AEM 340 Fuel Pump: The Ultimate Guide to Performance and Reliability

If you are looking for a fuel pump that can handle high horsepower applications while maintaining consistent fuel pressure, the AEM 340 fuel pump is one of the most reliable choices on the market. This electric in-tank pump is designed to support up to 340 liters per hour of flow, making it a go-to option for turbocharged, supercharged, and high-performance naturally aspirated engines. It works with both gasoline and E85 ethanol blends, and its compact design fits many stock fuel pump hangers without major modifications. In this guide, you will learn about its specifications, installation, benefits, common issues, and how it compares to other fuel pumps, all based on real-world experience and technical facts.

What Is the AEM 340 Fuel Pump and Why It Matters

The AEM 340 is a high-flow fuel pump manufactured by AEM Electronics, a company known for performance engine components. It is a direct replacement for many factory fuel pumps but offers significantly higher flow rates. For example, a stock fuel pump on a 2005 Subaru WRX flows around 200 liters per hour, while the AEM 340 flows 340 liters per hour at 43 PSI. This extra capacity ensures that your engine gets enough fuel under heavy load, preventing lean conditions that can cause detonation and engine damage.

The pump uses a turbine-style impeller, which is quieter and more efficient than older vane-style pumps. It is also compatible with ethanol fuels, which is critical because E85 requires about 30% more fuel flow than gasoline. Without a pump like the AEM 340, tuning for E85 can quickly exceed the limits of a stock unit.

Key Specifications of the AEM 340 Fuel Pump

Understanding the numbers helps you decide if this pump fits your project. Here are the most important details:

1. Flow Rate: 340 liters per hour (LPH) at 43 PSI (3 bar). At higher pressures, such as 58 PSI (4 bar), flow drops to around 280 LPH. This is still enough for engines producing up to 700 wheel horsepower on gasoline, or around 550 wheel horsepower on E85, depending on the injectors and fuel system setup.

2. Voltage Rating: It is designed for 12-volt systems. However, like many high-flow pumps, it flows more at higher voltage. At 13.5 volts, you can expect slightly more flow, but the pump is built to handle the typical automotive electrical system.

3. Current Draw: At 43 PSI and 12 volts, the pump draws about 8 to 10 amps. This is within the range of most factory fuel pump wiring, but for safety, especially if you upgrade to a larger pump, consider upgrading the wiring and relay to handle continuous current.

4. Fuel Compatibility: The AEM 340 works with gasoline, ethanol blends up to E85, and methanol blends up to M10. It should not be used with diesel or heavy biofuels without checking with the manufacturer.

5. Diameter and Height: The pump is 1.5 inches in diameter and 6.25 inches long. This size is close to many OEM pumps, so it fits in most in-tank modules. However, some newer vehicles with plastic tanks or specific modules may require minor modifications or an adapter kit.

6. Inlet and Outlet: The inlet uses a standard 5/16-inch barb or can be fitted with a push-on hose. The outlet is 3/8-inch NPT or can be adapted to AN fittings for braided lines.

Benefits of Using an AEM 340 Fuel Pump

Switching to an AEM 340 brings several practical benefits that matter for daily driving and track use.

First, consistent fuel pressure under high boost is the most important advantage. When you step on the throttle and the turbo spools, fuel demand spikes. A weak pump cannot keep up, pressure drops, and the engine runs lean. The AEM 340 maintains pressure up to its flow limit, which gives the tuner confidence to add more boost or timing.

Second, E85 compatibility is a huge plus for anyone tuning for ethanol. Many stock pumps cannot handle ethanol's corrosive properties over time, and even if they physically survive, they cannot flow enough. The AEM 340 is built with ethanol-resistant materials, including a special commutator and brushes.

Third, quiet operation is a common point of praise. Turbine pumps are inherently quieter than gear or vane pumps. Some owners report that the AEM 340 is barely audible inside the cabin, even at full load. This is not true for all high-flow pumps, so it is a real selling point.

Fourth, simple installation for most vehicles. Because the pump is close in size to OEM units, you can often drop it into the factory hanger without cutting wires or brackets. For popular platforms like the Subaru WRX, Mazda RX-7, Nissan 240SX, and BMW E36, many aftermarket retailers sell plug-and-play kits.

Fifth, long-term durability when maintained properly. AEM claims a service life of over 10,000 hours, which translates to many years of normal use. Of course, running the pump dry or using contaminated fuel can shorten its life, but under normal conditions, it holds up well.

How to Install the AEM 340 Fuel Pump Correctly

Installation is straightforward but requires careful attention to detail. Here is a step-by-step guide based on common installation methods.

Step 1: Safety First
Fuel is flammable, so disconnect the battery negative terminal. Let the engine cool completely. If the fuel tank is full, consider draining it to avoid spillage. Work in a well-ventilated area away from sparks or open flames.

Step 2: Access the Fuel Pump
Most vehicles require removing the rear seat or opening an access panel under the carpet. On some cars, you need to drop the fuel tank. Check your service manual. For example, on a 1998-2005 Subaru Impreza, you pull back the rear seat cushion and remove the round metal plate.

Step 3: Remove the Old Pump
Disconnect the electrical connector and fuel lines. Carefully pry the retaining ring or clips out. Lift the fuel pump assembly out of the tank. Be aware that some fuel will remain inside the module. Place it in a clean container.

Step 4: Compare the New Pump
Hold the AEM 340 next to your old pump. The physical size should be similar. If the old pump is shorter, you may need to use spacers or cut the mounting tube. Check the orientation of the inlet strainer – it should sit at the bottom of the fuel pump module.

Step 5: Install the New Pump
Remove the old pump from its bracket. Typically, it is held by rubber grommets or a plastic housing. Insert the AEM 340 into the same location. If the fit is tight, use a little soapy water to slide it in. Do not force it. Reconnect the fuel lines using the supplied fittings or your original ones. Use fuel-rated hose clamps.

Step 6: Wire the Pump
Most stock pumps use two wires – one positive, one negative. The AEM 340 uses the same polarity. If your vehicle has a fuel pump controller, you may need to bypass it or upgrade the wiring. For high-horsepower cars, install a separate relay and 12-gauge wire from the battery to the pump. This ensures the pump gets full voltage.

Step 7: Test Before Reassembly
Before putting everything back, reconnect the battery temporarily. Turn the key to the ON position (but do not start the engine). You should hear the pump prime for 2-3 seconds. If you hear it, check for fuel leaks at the connections. If not, check the wiring or fuse.

Step 8: Reassemble and Drive
Once the test is good, reinstall the fuel pump assembly into the tank. Put the retaining ring back and tighten it. Reconnect the fuel lines and electrical connector. Replace the access cover and seat. Start the engine and monitor fuel pressure with a gauge. It should match your specifications.

Common Issues and Solutions with the AEM 340

Even a high-quality pump can have problems if installed incorrectly or used outside its limits. Here are the most common issues reported by users and how to fix them.

Issue 1: Pump is Noisy
If the pump is louder than expected, it might be touching the bottom or side of the fuel pump module. This transmits vibration into the tank. Solution: Check the mounting orientation. Use rubber isolators if available. Also, ensure the fuel level is adequate. Running low on fuel can cause the pump to cavitate and make noise.

Issue 2: Fuel Pressure Drops Under Boost
This is usually a sign that the pump cannot supply enough flow at the pressure required by the fuel pressure regulator. For example, if you have a 1:1 rise rate regulator, at 20 PSI of boost on top of 43 PSI base pressure, the pump must deliver at 63 PSI. The AEM 340 flows about 280 LPH at that pressure. If your engine needs more than that, you need a larger pump. Solution: Check your injector duty cycle and fuel pressure. Upgrade to a 400 LPH pump if necessary.

Issue 3: Pump Stops Working After a Few Months
This can happen if the pump runs dry or if there is debris in the tank. The AEM 340 is sensitive to sediment because its clearances are tight. Solution: Always use a pre-filter strainer on the pump inlet. Replace the fuel filter in the engine bay regularly. If the pump fails, check the electrical connectors for corrosion. Use dielectric grease.

Issue 4: Car Runs Lean at High RPM
This might not be the pump itself. It could be the fuel pressure regulator, a clogged fuel filter, or a voltage drop to the pump. Solution: Measure voltage at the pump terminals while the car is idling. It should be close to battery voltage. If it is below 11 volts, the wiring is too small. Upgrade the wiring.

Issue 5: Pump Does Not Prime
If the pump does not make any noise when the key is turned, check the fuse first. Then check the relay. Many aftermarket pump installations require a rewire because the stock circuit cannot handle the current draw. Solution: Confirm the ground connection is solid. Use a test light to verify power at the pump connector.

Comparing AEM 340 to Other Fuel Pumps

To put the AEM 340 in perspective, here is how it stacks up against common alternatives.

Walbro 255 LPH Fuel Pump
The Walbro 255 is a classic upgrade for moderate horsepower (up to about 400 wheel horsepower on gasoline). It is cheaper and widely available. However, the AEM 340 flows about 30% more volume. On E85, the Walbro 255 becomes a bottleneck much sooner. The AEM 340 is also quieter and more efficient. If you plan to run E85 or exceed 450 wheel horsepower, the AEM 340 is the better choice.

AEM 400 LPH Fuel Pump
The AEM 400 is the big brother of the 340. It flows 400 LPH at 43 PSI and supports up to 900 wheel horsepower on gasoline. However, it is slightly larger physically, which can complicate installation in some tanks. It also draws more current (around 12-14 amps). For most street cars up to 700 horsepower, the 340 is sufficient. The 400 is for serious race cars.

Bosch 044 Fuel Pump
The Bosch 044 is an external pump, not in-tank. It is extremely durable and used in many race cars. But it is loud, requires external mounting, and is not E85 friendly without modifications. The AEM 340 is quieter, easier to install in-tank, and better suited for daily driving.

DeatschWerks DW300c Fuel Pump
The DW300c is a direct competitor to the AEM 340. It flows similarly (around 300-340 LPH) and is also E85 compatible. The main difference is installation ease. The DW300c is designed as a drop-in for many specific cars, while the AEM 340 is more universal. Both are good choices. The AEM 340 tends to be slightly cheaper.

Maintenance Tips for Long Life

To get the most out of your AEM 340 fuel pump, follow these simple maintenance practices.

Keep the tank at least 1/4 full. Running low on fuel regularly can overheat the pump because fuel cools and lubricates it. Lower fuel levels also allow sediment to be drawn into the pump.

Replace the fuel filter every 20,000 miles. A clogged filter after the pump increases backpressure, which forces the pump to work harder. This reduces flow and shortens pump life.

Use fresh fuel. Ethanol fuels absorb moisture over time. If your car sits for months, the fuel can degrade and cause corrosion. Add a fuel stabilizer if storing the vehicle.

Check for voltage drop. Over time, connectors can corrode. Measure voltage at the pump annually. If it drops below 13 volts while running, clean the connections or replace wires.

Listen for changes. If the pump suddenly becomes louder or starts whining, it may be failing. Prompt action can avoid getting stranded.

Real-World Performance and User Experiences

Many users report that the AEM 340 transformed their car's drivability. For example, on a 2006 Subaru STI running 25 PSI of boost on E85, the stock pump could not keep up above 6500 RPM. After installing the AEM 340, fuel pressure stayed stable to redline, and the dyno showed a gain of 20 wheel horsepower just from consistent fueling.

Another common scenario is on Mazda RX-7s with modified twin-turbo setups. The stock pump is often the weak link. The AEM 340 provides enough flow for up to 500 wheel horsepower on gasoline without needing a surge tank.

One important thing to note is that some users complain about the pump being slightly longer than the OEM unit in their specific car. For example, on some Honda Civics, the AEM 340 is too long to fit in the stock plastic bucket. In those cases, you can either modify the bucket, use a spacer, or buy a kit that includes a new bracket. This is rare but worth checking before purchasing.

Final Verdict

The AEM 340 fuel pump is a practical, high-quality upgrade for any car that needs more fuel flow. It is not the cheapest option, but the combination of high flow, E85 compatibility, quiet operation, and ease of installation makes it a strong contender for most performance builds up to 700 horsepower. If you are building a turbo car, planning to switch to E85, or just want a safety margin beyond the stock pump, the AEM 340 is a solid investment. Just remember to install it correctly, upgrade the wiring if needed, and keep the fuel system clean. That way, it will serve you reliably for years.