UF303 Coil & Iridium Plug Set: The Smart Upgrade for GM 4.2L Engines
If you own a Chevy Trailblazer, GMC Canyon, or any GM vehicle with the 4.2L inline-6, you know the telltale signs of coil failure—rough idle, misfires, and reduced fuel economy. This UF303 ignition coil and 5019 double iridium spark plug set is a direct replacement for the factory C1395, offering a complete tune-up solution in one package. Before you buy, understand what makes this set a compelling choice and what to check to ensure it fits your specific model.
Key Considerations Before Buying
- Vehicle compatibility is critical: This set fits a wide range of GM vehicles, but always confirm your exact engine size (I-6 4.2L) and year. The included 5019 plugs are designed for this engine, but cross-check your owner's manual or use an online fitment tool.
- Double iridium plugs offer longer life and better performance: The 5019 plugs feature iridium on both center and ground electrodes, which means they can last up to 80,000 miles, reducing maintenance frequency. This is a significant upgrade over standard copper or platinum plugs.
- Replacing coils and plugs together is cost-effective: If you're experiencing misfires, it's often wise to replace both coils and plugs at the same time to avoid future issues. This set provides all six of each, saving you the hassle of sourcing parts separately.
What Our Analysts Recommend
When evaluating this set, look for OEM-grade construction: the coil should have a robust housing and a sealed connector to prevent moisture ingress, a common failure point. For the plugs, verify the iridium tip quality and the exact heat range to match your engine's requirements. Genuine parts will have clear laser-etched part numbers and a consistent gap out of the box.
Coils Market Context
Market Overview
The aftermarket ignition coil and spark plug market is vast, with options ranging from budget to premium. For GM 4.2L engines, a failing coil is a common issue, and many owners seek reliable replacements. This set sits in the mid-to-premium tier, combining two critical components in one convenient package, which is a growing trend for DIYers and professional mechanics alike.
Common Issues
The most common problems with ignition coils in this engine family include cracking of the coil housing due to heat, and internal short circuits that cause misfires. Spark plug issues typically manifest as fouling or electrode wear, leading to poor combustion. Choosing a set with double iridium plugs addresses wear, but you must also ensure the coil's thermal protection is adequate.
Quality Indicators
High-quality coils are often 'E-coated' or have a corrosion-resistant finish, and the connector pins are solid, not flimsy. For plugs, look for a fine-wire iridium center electrode (typically 0.4mm) and a tapered ground electrode for better flame propagation. Brand reputation and warranty also serve as quality signals—OEM-equivalent parts often carry a 1-2 year warranty.
Review Authenticity Insights
Grade B Interpretation
The B grade and 10.00% estimated fake review percentage suggest that while the vast majority of the 3,242 reviews are authentic, a small fraction may be incentivized or overly promotional. This is not alarming, especially given the high volume of genuine feedback. A 10% rate is within a manageable range for a popular product, and the core sentiment is reliable.
Trust Recommendation
You can trust the overall 4.89-star rating, but be aware that the adjusted rating of 4.60 is more realistic. Pay close attention to reviews that mention specific vehicle models and detailed installation experiences—these are the most credible. Given the authenticity, you can proceed with confidence, but always cross-check the fitment for your exact vehicle.
Tips for Reading Reviews
When reading reviews, filter for those that include photos or videos of the installation, as they often reveal the part's build quality. Also, look for comments about long-term durability (after 6 months or 10,000 miles) and any issues with misfires after installation. Be wary of reviews that are overly brief or use generic praise like 'great product' without specifics.
Expert Perspective
Based on the analysis, this UF303 coil and 5019 plug set is a well-received, reliable solution for GM 4.2L owners. The high rating and genuine reviews indicate that it effectively resolves common misfire issues. The combination of coils and plugs in one set is a smart approach, ensuring that all components are fresh and compatible. The 10% fake review rate is a minor concern, but the substantial authentic feedback outweighs it.
Purchase Considerations
Before purchasing, verify your vehicle's year and engine size—this set is not for V8 models. Consider your mechanical skill level; installation is straightforward (remove the coil bolt, pull the coil, replace the plug, and reinstall), but if you're not comfortable, factor in labor costs. Also, compare the price against buying OEM coils and plugs separately—while this set may be cheaper, ensure the quality meets your expectations.
Comparing Alternatives
Shoppers should compare this set with other aftermarket options like Denso or ACDelco, which are original equipment for many GM vehicles. While this set offers value, some may prefer to stick with OEM for piece of mind, especially if your vehicle is still under warranty.
