Ignition Coil and Iridium Spark Plugs for GMC Envoy XL (2002-2005) 4.2L

Direct-Replacement Ignition Coil and Iridium Spark Plug Kit for 2002-2005 GMC Envoy XL

What it Does: The Ignition Coil and Iridium Spark Plug Kit restores factory secondary ignition voltage and combustion efficiency on the 2002-2005 GMC Envoy XL to eliminate engine misfires, rough idle, and unburned fuel dumping.

The Stock GMC Envoy XL Secondary Ignition Breakdown

The factory coil-on-plug assemblies on the GMT368 platform sit directly atop the cylinder head inside recessed plug wells, exposing them to continuous high-temperature thermal cycling. Over time, the OEM coil potting epoxy hardens and develops micro-fractures, causing internal dielectric breakdown and secondary winding arcing under load. Simultaneously, aged factory spark plugs suffer center electrode erosion, widening the spark gap past factory specifications. This enlarged gap elevates the kilovolt demand on the aging ignition coils, accelerating coil failure and throwing diagnostic trouble codes P0300 through P0306 across the Atlas LL8 inline-six engine.

The Engineering Solution

This direct-fit kit resolves ignition dropouts by pairing high-output pencil coils with precision-engineered iridium spark plugs matching interchange numbers UF303 and 68070492AB. The replacement coils feature impact-resistant, high-dielectric PBT housings, copper core windings, and high-temp silicone boots that isolate secondary voltage and block flashover. Paired with fine-wire iridium center electrodes, the spark plugs resist electrical erosion, lower required ignition voltage, and maintain a consistent flame kernel propagation under heavy throttle transitions and sustained highway loads.

Technical Specifications

Compatibility

• 2002-2005 GMC Envoy XL SLE 4.2L L6
• 2002-2005 GMC Envoy XL SLT 4.2L L6

Frequently Asked Questions

Does this fit the GMT368 Envoy XL?
Yes, this is a direct fit for the 2002-2005 GMC Envoy XL equipped with the Atlas LL8 4.2L Vortec engine.

Are these spark plugs pre-gapped?
Yes, the iridium plugs are pre-set to factory specifications, though verifying proper gap with a feeler gauge prior to installation is recommended.

The GMC Towing & Utility Standard

Engineered for full-size family hauling and sustained trailer pulling, the extended GMT368 chassis demands continuous, uninterrupted spark delivery to safeguard catalytic converter life and maintain stable air-fuel ratios under load.