1990 Nissan 300ZX Fuel Pump Relay Location: The Complete Guide to Finding and Fixing It

If your 1990 Nissan 300ZX cranks but won't start, and you don't hear the fuel pump prime when you turn the key to the ON position, the fuel pump relay is likely the culprit. The fuel pump relay on a 1990 Nissan 300ZX is located behind the left-hand side (driver's side) kick panel, inside the passenger compartment. You need to remove the interior trim panel covering the fuse box area to access it. The relay is typically a green relay mounted on the metal bracket near the fuse panel . This is the most common location for both the naturally aspirated (NA) and twin-turbo (TT) models.

Understanding the Fuel Pump Relay System

The fuel pump relay is an electrical switch that controls power to the fuel pump. When you turn the ignition key to the ON position, the Engine Control Module (ECM) triggers the relay, which then sends battery voltage to the fuel pump. The pump runs for a few seconds to pressurize the fuel system before the engine starts, then continues running once the engine is running .

The 1990 300ZX has a more complex fuel pump control system than many other cars. It includes not just the relay but also a Fuel Pump Control Unit (FPCU) that regulates fuel pump speed based on engine demand . The relay itself is a simple on-off switch, while the control unit modulates the pump's voltage for variable speed operation.

Exact Location of the Fuel Pump Relay

Driver's Side Kick Panel

The primary location for the fuel pump relay is behind the driver's side kick panel. Here's how to find it:

  1. Open the driver's door and look at the side panel to the left of the steering wheel, near the floor.
  2. Remove the plastic kick panel trim. It is held in place by clips or screws. You may need a trim removal tool or a flathead screwdriver to gently pry it off.
  3. Behind this panel, you will see the fuse box and several relays mounted on a metal bracket.
  4. The fuel pump relay is a green relay located directly below the hood release cable, on the edge of the metal bracket near the fuse panel .

Multiple sources confirm this location. The factory service manual lists the fuel pump relay as being "Behind LH Side Of Instrument Panel" . This is consistent across the 1990-1996 model years.

Alternative Location: Behind the Passenger Seat

Some owners report that the fuel pump relay can also be found behind the passenger seat, next to the fuel pump control unit. However, this is actually the room lamp relay, not the fuel pump relay. The factory service manual clearly distinguishes between these two components . The fuel pump control unit is located under the driver's seat, while the relay itself is in the kick panel.

What the Relay Looks Like

The fuel pump relay on the 1990 300ZX is a standard automotive relay. It is typically green in color, though it may be black or gray depending on the manufacturer. It has four or five pins and plugs into a socket on the relay bracket. The relay is approximately 1 inch square and about 1.5 inches tall.

How to Test the Fuel Pump Relay

Before replacing the relay, you should test it to confirm it is faulty. A bad relay can cause the fuel pump to not run at all, or it may cause intermittent operation.

Visual Inspection

Start with a visual inspection. Look for signs of corrosion, melted plastic, or burnt contacts on the relay. If the relay looks damaged, replace it immediately.

Click Test

With the key in the OFF position, have a helper turn the key to the ON position while you listen near the relay. You should hear a distinct click sound as the relay engages. If you hear the click but the fuel pump doesn't run, the relay may be working but the pump or wiring could be faulty.

Multimeter Test

Use a digital multimeter to test the relay:

  1. Remove the relay from its socket.
  2. Set the multimeter to measure resistance (ohms).
  3. Check the resistance between the coil terminals (usually pins 85 and 86). You should see a reading between 50 and 120 ohms. If the reading is infinite (open circuit), the relay coil is bad.
  4. Check the switch terminals (usually pins 30 and 87). With the relay not energized, there should be infinite resistance (open circuit).
  5. Apply 12 volts to the coil terminals (pins 85 and 86). You should hear a click. Now check the switch terminals again. They should show near-zero resistance (closed circuit).

Voltage Test at the Relay Socket

You can also test the circuit at the relay socket:

  1. With the relay removed, turn the ignition key to the ON position.
  2. Use a multimeter to check for 12 volts at the power supply terminal (usually pin 30).
  3. Check for ground at the coil terminal (usually pin 85).
  4. Have a helper turn the key to the START position and check for 12 volts at the trigger terminal (usually pin 86) .

If you have power at the relay but the fuel pump still doesn't run, the problem may be in the wiring between the relay and the pump, or the pump itself may be faulty.

How to Replace the Fuel Pump Relay

Replacing the fuel pump relay is a straightforward process that most DIYers can handle in about 15 minutes.

Step 1: Gather Your Tools

You will need:

  • A replacement fuel pump relay (available at most auto parts stores)
  • A trim removal tool or flathead screwdriver
  • A flashlight

Step 2: Access the Relay

Remove the driver's side kick panel as described earlier. You may also need to remove the lower dashboard trim panel to get better access to the relay bracket.

Step 3: Remove the Old Relay

The relay simply pulls straight out of its socket. Grip the relay firmly and pull upward. It may require a bit of force, but it should come out without any tools.

Step 4: Install the New Relay

Push the new relay straight into the socket until it is fully seated. Make sure it clicks into place. The relay is keyed, so it can only be installed in one orientation.

Step 5: Test the System

Turn the ignition key to the ON position. You should hear the fuel pump prime for about 2 seconds. If you don't hear the pump, check the fuel pump fuse in the fuse panel.

Step 6: Reinstall the Trim Panel

Snap the kick panel back into place. Make sure all clips are properly engaged.

Other Related Components

Fuel Pump Fuse

The fuel pump fuse is located in the fuse panel behind the driver's side kick panel, near the relay. Check this fuse before replacing the relay. A blown fuse will prevent the fuel pump from running.

Fuel Pump Control Unit

The Fuel Pump Control Unit (FPCU) is a separate component that controls the fuel pump speed. It is located under the driver's seat, mounted on the floor pan under a metal shield . To access it:

  1. Remove the driver's seat (four 10mm bolts).
  2. Remove the metal shield secured by Phillips-head screws.
  3. The FPCU is a small black box with electrical connectors.

A faulty FPCU can cause the fuel pump to run at full speed constantly or not run at all. It is a known failure point on the Z32 300ZX.

Fuel Pump

The fuel pump itself is located inside the fuel tank. On the 1990 300ZX, you access it from inside the trunk. Remove the carpet on the hump between the trunk and the rear seats. There is a circular access panel on top of the fuel tank. Remove this panel to access the fuel pump assembly .

Common Symptoms of a Bad Fuel Pump Relay

Recognizing the symptoms of a bad fuel pump relay can save you time and frustration:

Engine cranks but won't start: This is the most common symptom. The starter turns the engine over, but the engine never fires because no fuel is being delivered.

No fuel pump prime sound: When you turn the key to the ON position, you should hear a brief whirring sound from the fuel pump. If you don't hear this sound, the relay or pump may be faulty.

Intermittent starting: The car starts sometimes but not others. This can indicate a failing relay that works intermittently.

Engine stalls while driving: If the relay fails while the engine is running, the fuel pump will stop, and the engine will stall immediately. This is a safety concern and should be addressed promptly.

Check engine light: The ECM may set a diagnostic trouble code (DTC) related to fuel pump circuit failure. You can check for codes using the self-diagnostic feature on the 1990 300ZX.

Diagnostic Tips for No-Start Conditions

If your 1990 300ZX won't start, follow this systematic approach:

Check for Spark

Remove a spark plug, reconnect it to the spark plug wire, ground the plug against the engine block, and have a helper crank the engine. You should see a strong blue spark. If you have spark, the ignition system is likely working .

Check for Fuel Pressure

Use a fuel pressure gauge connected to the Schrader valve on the fuel rail. The 1990 300ZX should have 43 psi of fuel pressure . If you have no pressure, the fuel pump is not running.

Listen for the Fuel Pump

With the key in the ON position, listen near the fuel tank for the pump priming sound. If you don't hear anything, check the relay and fuse first.

Check the Fuel Pump Relay

As described above, locate and test the relay behind the driver's side kick panel.

Check the Fuel Pump Control Unit

If the relay tests good but the pump still doesn't run, check the FPCU under the driver's seat. Use a multimeter to check for power and ground at the FPCU connector .

Check the Fuel Pump Itself

If all upstream components test good, the pump itself may be faulty. You can test the pump by applying 12 volts directly to the pump connector to see if it runs.

Why the Fuel Pump Relay Matters

The fuel pump relay is a critical safety component. It ensures that the fuel pump only runs when the engine is running or when the key is in the ON position. If the relay fails in the closed position, the fuel pump could run continuously, even with the engine off. This can drain the battery and create a fire hazard.

Conversely, if the relay fails in the open position, the fuel pump will not run at all, and the engine will not start. This is the more common failure mode.

Variations Between Models

Naturally Aspirated (NA) vs. Twin-Turbo (TT)

The fuel pump relay location is the same for both the NA and TT models. The relay is behind the driver's side kick panel for both versions .

However, the TT model has additional components in the fuel system, including a wastegate control valve and a boost sensor that can affect fuel delivery indirectly . The fuel pump system itself is similar between the two versions.

1990 vs. Later Years

For the 1990-1996 300ZX (Z32 generation), the fuel pump relay location is consistent across all model years. The relay is always behind the driver's side kick panel .

For the earlier Z31 generation (1984-1989), the fuel pump relay may be in a different location, such as in the engine bay fuse box or behind the passenger side kick panel.

Preventive Maintenance

The fuel pump relay is a wear item that can fail over time. Here are some tips to prevent unexpected failures:

Replace the relay proactively: If your 300ZX is over 20 years old, consider replacing the relay as preventive maintenance. It's a cheap part that can leave you stranded if it fails.

Keep a spare relay in the glove box: The relay is small and inexpensive. Having a spare can save you a tow truck call if the relay fails while you're on the road.

Check the relay socket for corrosion: Moisture can get behind the kick panel and cause corrosion on the relay terminals. Clean the socket with contact cleaner if you see any corrosion.

Inspect the wiring: Look for chafed or damaged wires in the relay harness. Vibration can cause wires to wear through and short out.

When to Call a Professional

While replacing the fuel pump relay is a simple DIY job, some situations require professional help:

  • You smell fuel or see smoke near the relay area.
  • The relay socket is melted or damaged.
  • The wiring harness is damaged and requires repair.
  • You have tested the relay and pump but still have no fuel delivery.
  • You are not comfortable working with electrical systems.

If you encounter any of these situations, take your 300ZX to a qualified mechanic who specializes in Nissan vehicles.

Upgrade Your Fuel System with KEMSO

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The KEMSO 340 high-pressure fuel pump is capable of supporting applications up to 700-800 horsepower, making it an ideal choice for both stock replacements and performance upgrades. It delivers 340 liters per hour of flow at 43 psi, with an operational pressure range of 43-90 psi. The pump is designed for both gasoline and E85/ethanol fuels, and comes with a complete installation kit including fuel strainers, hoses, O-rings, and wiring connectors .

Each KEMSO pump is individually tested for quality and performance, and the company stands behind its products with a lifetime warranty. This means you can buy with confidence, knowing that your investment is protected for as long as you own your vehicle. Whether you are replacing a failed factory pump or upgrading for a built engine with bigger injectors, KEMSO has the solution you need.

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Conclusion

The fuel pump relay on a 1990 Nissan 300ZX is located behind the driver's side kick panel, directly below the hood release cable. It is a green relay mounted on the metal bracket near the fuse panel. This location is the same for both naturally aspirated and twin-turbo models.

If your 300ZX cranks but won't start, start your diagnosis by checking the fuel pump relay. Listen for the relay clicking when you turn the key to the ON position. Test the relay with a multimeter to confirm it is working properly. If the relay is faulty, replace it with a new one from your local auto parts store.

Remember that the fuel pump relay is just one component of the fuel delivery system. Also check the fuel pump fuse, the Fuel Pump Control Unit under the driver's seat, and the fuel pump itself inside the fuel tank. A systematic approach to diagnosis will save you time and money.

For the best replacement fuel pump for your 1990 Nissan 300ZX, visit KEMSO Racing at https://www.kemsoracing.com/. Their high-performance fuel pumps come with a lifetime warranty and are designed to deliver reliable performance for years to come.


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