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The 2002-2009 Chevy Trailblazer’s 4.2L Vortec inline-6 has a reputation for being picky about spark plugs — the wrong brand can mean rough idle or a check-engine light. Here are the plugs Trailblazer owners and forums actually recommend for this engine.
| # | Product | Price | Where to buy |
|---|---|---|---|
| 1 | ACDelco 41-103 Iridium Spark Plug | $8-$12 each | Amazon · eBay |
| 2 | NGK LTR5IX-11 Iridium IX Spark Plug | $8-$12 each | Amazon · eBay |
| 3 | Bosch 9611 Double Iridium Spark Plug | $9-$14 each | Amazon |
| 4 | Denso #5349 Spark Plug | $4-$8 each | Amazon · eBay |
| 5 | Autolite XP5263 Iridium XP Spark Plug | $6-$10 each | Amazon · eBay |
| 6 | Champion Platinum RE10PMC5 Spark Plug | $6-$10 each | Amazon · eBay |
The picks, in detail
ACDelco 41-103 Iridium Spark Plug
The GM-spec iridium plug most frequently recommended for the 4.2L I6 — the safest bet given the engine’s sensitivity to plug variation.
- Iridium center electrode
- GM-spec design for the 4.2L Vortec I6
- Most commonly cited “just use this” answer in Trailblazer forums
- Priced above basic copper plugs from other brands
NGK LTR5IX-11 Iridium IX Spark Plug
NGK’s direct-fit iridium plug for the 4.2L Trailblazer, a common alternative to the ACDelco.
- Iridium IX fine-wire electrode
- Direct fit for 2002-2009 4.2L L6
- NGK iridium plugs are frequently described by owners as performing on par with ACDelco
- Gap must be set to spec (0.040″-0.043″) on installation
Bosch 9611 Double Iridium Spark Plug
Bosch’s fine-wire double-iridium plug, direct fit for the 4.2L Trailblazer from 2002-2009.
- Iridium on both center and ground electrode
- Direct fit for 2002-2009 4.2L L6
- Dual iridium design aimed at longer service life
- Some owners report needing to double-check gap out of the box
Denso #5349 Spark Plug
Denso’s OE-equivalent plug for the 4.2L Trailblazer, a budget-friendly alternative to the iridium options.
- Direct fit for 4.2L Trailblazer/Envoy
- U-groove ground electrode design
- Lower cost than the iridium options here
- Standard electrode design, shorter expected service life than iridium plugs
Autolite XP5263 Iridium XP Spark Plug
Autolite’s iridium plug for the 4.2L I6, a lower-cost iridium alternative to ACDelco or NGK.
- Iridium XP fine-wire design
- Pre-set gap at 0.043″
- Iridium performance at a lower price point than ACDelco
- Less frequently mentioned in Trailblazer-specific owner forums than ACDelco or NGK
Champion Platinum RE10PMC5 Spark Plug
Champion’s platinum-tipped direct-fit plug for the 2002-2009 4.2L Trailblazer, also sold in a double-platinum version.
- Platinum-tipped electrode
- Direct fit for 2002-2009 4.2L L6
- Also available in Double Platinum
- Widely available at auto parts retailers as a full 6-plug set
- Platinum plugs typically don’t last as long as iridium under the same conditions
Buying tips
- The 4.2L Vortec I6 is known for being sensitive to off-spec plugs — misfires and rough idle are the most common symptom of the wrong choice, so stick to a direct-fit part rather than a close substitute.
- Gap matters as much as brand: confirm 0.040″-0.043″ at install even on pre-gapped plugs.
- This engine takes 6 plugs — buy a full set rather than mixing brands across cylinders.
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