High Pressure Fuel Pump

This procedure replaces the high pressure fuel pump on the 3.5L EcoBoost engine, which is mounted on the engine and supplies fuel to the direct injection system.

Warnings

Tools required

Parts

• High pressure fuel pump × 1 — Motorcraft CM5331 or equivalent
• Fuel pump O-rings and seals kit × 1 — Use OEM specification
• Fuel line O-rings × 4 — Use OEM specification

Preparation

1. Park vehicle on level ground and engage parking brake
2. Ensure engine is completely cold (has not been run for at least 2 hours)
3. Disconnect negative battery cable and wait 5 minutes for capacitor discharge
4. Remove engine cover by pulling upward on front edge then lifting off
5. Clean the entire area around the high pressure fuel pump with shop towels to prevent debris contamination
6. Place catch pan and absorbent material under the work area to catch fuel spillage
7. Have fire extinguisher positioned within immediate reach

Procedure

1. 1

   Relieve fuel system pressure
   Locate the fuel rail pressure relief valve on the driver side fuel rail (under black cap). Attach fuel pressure gauge with Schrader valve adapter. Slowly open the valve to relieve pressure into catch pan. Monitor gauge until pressure reads 0 PSI. Close valve and remove gauge. Reinstall protective cap.
   ⚠️Stand clear of the relief valve. Fuel will spray out under high pressure. Wear safety glasses and fuel-resistant gloves.
2. 2

   Disconnect low pressure fuel supply line
   Locate the low pressure fuel supply line connecting to the high pressure pump inlet on the driver side of the engine. Use the appropriate fuel line disconnect tool to release the quick-connect fitting. Gently pull the line away from the pump. Cap the line immediately with a clean plug to prevent contamination. Allow residual fuel to drain into catch pan.
   ⚠Expect fuel spillage. Have catch pan positioned directly under the connection point.
3. 3

   Disconnect high pressure fuel outlet line
   Locate the high pressure fuel line connection on top of the pump. This is a threaded fitting with a union nut. Hold the pump body fitting stationary with one wrench while loosening the union nut with another wrench (typically 17mm). Once loose, carefully unthread by hand. Remove and discard the old O-rings from both sides of the connection. Cap both the pump outlet and fuel line to prevent contamination.
   ⚠Even after pressure relief, residual fuel will be present. Work slowly and have towels ready.
   Torque spec

   Fuel Line Fittings25 Nm (18 lb-ft)
4. 4

   Disconnect electrical connector
   Locate the electrical connector on the high pressure fuel pump. Press the tab and pull the connector straight away from the pump. Inspect connector terminals for corrosion or damage. If corrosion is present, clean with electrical contact cleaner and allow to dry completely before reassembly.
   ℹ️Do not pull on wires; grip the connector body only.
5. 5

   Remove pump mounting bolts
   Locate the three mounting bolts securing the high pressure fuel pump to the engine block (driver side, near the front of the engine valley). Remove these bolts using appropriate socket. Keep bolts in a clean container for inspection and potential reuse.
   Torque spec

   Mounting Bolts31 Nm (23 lb-ft)
6. 6

   Remove high pressure fuel pump
   Carefully pull the pump straight out from the engine block. The pump has a drive coupling that engages with a camshaft lobe, so you may need to rotate the pump slightly while pulling. Once clear of the drive coupling, remove the pump completely. Immediately cover the engine opening with a clean, lint-free cloth to prevent debris entry.
   ⚠Do not drop the pump or allow it to strike hard surfaces, as this can damage the precision components even if you plan to discard it.
   ⚠️CRITICAL: Do not allow ANY debris, dirt, or foreign material to enter the engine opening. Even small particles can cause catastrophic engine damage.
7. 7

   Inspect drive coupling and mounting surface
   Remove the protective cloth briefly and inspect the drive coupling in the engine block. Verify it is not damaged and rotates freely. Check the mounting surface on the engine block for damage, cracks, or debris. Clean the mounting surface thoroughly with lint-free cloth. Inspect the old pump O-ring seal location for any remaining seal material and remove completely. Re-cover opening immediately after inspection.
   ℹ️The drive coupling should rotate smoothly by hand. If it feels rough or binds, further engine inspection is required before proceeding.
8. 8

   Prepare new high pressure fuel pump
   Unpack new pump and verify it matches the old pump exactly. Install new O-ring seal on the pump body in the groove provided (use O-ring from new pump kit). Lightly lubricate the O-ring with clean engine oil or the small amount of fuel on your gloved finger. Do NOT use petroleum jelly or other lubricants. Verify the pump drive coupling end is clean and free of debris.
   ⚠Use only the O-rings provided with the new pump or OEM replacement O-rings. Aftermarket O-rings may not withstand fuel pressure and temperature.
9. 9

   Install new high pressure fuel pump
   Remove protective cloth from engine opening. Align the new pump drive coupling with the engine drive coupling. You may need to slowly rotate the pump to align the coupling teeth. Once aligned, push the pump straight into the mounting bore until it seats fully against the engine block mounting surface. Verify the pump is fully seated and mounting bolt holes are aligned.
   ⚠Do not force the pump. If it does not slide in smoothly, remove it and check alignment. Forcing can damage the drive coupling or pump.
10. 10

    Install mounting bolts
    Install the three mounting bolts finger-tight first to ensure proper alignment. Then torque bolts in a star pattern to specification using a torque wrench. Verify pump is secure and does not move when pulled gently.
    Torque spec

    Mounting Bolts31 Nm (23 lb-ft)
11. 11

    Reconnect high pressure fuel outlet line
    Install new O-rings on both sides of the high pressure line connection (use O-rings from kit). Lightly lubricate O-rings with clean fuel on gloved finger. Thread union nut by hand onto pump outlet fitting until hand-tight. Hold pump fitting stationary with one wrench and torque union nut to specification with torque wrench.
    ⚠CRITICAL: Do not overtighten. Exceeding torque specification can damage the fitting and cause fuel leaks under high pressure.
    Torque spec

    Fuel Line Fittings25 Nm (18 lb-ft)
12. 12

    Reconnect low pressure fuel supply line
    Remove cap from low pressure fuel line. Install new O-rings on the quick-connect fitting (use O-rings from kit). Push the fuel line straight onto the pump inlet until you hear and feel a distinct click indicating the fitting is locked. Pull back gently on the line to verify it is secure and will not separate.
    ℹ️The line must click into place. If it does not click, remove it, inspect O-rings and fitting for damage, and try again.
13. 13

    Reconnect electrical connector
    Align electrical connector with pump terminal and push straight on until it clicks securely into place. Tug gently on connector to verify it is locked.
14. 14

    Prime fuel system and check for leaks
    Reconnect negative battery cable. Turn ignition key to ON position (do not start engine) for 5 seconds, then OFF for 5 seconds. Repeat this cycle 5 times to prime the fuel system and build pressure. After final cycle, carefully inspect all fuel connections at the pump for any signs of fuel leakage. Use a clean white cloth to wipe around connections and check for fuel traces.
    ⚠️If ANY fuel leakage is detected, immediately turn off ignition, relieve fuel pressure, and correct the issue before proceeding. Do not attempt to start the engine with a fuel leak present.
15. 15

    Start engine and final leak check
    Start the engine and allow it to idle. Carefully inspect all fuel pump connections while engine is running. Look and feel for any fuel spray, drips, or seepage. Check electrical connector for proper seating. Listen for unusual noises from the pump area. Allow engine to run for 2-3 minutes while monitoring. If any leaks or unusual noises are detected, shut down immediately and investigate.
    ⚠️Stand clear of the pump area during initial startup. If a connection fails under pressure, fuel will spray forcefully.
    ⚠If the engine fails to start, runs rough, or the check engine light illuminates, there may be an issue with the installation. Do not continue driving until the issue is diagnosed and corrected.

Reassembly

1. Clean any spilled fuel from engine bay components using shop towels
2. Reinstall engine cover by aligning rear tabs first, then pressing down on front until it clicks into place
3. Properly dispose of old fuel pump, fuel-soaked rags, and used O-rings according to local regulations
4. Allow vehicle to ventilate for at least 15 minutes before moving to enclosed space

Verification

• With engine at operating temperature, verify no fuel odor is present in engine bay
• Check that engine idles smoothly with no hesitation or rough running
• Perform a test drive and verify normal acceleration with no loss of power or hesitation
• Re-inspect all fuel connections after test drive for any signs of seepage or leakage
• Verify no fuel odor in cabin during or after test drive
• Check for diagnostic trouble codes using OBD-II scanner; no fuel system codes should be present
• Monitor fuel pressure with scanner (if equipped) - should read approximately 500-2,175 PSI during operation depending on load

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