1990 Jeep Cherokee Fuel Pump Relay: Diagnosis, Replacement, and Maintenance Guide

If your 1990 Jeep Cherokee is cranking but not starting, the fuel pump relay is one of the most common and easiest culprits to check. This small electrical component controls power to the fuel pump, and when it fails, your engine gets no fuel. The good news is that replacing it is a simple, low-cost fix that you can do yourself in minutes. Before you start replacing expensive parts like the fuel pump itself, always test the relay first. This guide will walk you through everything you need to know about the 1990 Jeep Cherokee fuel pump relay, from symptoms and testing to replacement and long-term maintenance.

What Does the Fuel Pump Relay Do?

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 relay receives a signal from the engine control unit (ECU) and closes the circuit, sending 12 volts to the fuel pump. This allows the pump to pressurize the fuel system before you start the engine. Once the engine is running, the relay keeps the pump powered as long as the engine is running.

In your 1990 Jeep Cherokee, the fuel pump relay is located in the power distribution center under the hood, typically on the right-hand (passenger) side of the engine compartment. It is a standard 4-pin or 5-pin relay that looks like a small black or gray cube. The relay is part of a larger system that includes the fuel pump, fuel pump ballast resistor (on 4.0L models), and the fuel pump fuse.

Common Symptoms of a Bad Fuel Pump Relay

A failing fuel pump relay can cause a range of symptoms that are easy to confuse with a bad fuel pump itself. Here are the most common signs to watch for:

  1. Engine Cranks But Won't Start – This is the most typical symptom. You turn the key, the starter spins the engine, but it never fires up. You may not hear the fuel pump prime when you turn the key to "ON".
  2. No Fuel Pump Prime Noise – When you turn the ignition to the "ON" position (without cranking), you should hear a brief whirring sound from the fuel tank area. If you hear nothing, the relay or pump may be dead.
  3. Intermittent Starting or Stalling – A failing relay may work sometimes and fail others. You might experience random no-starts or the engine dying while driving, especially at highway speeds.
  4. Engine Sputters or Hesitates – If the relay is making poor contact, the fuel pump may receive inconsistent voltage, causing the engine to sputter, hesitate, or surge under load.
  5. Check Engine Light Illuminates – The ECU may detect a fuel system fault and trigger the check engine light. Common codes include P0230 (fuel pump primary circuit malfunction) or P0231 (fuel pump secondary circuit low).

How to Test the Fuel Pump Relay on a 1990 Jeep Cherokee

Testing the fuel pump relay is straightforward and requires only a few basic tools: a multimeter or a test light, and possibly a small screwdriver. Here is a step-by-step process:

Step 1: Locate the Relay
Open the hood and find the power distribution center (fuse box) on the right side of the engine compartment. The fuel pump relay is usually labeled on the fuse box cover or in your owner's manual. In the 1990 Cherokee, it is often marked as "Fuel Pump Relay" or "Relay B".

Step 2: Listen for the Relay Click
Have a helper turn the ignition key to the "ON" position while you listen near the relay. You should hear a distinct click sound. If you hear no click, the relay may not be receiving power, or the coil inside the relay is burned out.

Step 3: Test with a Multimeter
Remove the relay from its socket. Set your multimeter to measure resistance (ohms). Identify the relay's coil terminals (usually pins 85 and 86 on a standard 4-pin relay). Measure the resistance between these pins. A good relay coil should read between 50 and 120 ohms. If you get an open circuit (infinite resistance), the relay is dead.

Step 4: Test the Switch Contacts
With the relay removed, apply 12 volts to the coil terminals (pins 85 and 86) using a battery or power supply. You should hear a click. Then, measure continuity between the switch terminals (pins 30 and 87). When the relay is energized, these pins should show continuity (low resistance). If they do not, the relay is faulty.

Step 5: Check for Power at the Relay Socket
If the relay tests good, check if power is reaching the relay socket. Use a test light or multimeter to check for 12 volts at the socket's power terminal (usually pin 30) with the ignition on. If no power is present, check the fuel pump fuse and related wiring.

How to Replace the Fuel Pump Relay

Replacing the fuel pump relay on a 1990 Jeep Cherokee is one of the easiest repairs you can do. Here is what you need to know:

What You Need:

  • A new fuel pump relay. The standard replacement part number is 4671168E or 72472M. This relay is a 12-volt, 20-amp SPDT relay with a coil resistance of about 90 ohms.
  • Optional: a small flathead screwdriver to pry the relay out.

Step-by-Step Replacement:

  1. Disconnect the battery negative terminal to prevent any electrical shorts.
  2. Locate the relay in the power distribution center under the hood.
  3. Remove the old relay by pulling it straight up. You may need to gently wiggle it or use a small screwdriver to pry it out.
  4. Insert the new relay firmly into the same socket. Make sure it is fully seated.
  5. Reconnect the battery and test the system. Turn the key to "ON" and listen for the fuel pump prime. Then start the engine.

The entire replacement takes less than five minutes. The relay itself costs between $5 and $15 at most auto parts stores.

Fuel Pump Relay Location and Wiring Details

For the 1990 Jeep Cherokee, precise location details are important:

  • 2.5L Engine Models: The fuel pump relay is located on the right-hand side of the engine compartment. It is often near the fuse block.
  • 4.0L Engine Models: The relay is also on the right-hand side of the engine compartment, near the power distribution center.

The fuel pump relay wiring is standard for most Jeep models of this era:

  • Pin 30: Battery power (12V constant)
  • Pin 85: Ground (switched by ECU)
  • Pin 86: Ignition switch signal (12V when key is ON)
  • Pin 87: Output to fuel pump

On the 4.0L models, there is also a fuel pump ballast resistor located on the left-hand side of the engine compartment. This resistor reduces voltage to the fuel pump during low-demand conditions. If you are experiencing intermittent fuel pump issues, the ballast resistor can also be a culprit.

Why the Fuel Pump Relay Fails

Fuel pump relays can fail for several reasons. Understanding these causes can help you prevent future failures:

  1. Age and Wear – Relays have mechanical contacts that wear out over time. After 30+ years, the internal spring and contacts can weaken or corrode.
  2. Heat Exposure – The relay is located in the engine bay, which experiences high temperatures. Repeated heat cycles can degrade the internal components.
  3. Electrical Overload – A failing fuel pump that draws excessive current can damage the relay. If your relay fails repeatedly, check the fuel pump's current draw.
  4. Moisture and Corrosion – Water intrusion into the fuse box can cause corrosion on the relay pins or socket, leading to poor electrical connections.
  5. Vibration – Constant vibration from the engine and road can loosen the relay or cause internal connections to fail.

Common Mistakes to Avoid

When dealing with the fuel pump relay, avoid these common pitfalls:

  • Don't skip the diagnosis – Many people replace the fuel pump itself when the relay is the real problem. Always test the relay first.
  • Don't use the wrong relay – Make sure you buy a relay that matches the specifications. Using a relay with different pin configurations or current ratings can cause electrical problems or fire hazards.
  • Don't ignore the fuse – If the relay is bad, check the fuel pump fuse as well. A blown fuse can indicate a short circuit in the fuel pump wiring.
  • Don't forget to check the wiring – Corroded or damaged wiring can cause symptoms similar to a bad relay. Inspect the connector and wiring for damage.
  • Don't assume the relay is the only issue – A bad fuel pump can also cause relay failure. If you replace the relay and it fails again quickly, have the fuel pump tested.

Maintenance Tips to Extend Fuel Pump and Relay Life

Keeping your fuel system in good shape will help both the relay and the fuel pump last longer. Here are some practical maintenance tips:

  • Keep the fuel tank above a quarter full – Running the tank low causes the fuel pump to run hotter and reduces lubrication. The pump relies on fuel for cooling and lubrication.
  • Use quality fuel – Poor-quality fuel contains contaminants and water that can damage the pump and clog the strainer.
  • Replace the fuel filter regularly – A clogged filter forces the pump to work harder, increasing current draw and heat. This can stress the relay as well.
  • Check the fuel pump relay and fuse periodically – Inspect them for corrosion, loose connections, or signs of overheating.
  • Keep the electrical system in good condition – A weak battery or failing alternator can cause the fuel pump to operate at reduced voltage, making it work harder and run hotter.
  • Address check engine lights promptly – Fuel system fault codes can indicate developing problems that, if ignored, can damage the relay or pump.

When to Replace the Fuel Pump vs. the Relay

Sometimes it is hard to tell if the problem is the relay or the pump itself. Here is a quick guide:

  • If you hear the relay click but no fuel pump prime: The relay is likely working, and the problem is the pump itself, a blown fuse, or a wiring issue.
  • If you hear no click and no pump prime: The relay is likely not receiving power or is faulty. Test the relay first.
  • If the engine starts but stalls intermittently: This could be a failing relay, a bad fuel pump, or a faulty crank position sensor. Start with the relay because it is easier to test.
  • If the fuel pump runs continuously with the key off: The relay may be stuck closed (welded contacts). Replace the relay immediately.

A quality fuel pump lasts around 100,000 to 150,000 miles. If your Cherokee has more than 100,000 miles and you are experiencing fuel system issues, consider replacing both the pump and the relay together for peace of mind.

Recommended Replacement: KEMSO Fuel Pump

When it comes time to replace your fuel pump, choosing a high-quality part is essential for long-term reliability. KEMSO Fuel Pumps are designed as high-performance, direct OEM replacement units that meet or exceed original equipment specifications. They are built to deliver consistent fuel pressure and flow, ensuring your engine runs at its best.

KEMSO fuel pumps are engineered for durability and can handle up to 700-800 horsepower applications, making them suitable for both daily drivers and performance vehicles. They are compatible with gasoline and E85 ethanol-blended fuels, and each pump is individually tested for flow and performance before it leaves the factory.

One of the biggest advantages of choosing KEMSO is the lifetime warranty that comes with every fuel pump they sell. This warranty covers manufacturing defects and premature failure, giving you peace of mind that your investment is protected for as long as you own the vehicle. KEMSO fuel pumps are trusted by mechanics and enthusiasts alike for their durability and precision engineering.

To browse their full lineup and find the right pump for your 1990 Jeep Cherokee, visit the KEMSO official website: https://www.kemsoracing.com/. Their product lineup covers almost every make and model, and their customer support team can help you select the correct pump for your specific application.

Final Thoughts

The fuel pump relay on your 1990 Jeep Cherokee is a small but critical component. When it fails, it can leave you stranded, but diagnosing and replacing it is one of the simplest repairs you can do. Always test the relay first before replacing the fuel pump itself, as this can save you time and money.

Remember these key takeaways:

  • A bad relay causes no-start, intermittent stalling, and no fuel pump prime noise.
  • Test the relay using a multimeter or by swapping it with a known good relay.
  • Replace the relay with the correct part number (4671168E or 72472M).
  • Maintain your fuel system by keeping the tank above a quarter full, using quality fuel, and replacing the fuel filter regularly.
  • When it is time to replace the fuel pump, choose a high-quality KEMSO pump backed by a lifetime warranty.

For more information on fuel pump maintenance, diagnosis, and to shop for reliable replacement parts, visit https://www.kemsoracing.com/. Whether you drive a daily commuter, a work truck, or a performance vehicle, KEMSO offers a wide range of fuel pumps to fit your needs. Their products are trusted by mechanics and enthusiasts alike for their durability and precision engineering. Safe driving means a reliable fuel system, and that starts with a good fuel pump and a properly functioning relay.


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