The AEM 340 Fuel Pump: Powering High-Performance Engines with Reliability

For enthusiasts pushing their engines beyond stock limits, the AEM 340 fuel pump stands as a proven, high-flow solution essential for delivering the necessary gasoline or ethanol-blend fuels reliably and consistently. When horsepower targets climb significantly above factory specifications, the stock fuel pump simply cannot keep up. Upgrading to a dedicated high-volume fuel pump like the AEM 340 becomes a critical requirement to prevent dangerous lean conditions and unlock the full potential of modified engines. This component is specifically engineered to meet the demanding flow requirements of high-performance applications.

The core function of any fuel pump is straightforward: move fuel from the vehicle's tank to the engine's fuel injection system at the correct pressure and volume. Factory fuel pumps are precisely matched to the requirements of the stock engine configuration under all expected operating conditions. However, when modifications like turbocharging, supercharging, significant engine internal upgrades, or even major nitrous oxide systems are added, the engine's fuel consumption skyrockets. The stock pump quickly becomes inadequate, unable to supply the necessary volume of fuel, especially under high load and high RPM situations. This fuel deficit leads to a lean air/fuel mixture, excessive heat, and a high risk of catastrophic engine damage from pre-ignition or detonation.

The AEM 340 fuel pump directly addresses this critical limitation. Its defining characteristic is its significantly higher flow capacity compared to many stock and even some older aftermarket performance pumps. The "340" designation typically refers to its nominal flow rating of approximately 340 liters per hour (lph), measured at specific, standard industry test conditions like 13.5 volts and a defined fuel pressure (commonly 40 psi or 45 psi). This substantial flow rate – often around double or more what a typical stock pump delivers – provides the crucial fuel volume foundation needed to support engine outputs ranging from approximately 400 horsepower up to 600+ horsepower, depending on specific engine efficiency, fuel type, and system pressure. It acts as the indispensable lifeline supplying the fuel injectors with the sheer quantity of fuel demanded by highly tuned engines.

Compatibility and Installation are key practical considerations. The AEM 340 pump is designed to integrate seamlessly into a wide range of popular vehicles, particularly those frequently modified by the performance community. Common applications include various Honda/Acura models (Civic, Integra, S2000), Subaru WRX/STI, Mitsubishi Lancer Evolution, Mazda RX-7, Ford Mustang (especially Fox Body and SN95 with specific install kits), Nissan 240SX, Infiniti G35/G37, and many others. AEM provides detailed installation kits for specific vehicles, often including necessary brackets, pre-soldered wiring pigtails, strainers, and installation hardware. These kits transform the 340 pump into a direct, drop-in replacement unit for specific vehicle fuel pump assemblies. The pump itself is an in-tank design, meaning it is submerged in the fuel within the fuel tank for optimal cooling and quiet operation. Installation requires accessing the fuel pump hatch, usually located under the rear seat or in the trunk, and replacing the factory pump assembly. While straightforward for many experienced DIYers, it necessitates working with flammable gasoline, requiring strict safety precautions (working in well-ventilated areas, disconnecting battery) and proper handling procedures. Wiring upgrades are often essential; due to the pump's higher current draw compared to stock, installing a dedicated relay kit using appropriate gauge wiring directly from the battery is highly recommended to ensure stable voltage and prevent overheating the vehicle's factory wiring or fuel pump controller. Ensuring the fuel system, including the feed lines and filter, is clean prior to installation is also crucial for pump longevity.

Understanding Fuel System Requirements beyond the pump itself is vital. Installing a high-flow pump like the AEM 340 often necessitates reviewing and potentially upgrading other components within the fuel delivery system to achieve optimal performance and reliability:

1. Fuel Lines: Stock fuel feed lines might have insufficient internal diameter to handle the increased volume flow. Upgrading to larger diameter lines (commonly -6AN size) is recommended for high-horsepower applications to minimize flow restriction.
2. Fuel Filter: A high-flow fuel filter is necessary to prevent debris from damaging the pump or injectors without becoming a significant flow restriction point itself. Replacement intervals might need to be shorter due to the higher flow rates.
3. Fuel Pressure Regulator (FPR): Especially important for return-style fuel systems, a capable aftermarket adjustable fuel pressure regulator is required to maintain consistent rail pressure regardless of the increased flow volume. A rising rate regulator (RRFPR) might be needed for certain forced induction applications with high boost levels relative to base fuel pressure.
4. Fuel Injectors: The AEM 340 supplies the volume; properly sized fuel injectors capable of flowing sufficient fuel at the system's operating pressure are essential to actually deliver that fuel into the engine cylinders. The pump, injectors, and engine management must be correctly matched to the horsepower goal. Using a fuel injector sizing calculator based on target horsepower and fuel type is essential.
5. Engine Management: Precise control over fuel delivery requires compatible engine management. This could be an ECU upgrade (standalone or piggyback) or a programmable fuel pressure regulator, depending on the complexity and goals of the build. Simply adding a larger pump without proper tuning won't yield results and can cause issues.

Performance Characteristics and Key Features distinguish the AEM 340. Engineered specifically for performance use, this pump incorporates several design elements:

• High-Volume Brushless DC Motor: Utilizes an efficient brushless motor design known for durability and consistent performance compared to traditional brushed motors. This design contributes to longer service life and better thermal management.
• Multi-Stage Impeller Technology: The internal pumping mechanism is designed to move large volumes efficiently while generating sufficient pressure to meet modern fuel injection demands (typically maintaining pressures between 40-70+ psi throughout the operating range).
• Diesel & E85 Compatibility: Crucial for modern tuning, the AEM 340 pump is designed to handle both gasoline and ethanol-blended fuels like E85. E85 requires roughly 30-40% more volume flow than gasoline for the same horsepower output due to its lower energy density, making a pump like the 340 essential for high-power E85 builds. It also resists the corrosive effects of ethanol. While not certified for commercial diesel, its construction is robust enough for gasoline/diesel blends encountered in some racing fuels or biodiesel mixes. Always check specific manufacturer guidance.
• High Temperature Resilience: Designed to operate reliably within the hot environment of an in-tank fuel pump, even during extended high-load driving situations common in racing or spirited street use. Consistent performance under heat stress is critical.
• Longevity and Reliability: Built with performance-grade materials and components, the pump is engineered for sustained high-flow operation, offering dependable service in demanding applications when installed and maintained correctly. Its track record in various motorsports disciplines speaks to its robustness.

When an AEM 340 Fuel Pump is the Right Choice: This pump is ideally suited for specific performance scenarios:

• Moderate to High Horsepower Goals: When aiming for engine outputs typically in the 400-600+ horsepower range (on gasoline; figures decrease slightly for E85 due to its higher flow requirements). For significantly higher power levels (700-900+ hp), larger pumps like the AEM 400 might be more appropriate. For milder builds below 400hp, it might be overkill unless future upgrades are planned.
• Forced Induction Applications: Turbocharger and supercharger upgrades dramatically increase air intake, requiring proportional fuel increases. The AEM 340 is a standard upgrade for turbocharged Honda, Subaru, Mitsubishi, and Ford platforms, among others, running moderate boost levels.
• Nitrous Oxide Systems: Even small wet nitrous systems demand substantial extra fuel delivery precisely when activated. A high-flow pump like the 340 ensures adequate fuel is available on demand.
• High-Compression Naturally Aspirated Engines: Large displacement or high-revving naturally aspirated engines can also require flow rates exceeding stock pump capabilities.
• E85 Conversions: Converting to E85 fuel for its higher octane and potential power gains almost always necessitates a substantial fuel pump upgrade due to the significant increase in required fuel volume. The AEM 340 is a popular E85-ready solution. Verifying injector capacity and tuning are equally important.
• Replacing Weak or Failing Stock Pumps: On vehicles known for marginal stock fuel pumps or where the original pump has degraded (showing signs like lean conditions, hesitation, or failure), upgrading to a 340 provides significant headroom for performance and reliability. It's a robust replacement even if current mods don't require 340lph.

Recognizing the Need for an Upgrade: How does one know if their current pump is insufficient? Symptoms include:

• Engine Stumbling/Loss of Power Under Load: Especially at high RPM or wide-open throttle, indicating the pump cannot keep up with fuel demand.
• Lean Air/Fuel Ratio Readings: A wideband oxygen gauge consistently showing AFR values leaner than targeted under boost or high load is a critical warning sign.
• Long Crank Times: Especially when hot, as pump efficiency diminishes with heat.
• Whining/Groaning Noise Change: While performance pumps are generally louder, a significant change in pitch or volume from the tank might indicate strain or failure.
• Diagnostic Trouble Codes (DTCs): Codes related to low fuel pressure (P0190, P0191, P0192, P0193), fuel system performance, or lean conditions (P0171, P0174) can point towards fuel delivery issues, potentially the pump.
• Physical Pressure Measurement: The definitive test is using a fuel pressure gauge. Pressure dropping significantly below target specifications under load confirms pump inadequacy or system restriction. Verifying voltage at the pump connector under load is also important to rule out wiring issues.

Common Alternatives and Comparisons:

• Stock Replacements: Significantly cheaper but only suitable for unmodified engines.
• Smaller Aftermarket Pumps: Pumps rated around 190-255 lph (like Walbro 255 equivalents) are cost-effective for lower power levels (~250-400hp), potentially quieter, and draw less current. Good if the 340's capacity is unnecessary.
• AEM 340 vs. Walbro Equivalent: Historically, Walbro F90000267 (or equivalents like GSS342) was the main competitor. Both are excellent 340lph class pumps. AEM emphasizes its brushless motor technology. Selection often comes down to price, specific kit availability for the vehicle, and brand preference, as real-world performance is very similar.
• Larger Pumps (AEM 380, 400, 415): For extreme horsepower levels (700+ hp on gas, less on E85) or complex staged systems where headroom is critical. Draw more current, require larger wiring, and are noisier. Only necessary if the 340's proven capacity is insufficient for the build.
• Dual Pump Setups: Running two pumps (often two 255s or a combination) offers redundancy and can achieve flow rates exceeding a single 340. More complex installation (requiring special hat assembly, wiring, potentially plumbing) but offers ultimate capacity and some fault tolerance. Weight and complexity are trade-offs.

Maximizing Lifespan and Reliability:

• Clean Fuel System: A dirty tank or clogged filter forces the pump to work harder and can cause premature failure. Clean or replace the tank strainer sock during installation and install a new high-flow main fuel filter. Ensure the tank is clean before installing the new pump.
• Proper Wiring & Voltage: As stressed earlier, this is paramount. Use the appropriate gauge wire with a dedicated fuse and relay kit running directly from the battery. Low voltage increases amperage draw, generates heat, and drastically shortens pump life. Measure voltage at the pump under full load to confirm adequate supply (targeting 13.5V or more).
• Fuel Level Awareness: Avoid consistently running the tank extremely low. The fuel acts as a coolant for the pump motor. Submerging the pump frequently in very low fuel levels generates excessive heat and accelerates wear.
• Correct Fuel Type: Stick to fuels the pump is designed for (gasoline, E85 blends). Using pure methanol or diesel without manufacturer approval can damage seals and internals.
• Quality Installation Kit: Use a vehicle-specific installation kit designed for the AEM 340. Using makeshift brackets or incorrect strainers can lead to vibration issues, poor pickup, or fuel starvation. Ensuring the pump doesn't rub against anything in the tank assembly is crucial for long-term reliability.

Safety and Legal Considerations: Performance modifications carry inherent responsibilities:

• Flammability: Gasoline is highly volatile. Installation or fuel system work demands extreme caution – no sparks, open flames, excellent ventilation, fire extinguisher present. Relieve fuel system pressure before disconnecting lines.
• Emissions Regulations: Modifications affecting emissions compliance (often including fuel pump type depending on jurisdiction and specific engine management changes) may violate local laws. Understand the regulations applicable to your vehicle and location. AEM pumps designed for specific applications may sometimes be certified, but it's the installer's responsibility to comply with applicable regulations.
• Noise: High-flow fuel pumps produce a noticeable hum or whine, especially at key-on before starting. While often seen as normal in the performance community, it's a trade-off to be aware of. Ensure it's mounted securely to minimize potential resonance.
• Professional Installation: If unsure about any aspect of the installation, particularly wiring, seeking professional help is strongly advised. Incorrectly installed fuel systems pose fire and drivability risks. Many performance shops are very experienced with this common upgrade.

Long-Term Value: Investing in an AEM 340 fuel pump offers a critical solution for unlocking engine performance potential reliably. Its robust construction, high flow rate, compatibility with demanding fuels like E85, and established reputation make it a cornerstone upgrade for countless successful high-performance builds. When properly matched to the application, installed with correct supporting components and wiring, and maintained, it provides years of dependable service, delivering the essential fuel volume required to make serious power safely. It represents a fundamental step in building a fuel system capable of supporting significant engine modifications. Choosing this component signifies a commitment to building capable power while prioritizing engine protection through consistent fuel delivery. It’s more than just a pump; it’s an essential element enabling reliable performance.