GMB 550-1370 Fuel Pump 300ZX: The Complete Replacement Guide for Nissan 300ZX Owners

If you own a 1984-1989 Nissan 300ZX (Z31 generation) and need a reliable fuel pump replacement, the GMB 550-1370 fuel pump is a direct-fit, OEM-quality solution that will restore your fuel system to proper working condition. This external electric fuel pump is specifically designed for the 1984-1989 Nissan 300ZX, as well as the 1984-1988 200SX and 1983-1984 Pulsar NX. It provides stock pressure and flow rates, meaning you get exactly what your engine needs without any modifications. The pump is built to OEM standards, house-tested for reliability, and backed by GMB's reputation as a global OE supplier with over 50 years of experience. In short, if your 300ZX is experiencing fuel delivery issues, the GMB 550-1370 is a drop-in replacement that will get you back on the road quickly and safely.

Understanding the GMB 550-1370 Fuel Pump

The GMB 550-1370 is an electric external fuel pump designed for carbureted and early fuel-injected Nissan vehicles from the mid-1980s. Unlike modern in-tank pumps that sit inside the fuel tank, this external pump mounts outside the tank, typically along the frame rail or near the fuel tank area. This design was common on Z31-generation 300ZX models, which used an external fuel pump configuration.

Key Specifications

  • Fuel Pump Type: Electric external
  • Voltage: 12 volts DC
  • Flow Rate: Stock (matches original factory specifications)
  • Fuel Pressure: Stock (matches original factory specifications)
  • Inlet Size: Stock factory size
  • Outlet Size: Stock factory size
  • Gasket Included: No (you will need to reuse your existing gasket or purchase a new one separately)
  • Wiring Harness Included: No (reuse your factory wiring)
  • Mounting Bracket Included: No (reuse your factory bracket)

The pump is sold individually, so you will need to transfer your existing mounting hardware, electrical connectors, and fuel line fittings from your old pump to the new one.

Why Choose the GMB 550-1370 for Your 300ZX?

OEM-Quality Construction

GMB manufactures their fuel pumps using 99.90% pure copper internal wiring for superior electrical conductivity and consistent fuel pressure delivery. This is critical because inferior-quality pumps often use lower-grade wiring that can lead to voltage drops, inconsistent pressure, and eventual pump failure. The motors are built to meet original equipment manufacturer specifications for voltage, amperage, resistance, pressure, and volume.

High-Grade Aluminum Heat Dissipation Sleeve

The GMB 550-1370 features a 5052-grade aluminum alloy heat dissipation sleeve that wraps around the motor casing. Electric fuel pumps generate significant heat during operation, and this sleeve allows heat to dissipate quickly, preventing overheating and extending the pump's service life. Lower-quality pumps without this feature are more prone to burning out prematurely.

150-Micron Pre-Pump Filter

Every GMB fuel pump includes a 150-micron pre-pump filter (strainer) made from high-quality filter material without paper. This filter catches contaminants before they enter the pump, protecting the internal components from damage. Clogged filters are one of the leading causes of premature fuel pump failure, so having a quality strainer is essential for long-term reliability.

Vacuum-Formed Plastics (POM)

The pump assembly uses high-grade vacuum-formed plastics that resist cracking, warping, and deformation under heat. This same technology is used in manufacturing other automotive plastic components like intake manifolds and radiator tanks. Cheap plastic assemblies can warp when hot, putting stress on the pump and affecting fuel level floaters.

How to Know If Your 300ZX Needs a New Fuel Pump

Before you buy the GMB 550-1370, you need to confirm that your existing pump is actually failing. Here are the most common symptoms of a bad fuel pump on a Nissan 300ZX:

1. Engine Sputtering or Hesitation Under Load

If your engine sputters, stumbles, or hesitates when you accelerate, especially around 3000 RPM, the fuel pump may not be delivering enough pressure. This is a classic sign of a pump that is wearing out and cannot maintain proper flow under demand.

2. Low Fuel Pressure at Idle

A healthy Z31 300ZX should have around 37-38 PSI of fuel pressure at idle. If you check the pressure and it reads significantly lower, such as 20 PSI or less, the pump is failing and needs replacement.

3. Buzzing or Whining Noise from the Fuel Tank Area

When a fuel pump starts to fail, it often makes a loud buzzing or whining noise. On a 300ZX, you may hear this noise coming from behind the driver's seat or from under the rear of the car. A healthy pump should operate quietly, so any unusual noise is a red flag.

4. Engine Cranks But Won't Start

If the engine cranks normally but does not start, and you have confirmed that there is spark, the fuel pump may not be delivering fuel. You can check by listening for the pump to prime when you turn the key to the "ON" position. If you do not hear a brief humming sound, the pump may be dead.

5. Car Dies Shortly After Starting

Sometimes a failing pump will allow the car to start but then die after a few seconds. This happens because the pump cannot maintain pressure once the engine is running and demanding fuel.

Step-by-Step Installation Guide for the GMB 550-1370

Replacing the fuel pump on a 1984-1989 Nissan 300ZX is a job you can do at home with basic hand tools. However, because you are working with gasoline, safety must be your top priority.

Safety Precautions

Work in a well-ventilated area and disconnect the negative battery cable before starting. Have a fire extinguisher nearby. Gasoline is highly flammable, and even a small spark can cause a fire. Do not smoke or have any open flames near the work area.

Tools You Will Need

  • 10mm wrench
  • 8mm wrench
  • Phillips screwdriver
  • Pliers (blunt-tipped, not sharp)
  • Fuel line disconnect tool (if needed)
  • Rags or shop towels
  • Catch pan for fuel
  • Jack and jack stands (if you need to raise the vehicle)
  • Torque wrench (10-15 ft-lbs for retaining ring)

Step 1: Relieve Fuel System Pressure

This is critical. Locate the fuel pressure test port on the fuel rail, which is usually a Schrader valve similar to a tire valve. Carefully depress the valve stem with a small screwdriver and catch the fuel in a rag. Repeat until no more fuel comes out. On some models, you can also remove the fuel pump fuse and crank the engine until it stops running to relieve pressure.

Step 2: Access the Fuel Pump

The fuel pump on the Z31 300ZX is accessed from inside the car. Remove the rear seats and the access panel covering the fuel tank sending unit. On some models, you may need to remove interior trunk panels first.

Step 3: Disconnect Electrical Connectors and Fuel Lines

Carefully disconnect the electrical connector(s) from the fuel pump sending unit. Then, disconnect the fuel lines. Be prepared for some residual fuel to spill out. Use a fuel line disconnect tool if the fittings are tight. Take pictures before disconnecting anything so you know how to reassemble it correctly.

Step 4: Remove the Sending Unit Assembly

The sending unit is secured to the fuel tank with a retaining ring or bolts. Carefully loosen the retaining ring using a special tool if recommended, or remove the bolts. Slowly lift the sending unit out of the tank, being careful not to bend the float arm for the fuel level sensor.

Step 5: Remove the Old Fuel Pump

Once the sending unit is out, you can access the fuel pump itself. The pump is held in place by a bracket or clip. Carefully remove the bracket and disconnect the pump from the sending unit wiring harness. Note the orientation of the pump because you will need to install the new one the same way. Also, detach the old fuel filter sock.

Step 6: Install the New GMB 550-1370

Attach the new fuel filter sock (strainer) to the inlet of the new pump. Install the new pump into the sending unit, making sure it is securely mounted and the wiring is properly connected. Use new rubber isolators if the old ones are cracked or deteriorated. The GMB 550-1370 should fit directly into the factory bracket without any modification.

Step 7: Reinstall the Sending Unit

Carefully lower the sending unit back into the fuel tank, making sure the float arm is not bent or obstructed. Secure the sending unit with the retaining ring or bolts. Use a new gasket or O-ring to prevent fuel leaks and vapor odors. A GMB fuel pump tank seal is available separately for this purpose. Tighten the retaining ring or bolts to 10-15 ft-lbs using a torque wrench.

Step 8: Reconnect Fuel Lines and Electrical Connectors

Reconnect the fuel lines and electrical connectors. Double-check that everything is properly seated and secured. Apply a small amount of silicone grease to the O-rings to enhance sealing.

Step 9: Prime the Fuel System

Turn the ignition key to the "ON" position (without starting the engine) for a few seconds. This allows the fuel pump to prime the system. Repeat this process several times. You should hear a brief humming sound from the pump.

Step 10: Start the Engine and Check for Leaks

Start the engine and check for any fuel leaks around the sending unit, fuel lines, and connections. If you find any leaks, immediately shut off the engine and address the problem.

Step 11: Test Drive

Take the car for a test drive to ensure the pump is functioning properly and the engine is running smoothly.

Important Considerations for Your Replacement

Replace the Fuel Filter

Always replace the fuel filter when replacing the fuel pump. A clogged filter puts extra strain on the new pump and can cause it to fail prematurely. This is cheap insurance that will extend the life of your new GMB pump.

Inspect Fuel Hoses

While you are in there, inspect all fuel hoses. Replace any that are cracked, brittle, or show signs of deterioration. Old hoses can leak or collapse under pressure.

Check the Fuel Tank Condition

This is a good opportunity to inspect the inside of the fuel tank for rust or debris. If you find excessive rust, consider having the tank cleaned or replaced. Contaminants in the tank are one of the leading causes of fuel pump failure.

Keep the Tank at Least Half Full

To maximize the life of your new fuel pump, try to keep your gas tank at least half full. The gasoline helps cool the pump, and running low on fuel frequently can cause the pump to overheat.

Why Choose KEMSO Fuel Pump for Your 300ZX

While the GMB 550-1370 is a solid OEM replacement option, we highly recommend considering KEMSO brand fuel pumps for your Nissan 300ZX. KEMSO fuel pumps are designed as high-performance OEM replacement parts that meet or exceed factory specifications. Every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind that your investment is protected for as long as you own your vehicle.

KEMSO understands that your 300ZX deserves quality components that deliver reliable performance. Their fuel pumps are precision-engineered to provide consistent fuel pressure and flow, ensuring your engine runs smoothly under all driving conditions. Whether you are restoring a classic Z31 to its original glory or building a performance-focused machine, KEMSO has the right fuel pump for your needs.

Visit KEMSO Racing today to browse their full selection of fuel pumps and accessories: https://www.kemsoracing.com/

Frequently Asked Questions About the GMB 550-1370

Is the GMB 550-1370 compatible with my 1986 Nissan 300ZX?

Yes, the GMB 550-1370 is listed as compatible with the 1984-1989 Nissan 300ZX, which includes the 1986 model year. It is an external fuel pump designed for these vehicles.

Does the GMB 550-1370 come with a gasket?

No, the pump is sold individually without a gasket. You will need to purchase a separate gasket or O-ring for the fuel tank sending unit. GMB offers a fuel pump tank seal for 1990-1996 300ZX models, but for the Z31 generation, you should check your existing gasket and replace it if necessary.

Can I use the GMB 550-1370 for a high-performance or turbocharged 300ZX?

The GMB 550-1370 is designed for stock flow and pressure. If you have modified your engine for more horsepower, you may need a higher-flowing aftermarket fuel pump. For stock or mildly modified engines, this pump is perfectly adequate.

How long does the GMB 550-1370 typically last?

With proper installation and maintenance, including regular fuel filter changes, a GMB fuel pump can last 80,000 to 100,000 miles or more. Preventative maintenance is key to maximizing pump life.

Do I need to drop the fuel tank to replace the pump on a 1985 300ZX?

On the Z31 300ZX, the fuel pump is accessed from inside the car by removing the rear seats and access panel. You do not need to drop the fuel tank for pump replacement. However, on some early models, the procedure may vary, so consult your service manual.

Final Thoughts

The GMB 550-1370 fuel pump is a reliable, direct-fit replacement for your 1984-1989 Nissan 300ZX. It is built to OEM standards with high-quality materials, including pure copper wiring, an aluminum heat dissipation sleeve, and a 150-micron pre-pump filter. Installing this pump yourself is achievable with basic tools and careful attention to safety procedures.

Remember to replace your fuel filter at the same time, inspect your fuel hoses and tank condition, and use a new gasket for the sending unit. These simple steps will ensure your new pump delivers years of trouble-free service.

For those who want the added security of a lifetime warranty, KEMSO fuel pumps are an excellent alternative. Visit KEMSO Racing to explore their complete line of high-performance fuel pumps designed for your 300ZX and other vehicles. With KEMSO, you get quality, performance, and peace of mind backed by a lifetime warranty.


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