil or silicone grease designed for fuel systems. Never use petroleum-based grease. Replace any damaged or deteriorated seals immediately.

  5. Reinstallation:

    • Carefully lower the new assembly into the tank, aligning it correctly. Ensure the float arm moves freely and doesn't bind.
    • Hand-tighten the locking ring initially, then use the proper tool to torque it securely to the manufacturer's specification. Overtightening can crack the assembly or tank flange; undertightening can cause dangerous fuel leaks.
    • Reconnect the electrical connector and fuel lines securely. Double-check all connections.

  6. Electrical Considerations:

    • High-flow pumps draw more electrical current than stock pumps.
    • Strong Recommendation: Install a dedicated wiring upgrade kit. This involves running thicker gauge wires directly from the battery (through a fuse) and a relay triggered by the original fuel pump signal wire to power the pump. This ensures the pump receives adequate voltage (minimizing voltage drop) and protects the vehicle's factory wiring from overheating, melting, or causing a fire. The AEM 340LPH will not reach its full flow potential on undersized factory wiring. Ignoring this can lead to pump failure and reduced performance.

  7. Final Checks and Priming:

    • Reconnect the battery negative terminal.
    • Turn the ignition key to the "ON" position (not start) several times. You should hear the pump run for 2-3 seconds each time to prime the system. Listen for smooth operation. Inspect thoroughly for any fuel leaks at all connections and around the pump flange/lock ring area before lowering the tank or replacing access covers. DO NOT START THE ENGINE IF YOU SEE OR SMELL ANY FUEL LEAK. Rectify immediately.
    • Only once you confirm no leaks, start the engine and check for smooth idling. Double-check again for leaks under pressure.

Why Wiring Upgrades Are Non-Negotiable

This point is so critical it deserves its own emphasis. Factory fuel pump wiring is generally sized precisely for the current draw of the original pump. The AEM 340LPH pump requires significantly more power (amperage) to operate. Attempting to run it through the stock wiring harness has serious consequences:

  • Voltage Drop: Excessive resistance in thin factory wires causes a significant drop in voltage reaching the pump. Lower voltage means the pump motor spins slower, directly reducing its output flow and pressure. You won't get the full 340LPH performance you paid for. This defeats the purpose of the upgrade.
  • Overheating Wiring: The wires themselves become overloaded, heating up dangerously. This can melt wire insulation, damage connectors, and poses a severe fire risk within the vehicle.
  • OEM Relay/Fuse Failure: The stock fuel pump relay and fuse are not designed to handle the higher current draw, potentially leading to premature failure (car won't start, stalls) or, worse, a melted relay/fuse box.
  • Pump Strain & Premature Failure: Consistently running a high-flow pump on inadequate voltage forces it to work harder, generates excess heat, and drastically shortens its lifespan.

Installing a dedicated relay kit with properly sized wiring (often 10 or 8 gauge) directly from the battery ensures the pump gets full voltage and minimizes voltage drop. This protects your vehicle's electrical system, maximizes pump performance, and extends the pump's life. It is not an optional step for this level of pump; it's an essential part of the installation.

Performance Expectations & Real-World Use

After a correct installation with appropriate wiring, drivers can expect:

  • Consistent Fuel Pressure: Under full-throttle, high-load conditions (especially with forced induction or nitrous), fuel pressure remains stable and near the target pressure set by the regulator. This is fundamental for maintaining safe air/fuel ratios.
  • Elimination of Fuel Starvation: Engine hesitation, stuttering, or cutting out at high RPM due to insufficient fuel supply should be resolved, assuming other fuel system components (filter, lines, injectors) are also adequate.
  • Support for Higher Power Levels: The pump provides the volume headroom needed for significant power increases compared to stock or moderate upgrade pumps. It becomes an enabling component for future performance enhancements.
  • Smoother Operation under Load: Engines typically feel stronger and more responsive at high load points as the fuel supply constraint is lifted.

It's vital to remember that while the pump provides the volume, the pressure is controlled by the fuel pressure regulator (FPR). A rising-rate FPR (common in forced induction) helps maintain the correct pressure relative to intake manifold pressure (boost). Ensure your FPR is sized appropriately for the new pump's flow. Also, ensure your fuel filter(s) are clean and appropriate for the flow rate; a clogged filter can negate the pump's capabilities. Verify sufficient fuel line size (upgrading to -6AN may be necessary depending on power goals and vehicle setup). Upgrading only the pump without addressing potential bottlenecks downstream is incomplete.

Maintenance & Troubleshooting

Like all mechanical components, fuel pumps require attention and can experience issues:

  • Preventative Maintenance:

    • Fuel Filter Changes: Follow the manufacturer's recommendations, but increase frequency significantly if using E85. A partially clogged filter is a common cause of apparent "pump failure" as the pump struggles against the restriction. Consider replacing any in-tank pre-pump filters or inline filters at least annually on modified vehicles.
    • Clean Fuel: Dirty fuel or running the tank extremely low frequently introduces debris and sediment. This accelerates wear on the pump internals and clogs the filter sock/inlet. Keeping the tank reasonably full helps cool the pump.
    • Quality Fuel: Using reputable fuel sources minimizes contaminants. Consider fuel additives specifically designed for fuel system cleaning periodically, but avoid constant use of aggressive cleaners unless directed by a professional.

  • Troubleshooting Potential Issues:

    • Pump Doesn't Run:
      • Check fuse(s) (both factory and any added via wiring harness).
      • Check relay(s) (listen for click, swap with a known good one if possible, test operation).
      • Verify power and ground at the pump connector with a multimeter when ignition is turned "ON". Test actual voltage reaching the pump under load if possible. Check connections at the battery, relay, and pump.
      • Inspect all wiring for damage (chafed, melted, corroded).
    • Pump Runs, But No/Low Fuel Pressure:
      • Check for fuel leaks (underhood lines, injector o-rings, pump flange).
      • Replace fuel filter(s) (especially if pressure improves temporarily during prime then drops).
      • Verify fuel pressure regulator operation.
      • Check voltage at the pump terminals under load (engine cranking or running). Significant voltage drop indicates wiring issues.
      • Inspect the pump inlet filter sock for severe clogging (requires removing the pump assembly).
    • Pump Runs Excessively Noisy/Loud:
      • Verify adequate fuel level in the tank (pump can cavitate when low).
      • Check for damaged mounting points within the assembly causing vibration.
      • Ensure the pump isn't contacting the tank walls.
      • Listen for unusual grinding or whining – could indicate impending failure. Confirm wiring voltage is correct; low voltage can sometimes cause noise.
    • Intermittent Stalling/Power Loss:
      • Often electrical. Check for poor connections (corrosion, loose terminals) in the wiring harness, especially grounds. Confirm relay isn't intermittently failing.
      • Could be a failing pump motor starting to draw excessive current or seizing intermittently.
      • Check for fuel tank venting issues creating vacuum or vapor lock (less common on modern systems but possible).

Comparing to Alternatives: Why Choose the 340LPH?

Within the high-flow segment, several options exist:

  • AEM 380LPH/400LPH: Offer even higher flow for extreme horsepower applications (700+ WHP) or large-displacement engines. Generally require robust electrical upgrades. May be overkill for many builds needing 340LPH flow, adding unnecessary cost and electrical load.
  • 255LPH/290LPH Pumps (Various Brands): Sufficient for moderate upgrades (perhaps up to ~400WHP depending on application and safety margins). The AEM 340LPH provides a clear step up in flow capacity and headroom for more significant builds. It offers a noticeable performance margin over these without necessarily requiring the complexity or expense of the largest pumps.
  • External Belt-Driven Pumps: Necessary for extremely high horsepower (1000+ HP) but are complex, noisy, expensive, require dedicated mounting and plumbing, and often involve safety certifications. The AEM 340LPH, being an in-tank drop-in, is vastly simpler and quieter for its supported power range.
  • Dual Pump Setups: Using two smaller pumps (e.g., dual 255LPH) provides redundancy and high flow but requires custom hanger modifications, complex wiring/relays, and balancing. For builds where 340LPH is sufficient, a single AEM 340LPH is a simpler and often more cost-effective solution.

The AEM 340LPH strikes a compelling balance between substantial flow capacity, relative ease of installation (as a drop-in unit with wiring being the main upgrade need), widespread vehicle compatibility, proven reliability, and cost-effectiveness within the higher-horsepower bracket it serves. It addresses the limitations of smaller upgrade pumps while avoiding the complexity of extreme-flow solutions. Its brushless design in many variants adds to its reliability and longevity advantage.

Warranty and Support

AEM Electronics typically backs its fuel pumps with a limited warranty (often 1 or 2 years). Registration is usually required. Warranty generally covers defects in materials and workmanship under normal use. It does not cover failures due to improper installation, incorrect wiring/voltage, running the pump dry (fuel starvation), contamination damage (dirty fuel, water in fuel), use of non-compatible fuels beyond standard gasoline or specific E85 blends (verify pump specs), or physical damage. Retain proof of purchase and warranty registration. AEM's established presence and reputation in the performance parts market provide reliable support channels should issues arise that fall under warranty.

The Essential Component for Reliable Power

The AEM 340LPH fuel pump is far more than just an accessory; it is a foundational component for any serious engine performance upgrade requiring increased fuel delivery. Its ability to flow 340 liters per hour under pressure directly addresses the critical need for preventing fuel starvation and maintaining safe, reliable air/fuel ratios. Whether you're boosting a compact import, building a high-compression V8, or transitioning to E85, the 340LPH pump offers the robust flow capacity required. Remember, successful implementation hinges on three pillars: selecting the correct pump for your vehicle and power goals, executing a meticulous installation adhering to safety protocols (especially lock ring procedure and leak checks), and installing the mandatory dedicated high-current wiring harness. Neglecting the wiring is a recipe for disappointment and potential hazards. When properly integrated, the AEM 340LPH fuel pump becomes a dependable workhorse, ensuring your engine receives the vital fuel it demands to unleash its potential reliably and safely.

Back to blog