The 2002 Ford 7.3L Power Stroke Diesel Fuel Pump Relay Location: Find It Fast & Fix Issues

The fuel pump relay (FP Relay) for a 2002 Ford Super Duty with the 7.3L Power Stroke diesel engine is located in the Underhood Power Distribution Box (PDB), a black rectangular box mounted on the driver's side fender apron near the firewall. This relay is crucial for powering the electric fuel pump that feeds high-pressure oil to the engine's HEUI injector system. If you're experiencing hard starts, no-starts, or performance issues, locating and inspecting this relay is a primary troubleshooting step.

Pinpointing the Relay in the Underhood Power Distribution Box

The Underhood Power Distribution Box (PDB) is your central hub for many critical electrical components and fuses. On the 2002 Ford Super Duty (F-250, F-350, F-450, F-550, Excursion) equipped with the 7.3L Power Stroke, find this box near the back of the driver's side engine compartment. It's typically positioned on the top part of the inner fender wall, fairly close to the brake master cylinder and firewall. It's a substantial black plastic box with a large wiring harness plugged into its bottom and multiple relays and fuses inside. You must lift or remove its cover to access the internal components. The lid usually has a diagram indicating the position of each fuse and relay.

  • Relay Position Within the PDB: Once you open the PDB cover and look at the diagram or the actual slots inside, find the slot specifically designated for the Fuel Pump (FP) Relay. Importantly, Ford utilized two different suppliers for these power distribution modules during the 2002 model year (typically distinguished by "Motorcraft" or "Bosh" branding). This means the exact slot number or position of the FP relay within the box can differ:
    • Motorcraft-Style PDB: The FP Relay is frequently located in position #301. This relay is likely a standard black plastic cube relay with four or five spade terminals underneath.
    • Bosh-Style PDB: The FP Relay is often located in position #304. It looks similar to the Motorcraft relay. Both types of boxes will clearly label the slot as "Fuel Pump" or "FP" Relay on the internal diagram or molded plastic near the slot.
    • Critical Action: Do not assume position based solely on numbering conventions. Always verify the label inside your specific PDB or on its lid diagram. Look for the words "Fuel Pump," "FP Relay," or the function "Fuel Pump" next to one of the relay sockets. Counting positions from a known starting point using the diagram is essential. If the lid diagram is missing or unreadable, searching online for the specific diagram matching your truck's VIN or PDB brand can help.

What the Fuel Pump Relay Looks Like

The FP Relay itself is a standard automotive cube relay, roughly 1 to 1.5 inches square. Most are black plastic. It will have four or five electrical spade terminals extending from its bottom edge, which plug down into the socket in the PDB. The top surface usually has a diagram showing the terminal numbering (e.g., 85, 86, 87, 30, sometimes 87a) and the internal circuit. Often, there might be a part number molded into the plastic casing (common Ford numbers include F5TZ-9345-A, F65Z-9345-AA, or industry numbers like RY199, or simply the word "RELAY" along with an amperage rating like 20A/30A). Crucially, it will not be a blade-type fuse. Don't confuse it with the larger maxi-fuses or standard fuses also present in the PDB.

Why Locating This Relay Matters

The FP Relay is controlled by the Powertrain Control Module (PCM). When you turn the ignition key to the "ON" position (or the "Wait to Start" light goes out for a few seconds in diesel applications), the PCM sends a ground signal to the relay coil, energizing it. This completes the high-current circuit between battery power (coming in via a large fuse, often in the same PDB) and the fuel pump. No relay operation means no power to the pump, leading directly to a no-start condition. A failing relay (intermittent, sticking, burned contacts) causes hard starts, stalling, engine cutting out, or loss of power under load – symptoms mimicking a failing fuel pump itself. Swapping a suspect FP relay with a known good, identical relay from another non-critical position in the PDB (like the horn relay, blower motor relay, or a/c clutch relay - but only if they are the exact same part!) is one of the easiest and fastest diagnostic steps you can take.

Safety Precautions Before Handling

  • Turn Off the Engine: Make absolutely sure the engine is off.
  • Turn Off the Ignition Key: Remove the key from the ignition cylinder to prevent accidental starting and eliminate power to most circuits.
  • Consider Battery Disconnect (Optional but Recommended for Testing/Removal): Disconnecting the negative (-) battery terminal provides the highest level of safety against accidental short circuits while probing or removing components in the PDB.
  • Fuel System Caution: Understand that while the fuel pump relay controls the pump, the fuel system itself remains under pressure. Do not open fuel lines immediately after shutting down the engine. Allow time for pressure to dissipate naturally.

Testing or Swapping the FP Relay

  1. Locate: Use the steps above to find the PDB and identify the FP Relay slot using the diagram/label.
  2. Identify Swappable Relays: Locate another relay in the PDB that is identical to the FP Relay in size, shape, number of terminals, and markings (like the horn or a/c clutch relay). NEVER swap in a relay that doesn't perfectly match.
  3. Swap: Carefully pull the FP relay straight up and out of its socket. Install the known good relay (e.g., the horn relay) into the FP relay socket. Reinstall the original FP relay into the socket where the known good relay came from (e.g., the horn socket).
  4. Test: Try starting the engine. If the symptoms disappear or the engine starts normally, the original FP relay was likely faulty. If the problem persists, the relay might not be the cause (though it's not guaranteed – the "known good" relay could also be weak, or other wiring/fuse/pump issues exist).
  5. Formal Electrical Testing: Using a multimeter, you can test the relay:
    • Coil Test (Terminals 85 & 86): Set the meter to Ohms (Ω). Measure resistance across the coil terminals (usually 85 and 86). Expect between 50Ω and 150Ω typically. An open circuit (OL) or very high resistance indicates a bad coil. Very low resistance (near 0Ω) suggests a shorted coil.
    • Contact Test (Terminals 30 & 87): Set the meter to continuity or Ohms. With the relay de-energized, measure between the common power terminal (30) and the normally open contact (87). There should be no continuity. Apply the correct coil voltage (usually 12V) to terminals 85 (+) and 86 (-) – you should hear an audible click and the meter should show continuity (or very low resistance) between terminals 30 and 87. Lack of click or lack of continuity when powered means bad contacts.

Common Misconceptions and Related Components

  • Fuse Confusion: The FP Relay controls the power circuit, but the actual high-current power flows through a large fuse, also typically located in the Underhood PDB. You MUST also check this fuse. Find the fuse labeled "Fuel Pump" (or similar) and check for continuity – a blown fuse will cause identical no-start symptoms regardless of the relay's condition. Common fuse amperage is 20A or 30A.
  • Not an Injector Driver Relay: While the fuel pump relay is essential for providing fuel pressure, it is not involved in the injection timing or individual injector firing. The PCM uses separate outputs via the Injector Driver Module (IDM) located elsewhere to control the injector solenoids.
  • Glow Plug System is Separate: The Glow Plug Relay (GPR) is a much larger, heavy-duty relay, usually mounted near the firewall or on the engine valley. It powers the glow plugs during cold starts and is entirely separate from the fuel pump circuit.
  • 2003 Differences: The 2003 6.0L Power Stroke diesel has a very different fuel system and relay layout. Information for 2002 7.3L is specific to that model year and engine.
  • Idle Validation Switch: While not controlling the relay directly, a faulty Idle Validation Switch (IVS) on the accelerator pedal assembly can cause confusing no-start or stalling symptoms, as it signals the PCM whether the pedal is depressed or not. Diagnosing this may be necessary if relay and fuse checks are okay but symptoms persist.
  • Fuel Pump Itself: A failing fuel pump is common. If swapping the relay doesn't help, and the fuse is good, testing fuel pressure is the next crucial step using a gauge designed for the HEUI system's high pressures. A lack of pressure confirms an issue, which could be the pump or associated wiring.

Beyond the Relay: Systematic Troubleshooting

Locating and testing the FP Relay is step one. If issues remain, proceed methodically:

  1. Check ALL Relevant Fuses: Double-check the FP fuse. Also check other main power fuses in the PDB and the battery junction fuse box (interior fuse panel).
  2. Verify Inertia Switch: The inertia safety switch, usually located behind a passenger kick panel, can shut off fuel pump power in an accident. Ensure it hasn't tripped (check its reset button).
  3. Check for Power and Ground Signals:
    • At the Relay Socket: With the ignition "ON", probe the socket terminal for the relay's coil control (typically terminal 86). It should have battery voltage (+12V). Probe the coil ground terminal (85) – this goes to the PCM. Using a test light or multimeter referenced to battery positive, terminal 85 should go to ground when the ignition is cycled (you may see it ground briefly during key-on). Requires precise identification of socket terminals.
    • At the Fuel Pump Connector: Located near the tank. Access is often under the truck or through an access panel. Verify power is present at the pump connector (disconnected) when the ignition is cycled and the relay should be active. Check the ground circuit for the pump.
  4. Test Fuel Pressure: This is mandatory. Use a high-pressure fuel gauge designed for the 7.3L HEUI system (capable of 500+ PSI). Connect to the test port on the driver's side fuel filter head. Cycle the ignition. Does pressure build to the specified range (around 55-65 PSI minimum at idle, higher under load)? Low or no pressure after confirming electrical issues are resolved points to a failing pump or restrictions in the pickup/filters.
  5. Inspect Wiring: Look for damaged, frayed, or corroded wiring along the entire path from the PDB relay to the inertia switch, through the chassis harness, to the fuel pump at the tank. Pay attention to spots where wiring passes through the frame or near sharp edges.

Replacement and Prevention

If you determine the FP relay is faulty:

  • Purchase the Correct Part: Buy a direct replacement relay matching the exact specification found in your PDB. Avoid cheap, generic relays for critical components – OEM or reputable brands (like Standard Motor Products RY199 or equivalent) are preferred. Carry a spare.
  • Installation: Simply push the new relay firmly down into the correct socket until it clicks home.
  • Relay Life: Relays are electro-mechanical and wear out. Heat and vibration accelerate failure. The FP relay cycles frequently. Consider carrying a known good replacement relay in your truck as an inexpensive insurance policy against roadside breakdowns.

Conclusion

For the 2002 Ford Super Duty 7.3L Power Stroke, the critical Fuel Pump Relay (FP Relay) is inside the black Underhood Power Distribution Box (PDB) mounted on the driver's side fender near the firewall. Always identify its precise location within your PDB using the internal diagram or lid label. Knowing where this relay is empowers you to quickly check, swap, or test it as a fundamental step in diagnosing fuel-related no-start, stalling, or power loss issues. Always combine this with checking the FP fuse and systematically confirming power signals and fuel pressure for an accurate diagnosis. Locating and testing this relay is an essential piece of DIY maintenance for the reliable 7.3L Power Stroke.

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