1998 Ford Expedition Fuel Pump Relay Location & Essential Guide

For owners of a 1998 Ford Expedition experiencing fuel delivery problems or needing preventative maintenance, locating and understanding the fuel pump relay is crucial. The 1998 Ford Expedition fuel pump relay is located inside the engine compartment's Central Junction Box (CJB), specifically in position #10. This guide provides the detailed location, identification, function, testing, and replacement steps you need.

Identifying the Central Junction Box (CJB)

The Central Junction Box is the primary relay and fuse panel under the hood of your 1998 Expedition.

  1. Open the Hood: Securely prop open the hood of your vehicle.
  2. Locate the Battery: Stand facing the engine bay. The main battery is located on the front passenger side (right side) of the vehicle.
  3. Find the CJB: Directly behind the battery, mounted against the firewall (the vertical metal wall separating the engine bay from the passenger compartment), you will see a large, usually black, rectangular plastic box. This is the Central Junction Box. It's the main fuse/relay panel for engine compartment components.
  4. Remove the Cover: The CJB has a plastic cover secured by metal clips or tabs on its sides. Squeeze these clips firmly and lift the cover straight up to remove it. Set the cover aside safely.

Finding Relay Position #10

With the CJB cover removed, you will see rows of fuses and larger square or rectangular components – these larger components are the relays.

  1. Locate the Diagram: Often, the underside of the CJB cover has a detailed diagram or chart listing every fuse and relay position and its function. Important: Find the section on this diagram labeled "Relays" or listing positions by number. Look for position "#10" and verify it says "Fuel Pump" or "FP" or sometimes "PCM Relay" (The Power Control Module often controls the fuel pump relay circuit on this model). Keep this diagram visible.
  2. Identify Relay Position #10: Look directly at the top surface of the CJB box itself. Next to each relay socket (the place where the relay plugs in), there is usually a number molded or printed onto the plastic box. Scan these numbers carefully until you find the one labeled "10".
  3. Recognize the Relay: The relay itself is a small, cube-shaped, mostly black plastic component (approximately 1 inch square) with multiple metal electrical pins on the bottom plugged into socket #10. It may have markings like "F57B-14B192-AA" or other Ford part numbers, and a standard automotive relay diagram showing terminals 30, 85, 86, 87, and sometimes 87a. Crucially, its position in socket #10 confirms it's the fuel pump relay.
  4. Cross-Reference: If no clear markings are visible on the CJB box, or you cannot find #10, refer back to the diagram under the cover. If that diagram is missing, use the following reliable sources:
    • Owner's Manual: Check the fuse and relay section. The original owner's manual has the definitive layout.
    • Reliable Repair Database: Reputable sources like online repair manuals (Chilton, Haynes - their Expedition manual covering 1997-2002), or paid services like ALLDATA or Mitchell1 provide accurate diagrams.
    • Ford Dealership Parts Dept. or Service Manual: These have precise schematics.

What the Fuel Pump Relay Does

The fuel pump relay is a critical electronically operated switch.

  • It receives a low-power "turn on" signal from the Powertrain Control Module (PCM), triggered by turning the ignition key to "Run" or "Start."
  • This low-power signal energizes an electromagnet inside the relay.
  • The energized electromagnet physically closes heavy-duty internal switch contacts.
  • Closing these contacts allows high-amperage electrical current from the battery (via a fuse) to flow directly to the electric fuel pump located inside the fuel tank.
  • Without this relay working correctly, the fuel pump does not receive the significant power it needs to operate, and the engine cannot run.

Common Symptoms of a Failing Fuel Pump Relay

Recognize these signs that point towards the relay or its circuit:

  1. Engine Cranks But Won't Start: The starter spins the engine, but it doesn't fire. The most common symptom directly related to the fuel pump relay.
  2. Intermittent No-Start: The vehicle starts fine sometimes, but fails to start at other times, often after working fine moments before. A classic sign of a relay with failing internal contacts.
  3. No Fuel Pump Prime Sound: When you first turn the ignition key to "Run" (without cranking), you should hear a distinct humming or buzzing sound coming from under the rear of the vehicle (near the fuel tank) for about 1-3 seconds. This is the fuel pump priming. If you consistently hear NO prime sound when keying to "Run," the relay is a prime suspect. (Note: A completely failed fuel pump also causes this, so testing is needed).
  4. Vehicle Stalls While Driving: A relay failing while the engine is running can cause immediate fuel starvation and stalling, especially if contacts open intermittently.
  5. "Clicking" Sound from Relay/Engine Bay: Sometimes a failing relay will audibly chatter or rapidly click when turning the key to "Run" instead of just making a single solid "click." This indicates internal switch contacts are trying, but failing, to stay engaged.

Testing the 1998 Expedition Fuel Pump Relay

Testing the relay is straightforward before replacing it. Safety First: Ensure the ignition is OFF. Disconnect the negative battery cable if necessary for complex probing, but simple relay swap test is safer for most.

  1. Swap Test (Simplest & Often Most Reliable):
    • Locate the CJB and identify relay #10 (Fuel Pump) as described above.
    • Look for another identical relay in the CJB known to work for a less critical function. Common choices include the A/C Compressor Clutch Relay, the Blower Motor Relay, or sometimes the Horn Relay. Crucial: Verify using the diagram that the relay is identical in appearance and function pinout. DO NOT swap with significantly different relays (e.g., different size or terminal arrangement) or relays essential for engine control.
    • Carefully pull both the suspected fuel pump relay (#10) and the known-good relay straight out of their sockets.
    • Place the known-good relay into socket #10.
    • Have a helper turn the ignition key to "Run" (not start). Listen carefully near the rear wheel area (or inside the cab if very quiet) for the fuel pump prime hum. If the hum returns when the good relay is installed, the original relay in #10 is faulty and needs replacement.
    • Optionally, you could then place the suspected bad relay into the socket where the good relay came from (e.g., A/C socket) and test that function (e.g., turn on A/C to see if compressor engages or test horn).
  2. Basic Audible/Visual Inspection: With the relay removed:
    • Shake Test: Shake the relay gently. If you hear anything loose rattling inside (like broken contacts), it's definitely bad.
    • Visual: Examine the relay pins for severe corrosion or melting plastic casing. This indicates failure. Minor corrosion can be cleaned carefully with electrical contact cleaner and a brass brush.
  3. Using a Multimeter (Continuity Check):
    • Set a digital multimeter to the Ohms (Ί) continuity setting (which usually beeps).
    • Identify Terminals: Look at the relay's base or standard diagram. You need to identify terminal numbers (small, often molded next to pins). Essential terminals: 85, 86, 30, 87, (87a is usually not used).
    • Test Coil Circuit (Terminals 85 & 86): Place one probe on terminal 85, the other on terminal 86. You should read a resistance value, typically between 50 and 120 Ohms for a healthy coil. Zero Ohms (short) or infinite Ohms/open (OL) indicate a faulty coil.
    • Test Switch Contacts (Terminals 30 & 87):
      • Contacts Normally Open: Place probes on terminals 30 and 87. With the relay de-energized (not powered), you should read infinite resistance/open (OL or no beep).
      • Actuate Coil: To test if the contacts CLOSE when energized, you need to apply power to the coil. One easy way:
        • Obtain a 9-volt battery.
        • Connect the POSITIVE (+) wire from the 9V battery to relay terminal 86.
        • Connect the NEGATIVE (-) wire from the 9V battery to relay terminal 85.
        • Retest: With power applied, place your multimeter probes on terminals 30 and 87. You should now read very low resistance (< 1 Ohm) or hear a continuous beep (continuity). This means the contacts close correctly when energized.
      • If the contacts do not close (stay OL) when power is applied, the internal switch is faulty.
      • If the contacts show low resistance without power applied, they are fused closed internally and the relay is stuck "ON" (rare, but possible).

Replacing the Fuel Pump Relay

If testing confirms the relay in position #10 is faulty, replacement is simple:

  1. Purchase: Get an exact replacement relay. Using the vehicle's year, make, model, and engine size (4.6L or 5.4L V8) is usually sufficient for an auto parts store. Standard Ford relay part numbers include F5TZ-9345-AA, F6VF-14B192-AA, F57B-14B192-AA (or their functional equivalents like Standard Motor Products RY-168, BWD R1036, Bosch 0332019110). Important: Visually match the old relay to the new one ensuring pin count, pin layout, and physical size are identical.
  2. Ignition OFF: Ensure the key is in the OFF position.
  3. Locate & Remove: Identify relay position #10 in the CJB as described earlier. Grasp the faulty relay firmly and pull it straight up and out of its socket. Avoid wiggling excessively.
  4. Inspect Socket: Briefly inspect socket #10 for any signs of overheating (melted plastic), broken plastic pins, or severe corrosion. Clean sockets carefully only if minor corrosion exists, using electrical contact cleaner and a small brass brush or pin tool. If the socket is damaged, professional repair is needed.
  5. Insert New Relay: Take the new relay and align its pins perfectly with the holes in socket #10. Gently but firmly push straight down until the relay seats completely. You should feel it lock into place.
  6. Test: Before reassembling, turn the ignition key to "Run" (without cranking) and listen for the 2-3 second fuel pump prime hum. This indicates the new relay is operating.
  7. Replace CJB Cover: Put the CJB cover back on and secure the clips.
  8. Crank Engine: Attempt to start the engine. If the problem was isolated to the relay, the engine should now start and run.

Important Troubleshooting Considerations

  1. No Prime Sound After Relay Replacement: If the new relay is installed and you still do not hear the fuel pump prime sound when keying to "Run":
    • Inertia Switch: The 1998 Expedition has a fuel pump inertia safety switch, usually located on the passenger side firewall inside the cab (behind the passenger side kick panel) or sometimes on the driver's side toe panel area. If it has tripped (e.g., from a bump), reset it by firmly pushing its reset button down. A tripped inertia switch cuts power to the fuel pump.
    • Fuse Check: The fuel pump relay output is protected by a fuse. In the CJB, locate the fuel pump fuse using the diagram. Common positions are Fuse #12 (20A) or Fuse #6 (15A) - verify using the diagram! Pull it out and inspect the metal strip inside. If broken, replace with an identical amp rating fuse. Also check relevant fuses in the interior fuse panel (like PCM power).
    • Wiring Fault: Damaged wiring between the CJB, inertia switch, or fuel pump could be interrupting power.
    • Fuel Pump Failure: The fuel pump itself may have failed. Diagnosing this requires checking for voltage at the fuel pump electrical connector during prime/crank cycle or fuel pressure testing. This is a more complex task requiring specific tools.
  2. Intermittent Issues Persist: If the problem seems relay-related but persists after replacement or seems to come and go:
    • Socket Issues: Re-examine the relay socket (#10) more critically for poor pin connections, small cracks, or signs of arcing/heat damage.
    • PCM Control Circuit: The circuit that commands the relay to turn on (from PCM pin, through ignition switch, to relay coil terminal 85/86) could have an intermittent fault, such as a frayed wire or poor PCM ground.
    • Ground Issues: Poor grounds, especially G101 (on the engine block near the hood hinge passenger side), G103 (near the battery on passenger side fender), or G104 (back of engine on driver's side cylinder head), can affect relay control or pump power.

Preventative Maintenance

  • Consider replacing the fuel pump relay every 100,000 miles or as preventative maintenance during other major services if the relay is original or of unknown age. Relays can wear out internally over time due to arcing.
  • Keep the CJB cover intact and properly sealed to prevent excessive moisture and dirt intrusion. Clean any accumulated debris around it periodically.
  • Address electrical problems like poor charging system output or weak battery promptly. Low system voltage or voltage spikes put extra stress on relays.

By knowing the 1998 Ford Expedition fuel pump relay location (position #10 in the Central Junction Box behind the battery) and understanding how to identify, test, and replace it, you possess crucial troubleshooting knowledge. This information can save significant diagnostic time and money. Always prioritize safety, use accurate diagrams, and methodically test components before replacement. If unsure or testing points to deeper issues in the fuel pump circuit, consulting a qualified automotive technician is recommended.

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