Use the exact plug Chrysler specified — Champion copper RC12MCC4 on the 4.0L (gap 0.035"), Champion platinum RC7PYCB4 on the 4.7L (gap 0.040"). Substituting "upgrades" can cause pre-ignition on the 4.0 and rough running on the 4.7.
The 4.0L straight-six and the 4.7L PowerTech V8 both use unusual spark plug specs, and both punish builders who try to upgrade to a "better" plug. Don't run NGK Iridium IX on either engine — they will work, but the ground electrode geometry is wrong and you'll get misfires under load. The factory Champions are not premium plugs, but they are the right plugs.
The 4.0L: 6 plugs in a straight line on the passenger side of the head. Pull the boots straight up (twist first if they've been on a while — silicone bonds to ceramic). 5/8" plug socket, 3/8" ratchet, swivel extension makes it more manageable. Plugs gap to 0.035". Anti-seize on the threads (small amount — too much can ground the plug), dielectric grease in the boot. Torque to 27 ft-lbs.
The 4.7L: 8 plugs, one per cylinder, plus a coil-on-plug ignition system. Pull the harness connector at each coil, remove the 7mm coil bolt, lift the coil, then unscrew the plug. The Standard 4.7L (VIN code N) uses RC12MCC4 — copper core, gap 0.035". The HO 4.7L (VIN code J, 2002–2004) uses RC7PYCB4 — platinum-tipped, gap 0.040". Check the VIN before you buy: the eighth character tells you which engine (N or J). Torque to 13 ft-lbs on the 4.7 — these aluminum heads will strip if you overtighten, so use a torque wrench, not a feel-it tighten.
Service interval: 30,000 miles on the 4.0, 30,000 miles on the 4.7 Standard, 100,000 miles on the 4.7 HO platinums (though most owners do them at 60–80k since the plugs are cheap insurance against a misfire on a coil-on-plug system).
| Part | Vendor | Est. price |
|---|---|---|
| Champion RC12MCC4 — 4.0L (set of 6) | Champion / Mopar SPRC12MCC4 | ~$25 |
| Champion RC7PYCB4 — 4.7L Standard (set of 8) | Champion / Mopar SPRC7PYCB4 | ~$70 |
| Champion RC7PYCB4 — 4.7L HO (set of 8) | Champion / Mopar SPRC7PYCB4 | ~$85 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.