For a misfire in a 2003 Ford Explorer equipped with the 4.0L SOHC V6 engine, the correct firing order and related component locations are critical.
4.0L SOHC V6 Firing Order
The correct firing order is: 1-4-2-5-3-6.
Always double-check this sequence.
Cylinder Location & Coil Pack Identification
- Driver's Side (Front to Rear): Cylinder 1 (Front) Cylinder 2 (Middle) Cylinder 3 (Rear)
- Passenger Side (Front to Rear): Cylinder 4 (Front) Cylinder 5 (Middle) Cylinder 6 (Rear)
- Coil Pack Locations: The spark plug wires originate from three coil packs. These are typically mounted together on a bracket located at the front-top center of the engine, just behind the alternator and idler pulley area.
- Coil Pack Terminals: Each coil pack has two terminals, firing two cylinders each (Coil A: Cylinders 1 & 4, Coil B: Cylinders 2 & 5, Coil C: Cylinders 3 & 6).
Diagnosing & Fixing Misfires Related to Firing Order
- Verify Wires: Visually inspect each spark plug wire carefully. Trace each wire from the correct cylinder spark plug to the correct coil pack terminal as defined by the cylinder pairings (1/4, 2/5, 3/6) and firing order. Mismatched wire routing is a common cause of misfires.
- Inspect Wires & Connectors: Check wires for cracks, burns, brittleness, or arcing marks. Ensure terminals at both the coil pack and spark plug are clean, undamaged, and firmly seated. Pull each wire gently near the boot to check for loose retention.
- Check Coil Packs: Swap the coil pack corresponding to the misfiring cylinder (or pair) with a coil pack serving a cylinder that's firing correctly (e.g., swap Coil A & Coil C if cylinder 1 is misfiring). Clear diagnostic trouble codes and re-test. If the misfire moves to the other cylinder(s) served by the swapped coil, replace that coil pack.
- Inspect Spark Plugs: Remove the plugs from the misfiring cylinders. Check for fouling (oil, carbon, coolant), excessive wear, incorrect gap, cracked porcelain, or damage. Replace plugs if any issues are found, adhering to the specified plug type and gap.
- Check COP Boots: If your engine uses Coil-On-Plug (some late models), the boots connecting the coil directly to the spark plug can crack or become conductive. Replace any damaged boots.
- Reset PCM: After repairs, disconnect the battery negative cable for 10-15 minutes to reset the PCM and clear misfire history.
Essential Tips
- Replace spark plug wires one at a time to maintain correct routing order. Labeling wires before removal is highly recommended.
- Use a suitable spark plug socket and wrench extensions to safely reach rear plugs. Beware of debris falling into spark plug wells.
- Diagnose by the specific cylinder code (e.g., P0301 = Cyl 1 misfire). Ignoring a specific code wastes time.
- Avoid generic scan tools; use advanced diagnostics if misfire persists after verifying ignition basics, as causes can include fuel injectors, compression issues, or timing chain problems (less frequent on 2003 SOHC).