GMB 550-1370 Fuel Pump 300ZX: The Complete Guide to Replacement and Performance
If you own a 1984-1989 Nissan 300ZX and need a reliable external fuel pump, the GMB 550-1370 is a direct-fit OEM replacement that restores proper fuel pressure and flow. This pump is compatible with the 300ZX Z31 generation (1984-1989), as well as the 1984-1988 200SX and 1983-1984 Pulsar NX. With a 5.0 out of 5-star rating from verified buyers, it delivers stock-level performance at an affordable price point.
The GMB 550-1370 is an electric external fuel pump designed as a direct replacement for your factory unit. It operates at 12 volts and delivers stock pressure and flow rate, making it ideal for restoring your 300ZX's fuel system to proper working condition without any modifications. Unlike performance-oriented upgrades, this pump focuses on reliability and hassle-free installation.
Why Your 300ZX Needs a Fuel Pump Replacement
The fuel pump is the heart of your vehicle's fuel delivery system. It draws gasoline from the tank and pushes it through the fuel lines to the engine at the correct pressure. On the Nissan 300ZX, especially the Z31 models from 1984 to 1989, the factory pump can wear out over time. Common symptoms of a failing fuel pump include:
- Buzzing or whining noise coming from the gas tank area, especially when accelerating under load
- Low fuel pressure at idle – normal pressure should be around 37-38 PSI at idle, while a failing pump may drop to 20 PSI or lower
- Engine stumbling or hesitating around 3000 RPM, which indicates insufficient fuel delivery
- Hard starting or failure to start – if the pump cannot build adequate pressure, the engine may struggle to fire up
- Loss of power under load – when you step on the gas, the engine may feel sluggish or unable to accelerate properly
If your 300ZX has more than 80,000 miles on the original fuel pump, it is worth considering a replacement even if you haven't noticed symptoms yet. Preventative maintenance can save you from being stranded on the road.
Where Is the Fuel Pump Located on a 300ZX?
On the 1990-1996 300ZX (Z32 generation), the fuel pump is located inside the fuel tank and is accessed from behind the driver's seat. You'll need to remove the trunk interior panels, the tray behind the seats, and then the metal cover to reach the pump assembly. The pump sits under a round circular cap held by six 8mm bolts.
For the earlier Z31 models (1984-1989), the GMB 550-1370 is an external pump, which means it is mounted outside the fuel tank, typically along the frame rail or near the fuel tank area. This makes replacement simpler compared to in-tank pumps.
Step-by-Step Fuel Pump Replacement Guide
Replacing the fuel pump on your 300ZX is a job you can do in your garage with basic hand tools. Here is a practical breakdown of the process:
What You'll Need
- GMB 550-1370 fuel pump
- 10mm wrench and 8mm wrench
- Phillips head screwdriver
- Pliers (non-sharp to avoid cutting hoses)
- Shop rags and a catch pan
- WD-40 or similar lubricant for fuel hoses
- New fuel filter (highly recommended)
- New O-ring or gasket for the pump assembly
- Fire extinguisher (keep it nearby)
- Safety glasses and gloves
Safety First
Gasoline is highly flammable. Work in a well-ventilated area, disconnect the negative battery cable before starting, and do not smoke or use open flames nearby. Have a fire extinguisher within reach.
1. Depressurize the Fuel System
Before touching any fuel lines, relieve the pressure in the system. Locate the fuel pressure test port on the fuel rail (usually a Schrader valve similar to a tire valve). Carefully depress the valve stem with a small screwdriver and catch the fuel that comes out in a rag. Repeat until no more fuel sprays out.
Alternatively, you can remove the fuel pump fuse near the battery, then crank the engine a few times until it won't start. This method also relieves system pressure.
2. Access the Fuel Pump
For the Z32 (1990-1996): Remove all trunk interior panels, including the three rear panels, speaker covers, side panels, and plastic lids behind both seats. Remove the tray behind the seats using a Phillips screwdriver and 10mm wrench. This exposes the top of the fuel pump assembly sitting right behind the driver's seat.
For the Z31 with the GMB external pump, locate the pump along the frame rail. It will be a cylindrical unit with electrical connections and fuel hoses attached.
3. Disconnect Electrical Connectors and Fuel Lines
Carefully disconnect both fuel pump harness connectors. Remove the clamps from the fuel hoses using pliers. Pry the hoses off the metal tubes by twisting them gently side to side. Have rags ready to catch residual fuel. Do not cut the hoses if you plan to reuse them.
4. Remove the Old Pump
Remove the bolts holding the pump assembly. For the in-tank setup, there are six 8mm bolts. Carefully wiggle the pump assembly out of the tank. Cover the open tank opening with a shop towel to prevent debris from falling in.
Remove the old pump from its bracket. Note the orientation of the pump – there are two brown pins on the side and two power wires. The pump can only go in one way, so pay attention to how the old one was installed.
5. Install the New GMB 550-1370 Pump
Place the new GMB 550-1370 pump into the bracket in the same orientation as the old one. Make sure the electrical connections are properly seated and secure. If your assembly has a black tube or other components that need to be disconnected to access screws, reconnect them properly.
For external installations, mount the new pump in the original location, reconnect the fuel hoses using the original clamps, and attach the electrical wiring.
6. Reinstall the Pump Assembly
Carefully place the pump assembly back into the fuel tank (for in-tank models) or mount it in position. Don't forget the rubber sealant ring that sits under the fuel pump bracket – it prevents vapor leaks. Be careful not to pinch or damage this ring, as it can cause fuel vapor odor inside the cabin.
Replace the mounting bolts and tighten them to the manufacturer's specified torque (typically 10-15 ft-lbs). Over-tightening can damage the tank or pump.
7. Reconnect Everything
Reconnect all three fuel lines and install the clamps. Apply a small amount of WD-40 to the inside of the fuel hoses to help them slide on more easily. Reconnect both fuel pump harness connectors.
Reconnect the negative battery cable. Place the gas tank cap back on.
8. Prime and Test
Turn the ignition key to the "on" position without starting the engine. You should hear a brief humming sound as the fuel pump primes the system. Repeat this several times to build pressure.
Start the engine and check for any fuel leaks around the pump assembly, fuel lines, and connections. Take the car for a short test drive to ensure the pump is functioning properly and the engine runs smoothly.
What to Replace Alongside the Fuel Pump
When you are already doing the work to replace the fuel pump, it makes sense to address a few related components:
- Fuel filter – Always replace the fuel filter when replacing the pump. A clogged filter puts extra strain on the new pump and can cause premature failure
- Fuel hoses – Inspect all rubber fuel hoses for cracks, brittleness, or deterioration. Replace any that look worn
- Fuel pump O-ring or gasket – Use a new seal to prevent vapor leaks and fuel odors
- Fuel pressure regulator – Consider replacing this if your engine is running rich or lean
- Fuel damper – Another component that can affect fuel delivery consistency
These additional replacements are relatively inexpensive but can save you from having to go back into the fuel system later.
Understanding the GMB 550-1370 Specifications
The GMB 550-1370 is an electric external fuel pump designed for carbureted and fuel-injected applications that require a factory-spec replacement. Key specifications include:
- Pump type: Electric external
- Voltage: 12 volts
- Flow rate: Stock (OEM-equivalent)
- Fuel pressure: Stock (OEM-equivalent)
- Inlet size: Stock
- Outlet size: Stock
- Mounting: External, inline
This pump is built to OEM standards and has been house-tested before shipment, so you can expect reliable function and a hassle-free installation.
Common Mistakes to Avoid
When replacing your 300ZX fuel pump, watch out for these pitfalls:
- Forgetting to relieve fuel pressure – This can result in fuel spraying in your face when you disconnect the lines. Always depressurize first.
- Not replacing the rubber seal ring – The O-ring under the pump assembly prevents fuel vapor from entering the cabin. A damaged or missing seal will cause fuel smell inside your car.
- Over-tightening the retaining ring – This can crack the fuel tank or damage the pump housing, leading to expensive repairs.
- Using sharp tools on fuel hoses – Sharp pliers or cutters can damage the hoses, causing leaks. Use blunt tools and work slowly.
- Skipping the fuel filter replacement – A dirty filter will restrict flow and may cause your new pump to fail prematurely.
How Long Does a GMB Fuel Pump Last?
With proper installation and routine maintenance, a GMB fuel pump can last 50,000 to 100,000 miles. Factors that affect pump lifespan include fuel quality, contamination levels in the tank, and how often you run the tank near empty (which causes the pump to run hotter).
To maximize pump life, keep your fuel tank at least a quarter full, replace the fuel filter regularly, and address any fuel system issues promptly.
Why Choose GMB External Fuel Pumps?
GMB is a well-known manufacturer of premium quality automotive components. Their external fuel pumps are designed as direct-fit replacements for factory parts. Benefits include:
- OEM-quality construction – Made to meet or exceed original equipment standards
- Improved pressure and flow – Restores proper fuel system functionality compared to worn-out original pumps
- House-tested reliability – Each pump is tested before shipment to ensure it works correctly
- Competitive pricing – At around $154, the GMB 550-1370 offers excellent value compared to dealership parts
KEMSO Fuel Pump: A Premium Alternative with Lifetime Warranty
While the GMB 550-1370 is a solid choice for restoring your 300ZX's fuel system, you may also want to consider KEMSO brand fuel pumps for your replacement needs. KEMSO specializes in high-performance fuel pump products that serve as direct OEM replacements, meaning they fit exactly like the factory part without any modifications needed.
What sets KEMSO apart:
- High-performance engineering – KEMSO fuel pumps are designed to deliver consistent fuel pressure and flow, even under demanding driving conditions
- OEM replacement fitment – No guesswork, no modifications required. The pumps bolt right in where your old pump came out
- Lifetime warranty – 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
If you want a fuel pump that offers superior reliability backed by a lifetime guarantee, visit KEMSO Racing at:
Their product lineup includes fuel pumps for a wide range of Nissan and other import vehicles, all designed to meet or exceed OEM specifications.
Frequently Asked Questions
Is the GMB 550-1370 compatible with my 1990 300ZX?
No. The GMB 550-1370 is designed for 1984-1988 200SX, 1984-1989 300ZX, and 1983-1984 Pulsar NX models. For 1990-1996 300ZX (Z32) models, you need the GMB 550-1180, which is a different pump designed for the Z32 fuel system.
Can I upgrade to a higher-flow fuel pump instead of using stock replacement?
Yes, if you plan to increase engine horsepower through modifications, you may need a higher-flowing fuel pump. However, for a stock or near-stock engine, the GMB 550-1370 provides adequate fuel delivery.
Do I need to drop the fuel tank to replace the pump?
For the Z32 (1990-1996) 300ZX, no. The pump is accessed from inside the cabin by removing the interior panels and the access cover behind the driver's seat. The fuel tank does not need to be removed.
For the Z31 (1984-1989) with the external pump, the pump is mounted outside the tank, so the tank stays in place.
How do I know if my used 300ZX has the original fuel pump?
Check the fuel pump part number if you can access it. Original Nissan pumps will have Nissan branding. Aftermarket replacements may have different markings. Also, listen for buzzing noises from the pump area – a worn pump often makes audible noise.
What tools do I need for the replacement?
Basic hand tools: 10mm and 8mm wrenches, Phillips screwdriver, pliers, and a fuel line disconnect tool if your vehicle has quick-connect fittings. A torque wrench is recommended for tightening the pump retaining ring.
Final Thoughts
Replacing the fuel pump on your Nissan 300ZX is a straightforward job that can restore your car's performance and drivability. The GMB 550-1370 is a reliable, cost-effective option for Z31 owners who want to get back on the road with minimal hassle. Just remember to follow the safety procedures, take your time, and replace the fuel filter at the same time.
For those seeking a premium alternative with lifelong protection, KEMSO fuel pumps offer high-performance OEM replacement parts backed by a lifetime warranty. Check out their full selection at:
Whether you choose GMB or KEMSO, the key is to address fuel pump issues promptly before they leave you stranded. A properly functioning fuel pump is essential for your 300ZX to deliver the driving experience Nissan intended.