1999 Jeep Cherokee Fuel Pump Replacement: A Comprehensive Step-by-Step Guide (With Essential Safety & Tips)

Replacing the fuel pump in your 1999 Jeep Cherokee (XJ) is a demanding but achievable task for experienced DIY mechanics. This extensive guide walks you through the entire process safely and methodically, covering necessary tools, detailed steps, crucial safety warnings, compatibility checks, testing procedures, and helpful tips based on years of hands-on experience. The pump assembly is located inside the fuel tank, requiring tank removal. Success requires meticulous preparation, adherence to safety protocols concerning flammable gasoline fumes, and careful handling of fuel lines and electrical connectors. Allow a full day for this project.

Why Fuel Pumps Fail & Signs You Need a Replacement (1999 Cherokee Specific)
The 1999 Jeep Cherokee uses an electric fuel pump submerged in the fuel tank. This fuel cools and lubricates the pump motor. Common failure causes include running the tank consistently low (causing overheating), internal electrical faults, clogged pump screens (sock filter), wear over time (often 100,000+ miles but highly variable), and contamination from tank debris or rust. Symptoms pointing directly to fuel pump failure in this specific model year include:

• Engine Cranking But Not Starting: If the engine turns over strongly but refuses to fire, and you've eliminated obvious causes like a dead battery or starter, fuel delivery is a prime suspect.
• Loss of Power During Acceleration: A failing pump cannot maintain required fuel pressure under load, causing noticeable hesitation or stuttering.
• Engine Sputtering or Stalling at High Speeds: Similar to power loss but occurs when sustained higher fuel flow is demanded.
• Sudden Stalling Followed by Difficulty Restarting: The pump overheats or fails, stopping fuel flow. It may briefly work again after cooling down.
• Whining or Humming Noise from the Rear: A significantly louder-than-normal whine or a high-pitched, distressed sound emanating from beneath the rear seats often precedes failure.
• No Audible Pump Prime: When you turn the ignition key to "ON" (without starting), a healthy pump should run for 2-3 seconds to pressurize the system. Listen carefully near the fuel tank access point under the rear seat cushion. Silence indicates an issue.
  Crucial Pre-Replacement Diagnostics: Before assuming the pump is faulty, perform these critical checks specific to the 1999 Cherokee:

1. Confirm Adequate Fuel: Ensure the gauge is accurate and there is actually fuel in the tank.
2. Check Inertia Safety Switch: Located in the passenger footwell near the kick panel. If triggered in an accident (or sometimes by a sharp bump), it cuts power to the pump. Push the reset button firmly.
3. Fuel Pump Relay: Swap the fuel pump relay with an identical relay from another circuit (like the horn or A/C) in the under-hood Power Distribution Center (PDC). If the pump now primes, replace the relay.
4. Fusible Link & Main Fuse: Inspect the fusible link near the PDC/battery and the main fuel pump fuse within the PDC. Test for continuity.
5. Fuel Pressure Test: THIS IS THE MOST CONCLUSIVE DIAGNOSTIC STEP. Locate the Schrader valve fuel pressure test port on the fuel rail near the engine intake manifold. Rent a fuel pressure gauge kit. Turn the key to ON (do not start) and observe the gauge. The 1999 Cherokee 4.0L requires 49 psi ± 5 psi system pressure. If it reads zero or significantly low pressure during the prime cycle, the pump isn't working or delivering enough pressure. Check for pressure holding after prime – a rapid drop can indicate a faulty pump check valve or leaking injector.

Safety is Paramount: Non-Negotiable Precautions
Gasoline is extremely flammable and explosive. Working with fuel systems demands the highest level of caution:

1. Work Outdoors or in VERY Well-Ventilated Space: NEVER work in a garage attached to your house or any confined area without massive airflow. Gasoline fumes are heavier than air and can pool; a single spark can cause an explosion.
2. NO Ignition Sources: Prohibit open flames, sparks, cigarettes, pilot lights, anything that can ignite fumes within at least 50 feet of your workspace. Disconnect the vehicle's battery negative terminal before starting any work.
3. Relieve Fuel System Pressure: Essential to prevent a pressurized fuel spray. Locate the fuel pump relay in the PDC. Start the engine. With the engine running, remove the fuel pump relay; the engine will stall once residual pressure is depleted. Attempt to start the engine again for 2 seconds to further drain pressure. Crank no more than twice.
4. Drain the Fuel Tank COMPLETELY: This is critical! Removing a full or partially full tank is dangerous, heavy, and messy. Use a transfer pump (hand-operated or safe electric pump) to remove nearly all fuel into appropriate gasoline containers designed for safe storage. Leave about 1 gallon or less in the tank for manageable weight and handling. Avoid siphoning by mouth – use a pump.
5. Wear Safety Gear: Chemical-resistant gloves (like nitrile), safety glasses, long sleeves, and pants. Gasoline on skin can cause irritation and long-term health issues.
6. Have a Fire Extinguisher Ready: Keep a large Class B (flammable liquids) or ABC fire extinguisher immediately accessible. Know how to use it.
7. Minimize Spills, Contain & Clean Immediately: Have absorbent pads or kitty litter ready. Gasoline vapors are the primary hazard – clean spills thoroughly and allow the area to ventilate.

Gathering the Correct Parts, Tools, & Supplies
Success hinges on having the right components and equipment ready before you begin.

Essential Parts:

• Fuel Pump Assembly for 1999 Jeep Cherokee: Must be SPECIFICALLY for the 1999 Cherokee (XJ) with the 4.0L engine. Brands vary (Bosch, Airtex, Carter, Delphi, Spectra Premium). Consider OE Mopar for best longevity. Verify with supplier using your VIN.
• Fuel Pump Module O-Ring/Gasket Kit: A NEW, high-quality rubber o-ring seal for where the pump assembly mounts to the tank. DO NOT reuse the old one. Failure here causes leaks and fumes. Often comes with the pump assembly but verify.
• Fuel Filter: Replace the inline fuel filter while you have access – it's cheap insurance (located along the frame rail). Ensure it matches the 1999 4.0L model.
• (Optional but Recommended) Tank Strap Insulators: The rubber cushions where the metal tank straps wrap the tank often rot. Best to replace them proactively.

Essential Tools & Supplies:

• Floor Jack & Jack Stands: Must be rated for vehicle weight. Minimum of 2-ton capacity. NEVER work under a vehicle supported only by a jack.
• Wheel Chocks: For front wheels.
• Large Drain Pan: Larger than the tank's capacity.
• Fuel Transfer Pump: Safe for gasoline (hand or battery-operated siphon pump).
• Basic Hand Tools: Sockets (1/2", 3/8", & 1/4" drive), wrenches (SAE: 1/4", 5/16", 11/32", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 13/16", 7/8"), ratchets, extensions, screwdrivers (flathead, Phillips), needle-nose pliers.
• Line Wrenches (Flare Nut Wrenches): Critical for fuel line fittings! Standard wrenches will round them off. Sizes needed: 11mm & 14mm (sometimes 3/8" & 7/16" can be used carefully). A 5/16" for the vapor line connector nuts is also needed.
• Fuel Line Disconnect Tools: Plastic tools specific for 5/16" and 3/8" quick-connect fittings (common size kits cover these). Required to release the plastic quick-connects on the vapor lines and sometimes the feed/return lines near the tank/pump.
• Torque Wrench: In-lb (especially for pump lock ring) and ft-lb (for tank straps).
• Trim Panel Removal Tools: Plastic pry tools help remove the rear seat bottom cushion to access the pump wiring and tank module cover plate.
• Penetrating Oil (Like PB Blaster): For freeing potentially rusted tank strap bolts/screws.
• Shop Towels / Absorbent Pads: For spills and cleaning.
• Safety Glasses, Chemical-Resistant Gloves.

Step-by-Step Removal Procedure

1. Depressurize & Drain: Follow safety step #3 to relieve pressure and drain the tank to nearly empty (safety step #4).
2. Disconnect Battery: Remove the negative (-) battery cable.
3. Access Fuel Pump Wiring:
   • Fold down the rear seat bottom (usually lifts straight up or pivots at hinges).
   • Locate the access panel or plate on the floor under the seat cushion (driver's side rear floor hump). Remove any screws holding it. Carefully pry off plastic plugs or clips holding the panel. Remove the panel.
   • You will see the top of the fuel pump assembly with electrical connectors and fuel/vapor lines attached.
4. Disconnect Electrical & Vapor Lines:
   • Electrical: Carefully depress any locking tabs and unplug the main electrical connector(s) to the pump.
   • Vapor Lines: Identify the smaller vapor lines. Depress the tabs on the quick-connect fittings using the appropriate 5/16" plastic disconnect tool while gently pulling the hose off the pump nipple. Be gentle; old plastic is brittle.
5. Raise & Secure the Vehicle: Park on level concrete. Chock the front wheels front and back. Jack up the rear of the Cherokee securely. Place jack stands under the designated frame jacking points near the rear axle. Ensure stands are solid and stable before going under. Give the vehicle a solid shake test. The rear wheels should be several inches off the ground for working clearance. Leave the jack lightly engaged for extra safety if possible.
6. Disconnect Fuel Lines at Tank/Pump: Locate the larger fuel feed and return lines running to the top of the pump module. Identify the connection type: hard lines with threaded fittings or quick-connects. For quick-connects, use the appropriate disconnect tool to release them. If threaded, use flare nut wrenches to disconnect. Be prepared for minor fuel spillage – have the pan under this area. Plug the lines loosely with clean shop towels or plastic caps.
7. Support the Fuel Tank: Place a large, sturdy block of wood or a transmission jack underneath the tank for support. A second person helps immensely here.
8. Remove Tank Straps:
   • Locate the two metal straps encircling the tank – one near the front, one near the rear. Each strap is held by a bolt at one end (on a frame bracket) and typically connected to a stud with a nut at the other.
   • Apply penetrating oil to the strap bolts and stud nuts beforehand if they look rusty.
   • Carefully remove the bolts and nuts using flare nut wrenches or deep sockets, supporting the tank as you do so. Keep the nuts and bolts in a safe spot. Remove the straps and note their orientation.
9. Lower the Tank: Slowly and carefully lower the support (jack, wood block) holding the tank. Lower it just enough to access the top of the pump assembly now that it's away from the vehicle floor.
10. Disconnect Remaining Lines & Wiring: Ensure all lines and the electrical connector are completely detached from the top of the pump module. If any were still connected for lowering, now is the time.
11. Remove Tank Completely: Carefully slide the tank out from under the vehicle. Set it on a stable, clean surface in your work area (like the pan).
12. Clean Tank Top Surface: Thoroughly clean the area around the fuel pump module mounting flange and lock ring on the top of the tank. Use shop towels only – avoid dirt falling into the tank.

Pump Removal & Installation

1. Remove Lock Ring: Locate the large plastic or metal lock ring holding the pump assembly into the tank. The ring has notches. Using a brass punch and a hammer (brass prevents sparks), or a dedicated lock ring spanner tool, tap the ring COUNTER-CLOCKWISE until it unscrews completely. This requires firm, steady taps.
2. Lift Out Pump Assembly: Carefully lift the entire fuel pump module straight up and out of the tank. Be mindful of the fuel level sender float arm so it doesn't bend. Have rags ready to catch residual fuel.
3. Clean Tank Interior (If Necessary): Inspect the inside of the tank. Look for significant rust, debris, or sludge. If contaminants are present, professional tank cleaning or replacement is strongly advised. Only attempt DIY cleaning with extreme caution and thorough rinsing/drying if rust is very minor; use a specialty tank sealer kit if recommended by the product for your situation.
4. Replace Fuel Filter Sock: The new pump should come with a new filter sock strainer. Remove the old sock and install the new one onto the inlet tube of the new pump assembly.
5. Replace O-Ring & Transfer Components: Remove the old O-ring from the pump module flange or tank groove. Wipe both surfaces clean. Lightly lubricate the NEW O-Ring ONLY with clean engine oil or Vaseline. DO NOT USE gasoline or other solvents! This ensures a pliable seal and prevents tearing upon installation. If applicable, transfer the fuel level sender unit (float) from the old assembly to the new one if it functions correctly and matches the new pump. Verify the new assembly includes a functional sender before deciding.
6. Install New Pump Assembly:
   • Carefully align the float arm correctly.
   • Position the pump assembly into the tank tank opening, ensuring the alignment tabs on the assembly engage with the slots in the tank opening.
   • Press firmly and evenly down, compressing the O-ring seal, until the module flange sits flush on the tank surface. Double-check the O-ring isn't pinched or rolled.
7. Install Lock Ring: Place the lock ring over the assembly flange onto the tank threads. Tap it gently CLOCKWISE using the punch/hammer until it is fully seated and tight. Ensure the ring engages all threads correctly. Refer to service manual torque specs if possible (often around 16-19 ft-lbs, but hand-tight plus secure tapping is typical). Do not overtighten plastic rings.

Fuel Tank Reinstallation

1. Lift Tank into Position: Carefully maneuver the tank back under the vehicle. Lift and position it with your support mechanism (jack, blocks).
2. Reconnect Lines & Wiring: While supporting the tank just below its mounted position, reconnect the fuel feed/return lines and vapor lines to the top of the pump module using the proper techniques (quick-connects pushed firmly until they click, threaded connections made snug with flare wrenches). Reconnect the main electrical plug firmly.
3. Secure Tank Straps: Position the straps correctly over the tank. Install the bolts and nuts loosely at first. Once both straps are positioned and connected to their studs/bolts, progressively tighten them evenly and fully. Refer to service manual torque specs if possible (generally 18-25 ft-lbs). The tank should be secure but not distorted. Ensure rubber isolators are in good shape and correctly positioned.
4. Double-Check Connections: Visually and physically ensure all fuel lines, vapor lines, and the electrical connector are securely fastened.
5. Lower Vehicle: Slowly and carefully lower the vehicle off the jack stands until the rear wheels are on the ground.
6. Reinstall Access Panel & Seat: Place the access panel back over the fuel pump wiring area. Secure it with screws/clips/plugs. Fold the rear seat bottom back into position.

Post-Installation Testing & Verification
DO NOT skip this critical phase before starting the engine!

1. Reconnect Battery: Reconnect the negative (-) battery cable.
2. Pre-Pressurization Check:
   • Turn the ignition key to the ON position (do NOT crank). Listen carefully near the rear of the Jeep. You should hear the new fuel pump run for approximately 2-3 seconds as it pressurizes the system. This is normal.
   • Inspect for Leaks: IMMEDIATELY get down under the Jeep and visually and physically inspect ALL fuel line connections (at the tank, along the frame, and at the engine rail Schrader valve), the electrical connection, and around the pump module lock ring/o-ring. Feel for wetness; sniff for strong gasoline odor. IF YOU SEE OR SMELL FUEL: TURN THE IGNITION OFF IMMEDIATELY. Disconnect the battery and re-inspect the connection where the leak is occurring. ABSOLUTELY DO NOT START THE ENGINE WITH A FUEL LEAK.
3. Pressure Check: If you have a fuel pressure gauge, attach it to the Schrader valve on the fuel rail. Turn the key to ON and observe. You should see the pressure build to approximately 49 psi. It should hold pressure reasonably well for several minutes after the pump shuts off (some drop is normal, rapid drop indicates a potential issue with a line, injector, or pump check valve). If pressure is low or drops too fast, investigate potential installation errors or faulty components before attempting to start.
4. Start the Engine: Only after confirming no leaks and correct pressure, attempt to start the engine. It may crank for a few more seconds than usual as fuel fills the rail.
5. Final Leak Check: Once the engine is running, perform another thorough visual and physical check under the vehicle for any leaks while the pump is continuously running under pressure. Also, monitor for leaks while the engine is off but under residual pressure.
6. Operational Check: Drive the vehicle. Verify normal acceleration, no hesitations, and that it doesn't stall. Monitor for a few days to ensure reliable starting and operation.

Potential Issues & Troubleshooting Post-Installation

• Engine Cranks But Won't Start:
  • Double-check the electrical connection at the pump (plugged in fully?).
  • Verify the inertia switch isn't tripped.
  • Check the fuel pump relay and fuse (power issues).
  • Ensure all fuel line disconnects are fully seated.
  • Confirm the pump activated briefly on key-ON.
  • Perform a fuel pressure test. If zero, revisit power or pump.
• Low Fuel Pressure/Rough Running:
  • Check for crimped or damaged fuel lines during installation.
  • Verify the fuel filter was installed correctly (direction arrow matters).
  • Is the fuel sock filter properly installed and unobstructed?
  • Check for leaks in the lines causing pressure drop.
• Fuel Leak Detected:
  • STOP DRIVING IMMEDIATELY.
  • Identify the source:
    • At Pump Module: Likely faulty O-ring installation (pinched, torn, reused), cracked pump housing, loose lock ring. Requires dropping tank again.
    • At Fuel Line Connections: Inadequate tightening, damaged seal/quick-connect fitting, cracked line.
• Fuel Gauge Incorrect/Erratic:
  • Did you transfer or adjust the level sender correctly? Is it properly attached to the new module?
  • Ensure the electrical connector to the pump/sender is clean and secure.
  • Check wiring between sender and gauge cluster for damage.
• Strong Gasoline Smell Inside Vehicle:
  • Often indicates a vapor leak near the top of the pump module or at vapor lines. Requires immediate attention to diagnose (soapy water bubble test on connections near pump module when key is ON can help).
  • Ensure the gas cap is sealing properly.

Cost Considerations (DIY vs. Professional)

• DIY Cost: Primarily the cost of the pump assembly ($100-$350+) and the fuel filter ($10-$30). Adding cost for tools if you need to purchase specific wrenches or the pump (around $10-$30). Total usually $120-$400+.
• Professional Cost: Labor is significant due to the tank removal. Typically ranges from $500to$1000+ in a repair shop, including parts. Dealerships usually cost more.

When to Seek Professional Help
Replacing the fuel pump is advanced DIY. Consider a professional if:

• You lack the necessary tools or physical space to perform the job safely.
• You are uncomfortable with the significant safety risks involving gasoline fumes and sparks.
• The vehicle has severe corrosion on tank straps/bolts that might make removal difficult or unsafe.
• You encounter unforeseen complications during the process (stripped fittings, major tank damage/rust discovered).
• You lack confidence in performing critical pressure testing and leak checks.
• The car is your only transportation, and you cannot afford potential downtime if complications arise.

Conclusion
Successfully replacing the fuel pump in your 1999 Jeep Cherokee requires careful planning, meticulous attention to safety procedures, patience, and the right tools. By following this detailed guide, prioritizing safety above all else, methodically completing each step, and thoroughly testing the system, you can restore reliable fuel delivery and extend the life of your Cherokee. While demanding, the substantial cost savings compared to professional labor make this a worthwhile project for capable mechanics. Never hesitate to seek professional assistance if you feel unsure about any step, especially concerning safety or complex troubleshooting.