The AEM 340 Fuel Pump: Power, Performance, and Reliability for Demanding Engines

The AEM 340lph (liters per hour) high-flow in-tank electric fuel pump delivers substantial, reliable fuel volume at higher pressures for significantly modified engines requiring significantly more fuel than stock. It offers substantial performance gains over stock or mildly upgraded pumps, making it a cornerstone component for serious enthusiasts targeting high horsepower levels on gasoline with forced induction or large naturally aspirated engines.

AEM Performance Electronics has established a strong reputation in the automotive aftermarket for its fuel system components, intake systems, and engine management solutions. Their fuel pumps, particularly the high-flow models like the AEM 340, are frequently chosen by builders and tuners tackling demanding performance applications where fuel delivery is critical. This pump addresses the core need to supply sufficient fuel to support big power goals reliably.

Understanding the Purpose: Beyond Basic Fueling

Modern internal combustion engines require a precise amount of fuel delivered at the correct pressure for optimal combustion. As engine modifications increase horsepower output – especially through forced induction (turbochargers, superchargers) or significant increases in displacement and airflow – the demand for fuel skyrockets. Stock fuel pumps, designed for an engine's original output, quickly become overwhelmed. Insufficient fuel pressure or volume leads to lean conditions (not enough fuel relative to air), which is a primary cause of engine damage or catastrophic failure. The AEM 340 pump exists specifically to prevent this critical failure point on heavily modified vehicles.

Key Specifications and What They Mean

The designation "340" refers to the pump's approximate maximum flow rate: 340 liters per hour (lph), equivalent to roughly 90 US gallons per hour (GPH). This rating gives a relative comparison point against other pumps. However, several crucial specifications define its actual performance:

  1. Flow Rate: As stated, approximately 340 lph (90 GPH) at specific operating conditions. Flow rate decreases as pressure increases. This pump excels where high flow at higher pressures is needed.
  2. Pressure Rating: The AEM 340 is designed to operate within OEM-standard fuel pressure ranges common to electronic fuel injection systems, typically from around 40 PSI (base pressure) up to at least 75+ PSI. It maintains strong flow throughout this pressure range, which is vital when running boost-referenced regulators for forced induction engines.
  3. Voltage Requirement: It's a 12-volt DC pump, standard for automotive applications. However, its performance is significantly affected by voltage stability. High-performance applications demand excellent wiring to minimize voltage drop and ensure the pump receives the full electrical power it needs.
  4. Filter Sock: Equipped with a large area filter sock to prevent contaminants from entering the pump inlet, protecting both the pump and downstream fuel system components like injectors.
  5. Construction: Utilizes advanced materials and robust design principles, including brushless motor technology in some variants compared to the earlier brushed versions. This translates to reduced electrical noise (less radio interference) and potentially longer service life.

Installation Considerations: Not a Direct Drop-In for Everything

The AEM 340 is designed to fit into the fuel pump modules of many popular vehicles, particularly those commonly modified for high horsepower. However, it is absolutely NOT universally plug-and-play. Here’s what’s essential:

  1. Vehicle Application: Confirm with AEM's extensive application guides or reputable retailers that the specific AEM 340 part number is listed for your exact year, make, and model. Adapters or modifications to the fuel pump bucket (module) might be required even for listed vehicles.
  2. Pump Sleeve/Bucket: The pump often needs installation into the vehicle's existing fuel pump sleeve or bucket assembly. This requires careful disassembly of the stock module, removal of the old pump, and precise installation of the AEM 340 into the basket with appropriate strain reliefs and seals. Damaging the basket during removal or using incorrect seals can lead to fuel leaks or pump failure.
  3. Fuel Line Compatibility: Ensure the pump outlet's barb size matches the fuel line inside your pump module. Adapter fittings may be necessary to connect it securely to the factory or aftermarket fuel lines without leaks.
  4. Fuel Tank Access: This usually involves dropping the fuel tank or accessing the pump assembly from inside the car (e.g., under rear seats or trunk liner). This requires safety precautions – depressurize the fuel system, disconnect the battery, work in well-ventilated areas away from ignition sources, and have a fire extinguisher nearby.
  5. Sealing: Replacing the fuel pump assembly lid O-ring/gasket is MANDATORY. Reusing the old one almost guarantees a fuel leak under the pressure of the new pump. Only use the correct new gasket specified for your vehicle.

The Critical Role of Wiring and Voltage Supply

Under-delivering on electrical power to the AEM 340 is one of the most common causes of underperformance or premature failure. This is not a pump you can trust to run reliably on aging, undersized factory wiring, especially when supporting big power. Considerations are vital:

  1. Voltage Drop: Stock wiring harnesses can suffer significant voltage drop, especially over longer runs. When the pump receives less than 12 volts, its flow rate drops dramatically and its motor works harder, generating excessive heat and shortening its life. Measuring voltage at the pump's electrical connector under load (while running) is crucial. Readings consistently below 13.5V during high flow demand indicate a problem.
  2. Relay and Wiring Kits: Installing an aftermarket high-capacity fuel pump relay kit is HIGHLY recommended, often considered essential. This kit uses a heavy-duty relay triggered by the original pump control circuit but supplies power directly from the battery through appropriately sized (8-gauge or thicker) power and ground wires running directly to the pump in the tank. The factory wires then only carry the small current needed to activate the relay. This ensures minimal voltage drop and optimal pump operation.
  3. Connections: All connections must be clean, tight, properly crimped, and insulated. Solder connections with heat shrink tubing are superior for reliability. Corrosion or poor connections add resistance, increasing voltage drop.

Tuning Implications: Matching Components

Installing an AEM 340 does NOT guarantee more horsepower by itself. Its primary function is to supply fuel reliably. For it to achieve its purpose, the entire fuel system and engine management need upgrading:

  1. Fuel Injectors: To handle the increased volume and pressure delivered by the pump, significantly larger fuel injectors are almost always required. The pump delivers fuel to the injectors; the injectors must be sized correctly to flow the necessary fuel into the engine at your target horsepower level.
  2. Fuel Pressure Regulator (FPR): Forced induction applications absolutely require an adjustable boost-referenced FPR (rising rate regulator). This regulator increases fuel pressure in direct proportion to boost pressure, maintaining the critical fuel pressure differential across the injectors that the engine management expects. A stock FPR will cause severe fuel pressure drop under boost, leading to lean conditions. Even for high-power NA, an adjustable FPR helps tune base pressure.
  3. Engine Management Tuning: Any major change like a significantly larger fuel pump necessitates professional ECU tuning. The engine management system (ECU) must be recalibrated to account for the capabilities of the new pump, injectors, and regulator. This tuning adjusts injector pulse width, ignition timing, air/fuel ratios, and potentially other parameters to utilize the increased fuel flow safely and effectively, translating the fuel delivery into performance gains.

Typical Applications: Where the AEM 340 Shines

This pump is targeted squarely at the performance market. Common use cases include:

  1. 500-800+ Horsepower Applications: This is often considered the "sweet spot" range where the AEM 340 provides reliable headroom on gasoline for many platforms. The exact supported power level depends heavily on base fuel pressure, boost pressure, injector size, and whether a hanger upgrade is used.
  2. Forced Induction Upgrades: Turbo or supercharger kits that significantly increase airflow beyond what the stock fuel system can support. The AEM 340 provides the robust flow needed under boost pressure.
  3. Large Displacement Naturally Aspirated (NA) Engines: Big stroker motors, engine swaps (e.g., LS V8s into smaller cars), or aggressively cammed engines pulling in large amounts of air require much more fuel than stock systems deliver. The AEM 340 reliably meets this demand.
  4. Common Performance Platforms: Highly popular in modified Subaru WRX/STi, Mitsubishi Lancer Evolution, Ford Mustang, Chevrolet Camaro/Corvette, various Nissan/Infiniti (350Z, G35/G37, 370Z), BMW, and many other high-performance Japanese, American, and European vehicles.

Comparing the AEM 340 to Other Options

Understanding the landscape helps put the 340's role in context:

  1. Stock Pumps: Typically flow 80-180 lph, only suitable for mild or near-stock power levels. Will fail to meet the demands of significant power increases.
  2. "Mild" Upgrades (e.g., Walbro 255): Flowing ~255 lph, these are excellent choices for moderate power gains (e.g., up to 400-500whp, depending on pressure and other factors). They often offer easier drop-in fitment but may not have the headroom for more aggressive builds. Typically less expensive than the 340.
  3. The AEM 340 (340 lph): Sits between the mild upgrades and the very high-end pumps. Offers significantly more flow capacity than a Walbro 255, particularly at higher fuel pressures encountered under boost. Often requires attention to wiring but provides robust support for higher power levels. More expensive than mild upgrades.
  4. Higher Capacity Pumps (e.g., Walbro 450, DW 400, Bosch 044): These flow significantly more than the 340 (400+ lph). They are typically noisier, draw more current, generate more heat, often require extensive bucket/hanger modifications or external mounting, and are essential for very high horsepower goals (700whp+), E85 conversions, or large multi-pump systems. The AEM 340 offers a strong flow upgrade before needing this step for many platforms.

Troubleshooting Common AEM 340 Installation Issues

Even with careful installation, problems can arise:

  1. Whining Noise: While some inherent noise is normal for high-flow pumps, excessive whine is often caused by:
    • Fuel Starvation: Low fuel level (pump inlet uncovered), clogged filter sock, kinked feed line. Fix: Keep tank above 1/4 full, inspect sock/line.
    • Cavitation: Air entering the pump inlet due to leaks in the suction lines/connections or severe flow restrictions. Fix: Check all low-pressure side connections, inspect sock and pre-pump lines. Ensure pump is submerged.
    • Poor Mounting: Incorrect isolators or loose fitment allowing vibration transmission. Fix: Ensure correct installation with all factory rubber isolators/dampers.
    • Extreme Voltage Drop: Causes motor strain. Fix: Check and upgrade wiring.
  2. Lack of Fuel Pressure / Lean Conditions:
    • Severe Voltage Drop: Pump unable to spin fast enough. Fix: Measure voltage at pump connector under load; upgrade wiring/relay.
    • Clogged Filter / Sock: Restricted inlet. Fix: Inspect filter sock.
    • Leaks: Post-pump leaks (line, connection, FPR vacuum reference) preventing pressure build-up. Fix: Perform detailed leak check.
    • Failing FPR: Diaphragm rupture preventing pressure regulation. Fix: Test/replace FPR.
    • Plugged Fuel Filter: Post-pump external filter restriction. Fix: Replace filter.
    • Pump Failure: Less common, but possible if wiring was poor or starvation occurred. Fix: Check pump operation.
  3. Overheating / Intermittent Shutoff: Almost exclusively caused by poor wiring, severe voltage drop, or running the tank very low consistently. This strains the pump motor excessively.

Maximizing Performance and Longevity: Best Practices

Following these guidelines ensures you get the most from your investment:

  1. Quality Wiring & Relay Kit: This cannot be overstated. It protects the pump and ensures maximum flow capability.
  2. Fuel Tank Level: Avoid consistently running the fuel level very low (below 1/4 tank). This causes the pump to work harder to pick up fuel, increases heat, and accelerates wear. Keep the tank above 1/4 full whenever possible under high load conditions.
  3. Clean Fuel: While the pump sock catches larger debris, dirt or contaminants still cause wear over time. Use clean, quality fuel. Consider adding a high-quality pre-pump micron filter if contamination is suspected. Replace the filter sock if it becomes clogged or dirty.
  4. Professional Installation: If you lack experience, have the pump installed by a qualified professional familiar with performance fuel systems. Errors can be costly.
  5. Tuning: Ensure engine management tuning is completed after installing the pump, injectors, and regulator to properly utilize the new capabilities and ensure safe air/fuel ratios.
  6. Avoid Oversizing Unnecessarily: Installing a 340 for a mildly modified engine creates no benefit and can cause unnecessary wear and heat generation; a smaller pump is often sufficient and more economical.

Conclusion: The Right Choice for Significant Power Goals

The AEM 340 fuel pump is a highly capable workhorse engineered specifically for demanding automotive performance applications. It provides a substantial increase in flow capacity over stock or mild upgrade pumps, particularly at the elevated fuel pressures required by forced induction systems and large naturally aspirated engines. Its proven reliability and robust performance make it a cornerstone component for enthusiasts building vehicles targeting the 500-800+ wheel horsepower range on gasoline.

However, its successful integration demands meticulous attention to detail: verifying application fitment, performing a proper installation including potential bucket modifications and ALWAYS replacing the seal, addressing the electrical system comprehensively with a high-quality relay and wiring kit, and integrating it with appropriate larger injectors, an appropriate fuel pressure regulator, and crucially, professional engine management tuning. Neglecting any of these supporting elements drastically reduces its effectiveness or can lead to operational issues or even component failure.

If your power goals necessitate substantial fuel volume beyond what pumps like the Walbro 255 can reliably provide, and you are prepared to implement the necessary supporting upgrades and tuning, the AEM 340 is an excellent and widely trusted choice to form the foundation of your high-performance fuel system. It delivers the flow needed to make serious power safely, provided you set it up correctly.

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