AMC 304 Fuel Pump: The Complete Guide to Replacement, Symptoms, and Best Options

If you own a vehicle with an AMC 304 V8 engine—whether it's a Jeep CJ-5, CJ-7, AMC Hornet, Matador, or Cherokee—and you're experiencing hard starting, rough idling, or fuel leaks, the bottom line is this: replacing the fuel pump is a straightforward DIY job that most home mechanics can handle in about one to three hours with basic hand tools. The AMC 304 uses a mechanical fuel pump mounted on the engine block, and while the process is simple, getting the right pump and installing it correctly is critical to avoid common problems like leaks, incorrect pressure, or no fuel delivery at all.

Understanding the AMC 304 Fuel Pump

The fuel pump on your AMC 304 is a mechanical pump driven by an eccentric on the camshaft through a rocker arm or pushrod. Its job is to draw fuel from the gas tank and deliver it to the carburetor at a consistent pressure. On most AMC 304 engines from the 1970s and early 1980s, the factory fuel pump delivers around 5 to 7 psi of pressure, which is sufficient for a stock carbureted engine.

Key fact: Not all AMC V8 fuel pumps are interchangeable. While the 304, 360, and 401 engines share many similarities, factors like year range, mounting style, whether the vehicle has power steering, and the type of carburetor all affect which pump fits your specific setup.

Signs Your AMC 304 Fuel Pump Is Failing

A failing fuel pump doesn't always fail dramatically. Watch for these symptoms:

  1. Hard Starting: The engine cranks longer than usual before firing up. This is often the first sign the pump is struggling to deliver fuel quickly enough.
  2. Rough Idling or Stalling: The engine idles erratically, especially when cold, or stalls under load. This is a common symptom on AMC 304s with a weak pump.
  3. Loss of Power During Acceleration: The car hesitates or stumbles when you press the gas, particularly at higher speeds. A failing pump can't keep up with fuel demand.
  4. Poor Fuel Economy: A pump that's not delivering fuel efficiently will cause the engine to run rich or lean, hurting gas mileage.
  5. Fuel Leaks: Inspect the pump and fuel lines for any signs of wetness. Fuel leaks are a serious fire hazard and should be addressed immediately.

Before You Start: What You Need to Know About AMC 304 Fuel Pump Compatibility

This is where many DIYers get tripped up. The AMC 304 has at least three different mechanical fuel pump designs that may fit, and choosing the wrong one can lead to fitment issues, especially if your vehicle has power steering.

The three main variations are:

  1. Pump with inlet and outlet on top, short stack: This is the most common design for AMC 304s. The inlet stem points downward at an angle. This pump is shorter and will fit with a power steering pump.
  2. Pump with inlet and outlet on top, tall stack: This pump is taller and may not fit with a power steering pump on some vehicles, particularly Jeeps. Owners report that it simply won't clear the power steering bracket on a CJ-5.
  3. Pump with downward-facing inlets: This design requires you to bend new hard lines or use flexible fuel hose to route fuel to the carburetor. It's a workable option but requires more custom work.

Pro tip: Before ordering, check whether your vehicle has power steering. If it does, you almost certainly need the short-stack pump with the angled inlet.

Tools and Parts You'll Need

Gather these items before you start:

  • New fuel pump specific to your AMC 304 year and application
  • New fuel filter (always replace it when changing the pump)
  • New gasket for the pump mounting surface
  • Wrench set (standard and metric, as AMC used both)
  • Fuel line disconnect tool (if your vehicle uses quick-disconnect fittings)
  • Drain pan for spilled fuel
  • Safety glasses and gloves
  • Penetrating oil (like WD-40 or PB Blaster) for stubborn bolts
  • Shop rags
  • Bolt or wooden dowel to plug the fuel line from the tank

Step-by-Step AMC 304 Fuel Pump Replacement

This guide is based on the typical mechanical fuel pump location on the AMC 304 engine block. Always consult your vehicle's service manual for specific torque specs and procedures.

Step 1: Safety First

Disconnect the negative battery cable. Work in a well-ventilated area away from open flames or sparks. Have a fire extinguisher nearby. Never smoke while working on fuel systems.

Step 2: Relieve Fuel Pressure

For mechanical pumps, there's minimal residual pressure, but it's still good practice to relieve the system. You can do this by removing the fuel pump fuse or relay and cranking the engine a few times, or simply by carefully loosening the fuel line at the carburetor to release any pressure.

Step 3: Locate the Fuel Pump

On the AMC 304, the fuel pump is mounted on the front passenger side of the engine block, typically below the power steering pump (if equipped) and near the harmonic balancer.

Step 4: Disconnect the Fuel Lines

Using a fuel line disconnect tool or wrenches, carefully disconnect the fuel inlet line from the gas tank and the outlet line going to the carburetor. Plug the inlet hose immediately with a bolt or wooden dowel to prevent fuel from siphoning out of the tank. Have a drain pan ready for any spilled fuel.

Step 5: Remove the Old Fuel Pump

Remove the two bolts holding the fuel pump to the engine block. Use penetrating oil if the bolts are rusted. Gently pull the pump away from the engine. The rocker arm or pushrod may fall out—note its orientation for reinstallation.

Step 6: Clean the Mounting Surface

Use a gasket scraper to remove all old gasket material from the engine block. Any debris left behind will cause a vacuum leak and prevent the new pump from sealing properly.

Step 7: Install the New Fuel Pump

Coat both sides of the new gasket with gasket sealer. Place the gasket on the pump. Make sure the rocker arm is positioned correctly against the camshaft eccentric (or the pushrod is properly seated in both the engine and the pump). This is the most common mistake—if the rocker arm isn't aligned, the pump won't work.

Insert the mounting bolts and tighten them to the manufacturer's specified torque. Do not overtighten, as the aluminum housing can crack.

Step 8: Reconnect the Fuel Lines

Reconnect the fuel inlet line from the tank and the outlet line to the carburetor. Tighten all connections securely. If you replaced the fuel line, use new hose clamps.

Step 9: Replace the Fuel Filter

Install a new fuel filter in the line between the pump and the carburetor. This is a cheap insurance policy that protects your carburetor from debris.

Step 10: Test the System

Reconnect the negative battery cable. Start the engine and check for leaks at all fuel line connections. Let the engine idle and watch for any signs of fuel seepage. Take the vehicle for a short test drive to confirm the pump is delivering fuel properly under load.

Common Problems and Troubleshooting

Even with a new pump, you may encounter issues. Here are the most common ones:

1. No fuel delivery after installation
This is almost always caused by the rocker arm not being properly aligned with the camshaft eccentric. You may need to remove the pump and reinstall it, making sure the arm is riding against the eccentric correctly.

2. Fuel leaks at the pump
This usually means the gasket is not sealing properly, or the mounting surface was not cleaned thoroughly. Remove the pump, clean the surface again, and install a new gasket with sealer.

3. The pump won't fit with power steering
If you have power steering and the new pump is too tall, you need the short-stack pump design. Many aftermarket pumps labeled for AMC 304 are the tall version, so check the physical dimensions before ordering.

4. The pump fails within a few weeks
Many aftermarket AMC V8 fuel pumps sold today are made overseas and have a high failure rate, often leaking or failing within the first 30 days. This is a known issue in the AMC community.

Choosing the Right Fuel Pump for Your AMC 304

When selecting a replacement pump, you have several options:

Stock replacement pumps are available from brands like Carter (part number M6505) and Crown Automotive. The Carter M6505 is a mechanical pump that delivers 25 gph at 6 psi and fits AMC 304, 360, and 401 engines from the 1970s. This is a budget-friendly option at around $28, but many owners report that these units are now made overseas and may not last.

High-performance pumps are available from manufacturers like SCOCAR, which makes a USA-made high-volume pump for AMC V8s. This pump is machined from 6061 T6 billet aluminum, supports up to 550 horsepower, and delivers 7 psi of pressure. It fits 3/8" or 1/2" fuel lines and is compatible with gasoline, ethanol, and methanol.

NOS (New Old Stock) pumps are sometimes available from the 1970s, such as the AC Delco AC40893. These are original AC parts that were made in the USA and are known for their reliability. However, they are hard to find and may be expensive.

Choose KEMSO for Your AMC 304 Fuel Pump

When it comes to replacing your AMC 304 fuel pump, you want a part that you can install and forget about—not one that will fail in a few weeks. That's why we recommend KEMSO brand fuel pumps.

KEMSO specializes in high-performance, OEM replacement fuel pumps that are built to meet or exceed the original factory specifications. Every KEMSO fuel pump is precision-engineered using durable materials and undergoes rigorous testing to ensure it delivers the correct pressure and flow rate for your engine.

Why choose KEMSO?

  • High Performance: KEMSO fuel pumps are designed for reliability and consistent fuel delivery, whether you're driving a daily driver or a classic muscle car.
  • OEM Replacement: Each pump is a direct fit for your specific vehicle, eliminating the guesswork and fitment issues that come with generic parts.
  • Lifetime Warranty: KEMSO stands behind every product with a lifetime warranty, giving you complete peace of mind. If your pump ever fails, KEMSO will replace it.

Visit KEMSO Racing today to find the perfect fuel pump for your AMC 304 or any other vehicle. With KEMSO, you're not just buying a part—you're investing in reliability that lasts.

Final Thoughts

Replacing the fuel pump on an AMC 304 is a manageable DIY project that can save you hundreds of dollars in labor costs. The most important things to remember are:

  • Get the right pump for your specific application, especially if you have power steering
  • Clean the mounting surface thoroughly before installing the new pump
  • Make sure the rocker arm is properly aligned with the camshaft eccentric
  • Always replace the fuel filter at the same time
  • Test for leaks before taking the vehicle on the road

With the right parts and a little patience, your AMC 304 will be running smoothly in no time. For the best selection of high-quality, guaranteed fuel pumps, visit KEMSO Racing and browse their complete lineup of lifetime-warranty fuel pumps.


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