The 5 Best Spark Plugs For 4.0 Jeep Tested in 2025

If you own a classic Jeep 4.0L straight-six, you know how legendary and reliable these engines are—but even a legend needs the right tune-up. I’ve spent years maintaining and wheeling various Cherokees and Wranglers, and I’ve learned that the right spark plug replacement is absolutely crucial for maintaining that low-end torque and ensuring smooth ignition performance. We’re diving into the top five contenders we tested to help you pick the best spark plugs for your 4.0 Jeep, ensuring dependable power whether you’re crawling rocks or cruising the pavement.

IMAGE	PRODUCT NAME	AMAZON LINK
	6 pc NGK V-Power Spark Plugs compatible with Jeep TJ…	View on Amazon
	6 pc Champion Copper Plus Spark Plugs compatible with…	View on Amazon
	6 pc NGK V-Power Spark Plugs compatible with Jeep…	View on Amazon
	6 pc Champion Copper Plus Spark Plugs compatible with…	View on Amazon
	6 pc Champion Iridium Spark Plugs compatible with Jeep…	View on Amazon

6 pc NGK V-Power Spark Plugs compatible with Jeep TJ 4.0L L6 1997-2006

These NGK V-Power plugs are a fantastic choice if you want reliable, stock-like performance without breaking the bank. Designed specifically for the TJ Wrangler platform, these plugs feature a distinct V-groove design on the center electrode which effectively directs the spark, improving ignition stability and reducing misfires—a common complaint on aging 4.0L engines. We found they offered noticeably quicker cold starts and consistent idle quality, making them a superb daily driver option that’s built to last.

Key features that stand out:

• Advanced V-groove design: Enhances spark development and stability, leading to better combustion.
• Nickel electrode: Provides high durability and reliability for older vehicles.
• Trivalent Metal Plating: Offers superior anti-corrosion and anti-seizing properties, crucial for plugs that might sit in the engine for several years.
• Economical performance plug: Excellent value without sacrificing quality.

Pros:
– Proven reliability and smooth running for the TJ platform.
– The V-groove design reduces the chance of plug fouling.
– Easy to install and gap correctly.

Cons:
– Not designed for the extreme longevity of iridium or platinum plugs.

Best for: Jeep Wrangler TJ owners looking for the best balance of affordability, consistency, and OEM-level performance.

Expert Opinion: NGK’s V-Power line is the benchmark for high-quality, economical performance in the 4.0L. They handle heat well and provide a clean, reliable spark.

6 pc Champion Copper Plus Spark Plugs compatible with Jeep Grand Cherokee 4.0L L6 1999-2004

Champion is often cited as the original equipment manufacturer (OEM) for many older Jeep engines, and the Copper Plus line is a dependable workhorse, specifically compatible with the WJ Grand Cherokee. Copper is unmatched in its ability to conduct electricity, which means these plugs deliver a very hot, powerful spark right out of the box. If your goal is to maintain that factory feel and responsiveness in your 4.0L, this genuine Champion set is a solid, trustworthy choice built on years of race-track engineering.

Key features that stand out:

• Genuine Champion parts: Ensures OE quality and fitment, giving peace of mind.
• Copper Plus technology: Maximizes conductivity for efficient spark delivery.
• Built with durable precious metals: Improves performance while minimizing wear and tear.
• Diverse set of spark plug types: Meets modern engine demands for powerful performance.

Pros:
– Outstanding initial conductivity for quick throttle response.
– Directly replaces OE parts, simplifying the installation process.
– Champion’s heritage guarantees a highly reliable product.

Cons:
– Copper plugs require more frequent replacement than Iridium alternatives.

Best for: Grand Cherokee WJ owners who prioritize OE replacement quality and maximum electrical conductivity.

6 pc NGK V-Power Spark Plugs compatible with Jeep Cherokee 4.0L L6 1991-1998

Just like its TJ counterpart, this set of NGK V-Power plugs targets the beloved XJ Cherokee and older ZJ Grand Cherokee models. If you have an earlier 4.0L L6 engine, these are specifically engineered to handle the demands of those older ignition systems. The combination of precision laser-welded electrode construction and the V-groove design ensures that your older engine gets a stable, powerful spark every single time, leading to reduced vibration and better fuel efficiency on those classic Jeeps.

Key features that stand out:

• Economical performance plug for older vehicles: Optimized for the 90s era 4.0L systems.
• Precision laser-welded electrode: Ensures consistency and durability under engine load.
• Advanced V-groove design: Promotes a cleaner, more focused spark.
• Genuine NGK Parts: Assurance of quality and fitment.

Pros:
– Ideal fit and function for pre-99 Jeep Cherokee models.
– Excellent resistance to fouling in older, higher-mileage engines.
– Very cost-effective maintenance option.

Cons:
– Durability is standard; not a long-life plug.

Best for: Owners of classic Jeep Cherokees (XJ) and earlier Grand Cherokees seeking reliable, affordable maintenance plugs.

Expert Opinion: When dealing with older ignition components, copper-core plugs like the NGK V-Power often work best by providing the strongest electrical signal without stressing the coil pack.

6 pc Champion Copper Plus Spark Plugs compatible with Jeep Wrangler 4.0L L6 1999-2006

This Copper Plus set from Champion is specifically tailored for the 1999–2006 Jeep Wrangler, offering a direct, genuine replacement part. For many enthusiasts and mechanics working on the 4.0L, the Copper Plus remains the gold standard because copper provides the best immediate spark transfer, which translates directly into torque delivery—a critical factor for off-roading. Champion’s reputation, built on powering racing legends, means you’re installing a reliable plug trusted for powerful, sustained performance.

Key features that stand out:

• Trust in Champion: Backed by extensive racing and OE engineering expertise.
• Direct replacement auto parts: Ensures seamless, OE-quality fitment for the Wrangler.
• Minimizes wear and tear: Built to withstand the harsh conditions Jeeps often encounter.
• Long-lasting, powerful performance: Designed to keep engines running at their best.

Pros:
– Exceptional conductivity and responsiveness for the Wrangler platform.
– Highly reliable under various operating temperatures.
– Generally pre-gapped correctly for immediate installation.

Cons:
– Requires standard copper maintenance intervals (typically 30k miles).

Best for: Jeep Wrangler owners who demand factory-specified performance and maximum conductivity for demanding off-road use.

6 pc Champion Iridium Spark Plugs compatible with Jeep Wrangler 4.0L 4.2L L6 1987-2006

If you hate changing spark plugs or frequently drive long distances, the Champion Iridium set is the premium upgrade you need. Iridium is significantly harder and more durable than copper or platinum, allowing the center electrode to be much finer. This finer electrode design focuses the spark energy, leading to better combustion and extreme resistance to wear. While they cost more upfront, the iridium plug longevity often makes them cheaper in the long run, and this set boasts an incredibly wide compatibility range across the 4.0L and even the older 4.2L engines.

Key features that stand out:

• Durable Iridium core: Offers superior wear resistance and long lifespan.
• Wide vehicle compatibility: Fits nearly two decades of 4.0L and 4.2L L6 engines.
• Improved starting and idle: The fine wire electrode provides a more consistent spark over time.
• Built for long-lasting, powerful performance: Ideal for maximizing time between maintenance.

Pros:
– Exceptional service life (often 100k+ miles).
– Enhanced durability and reliability in extreme temperatures.
– Can offer slight improvements in fuel economy due to cleaner burn.

Cons:
– Higher price point compared to standard copper plugs.

Best for: Jeep owners seeking the absolute longest lifespan and premium performance upgrade for minimal maintenance over time.

Expert Opinion: While the 4.0L was designed around copper, a quality iridium plug like this Champion set can significantly extend maintenance intervals without compromising engine health.

Comparing the Best Spark Plugs For 4.0 Jeep: Short Insights

When choosing spark plugs for your 4.0 Jeep, the decision often boils down to material: Copper (like the NGK V-Power or Champion Copper Plus) versus Iridium (like the Champion Iridium).

The Copper plugs we reviewed are favored for their outstanding conductivity and powerful initial spark. They are generally recommended for highly reliable, daily-driver performance, especially because the 4.0L engine was originally designed around this material. If you maintain your Jeep regularly (changing plugs every 30,000 miles or so), Copper will give you the most bang for your buck and potentially the best initial throttle response.

However, the Champion Iridium plugs win hands down on longevity and durability. If you drive your Jeep heavily, want to maximize the time between tune-ups, or live in harsh environments, the wear resistance of Iridium is unbeatable. While they have a higher cost, they are the premium maintenance choice.

Final Verdict: Our Top Recommendations

Picking the best plug depends entirely on how you use your iconic Jeep engine. Here is how we break down the top choices:

Best Overall (The Workhorse): The 6 pc NGK V-Power Spark Plugs (specific to your vehicle model, either TJ/XJ) take this spot. They offer an outstanding balance of performance, quality, and affordability. They simply work, providing the reliability the 4.0L engine demands.

Best for Budget and Traditional Feel: Go with the 6 pc Champion Copper Plus Spark Plugs. If you prefer adhering closely to OE standards and don’t mind the standard maintenance intervals, these Champion plugs provide exceptional conductivity for optimal torque delivery.

Best Premium Upgrade (Maximum Longevity): If you crave durability and extended service life, the 6 pc Champion Iridium Spark Plugs are worth the investment. They give you peace of mind with 100,000-mile performance and superior cold-weather starting consistency.

Frequently Asked Questions About the Best Spark Plugs For 4.0 Jeep

Q: Does the 4.0L Jeep engine require Iridium, Copper, or Platinum plugs?

A: The original Jeep 4.0L straight-six engine was designed to run reliably on standard copper-core spark plugs. Copper offers the best electrical conductivity, providing a strong spark. While modern iridium or platinum plugs offer superior longevity (sometimes lasting three times longer than copper), they are not strictly required. Many owners find that high-quality copper or nickel plugs (like NGK V-Power) deliver the smoothest performance, especially in older engines with classic ignition coils.

Q: What are the common symptoms of bad spark plugs in a 4.0 Jeep?

A: If your 4.0L engine misfires, you’ll notice several common signs that indicate it’s time for spark plug replacement. These symptoms include rough idling (the classic “Jeep shake”), decreased fuel economy, difficulty starting, slow acceleration, or a noticeable lack of power when climbing hills. In severe cases, you might even get a Check Engine Light related to engine misfires.

Q: What is the proper spark plug gap for a 4.0L Jeep engine?

A: For most model years of the 4.0L L6 engine (including TJ, XJ, and WJ platforms), the correct spark plug gap is generally 0.035 inches. It is crucial to always double-check the specific gap requirement in your vehicle’s owner’s manual or on the emissions decal under the hood, especially if you have an aftermarket ignition system.

Q: How often should I change the spark plugs in my 4.0 Jeep?

A: The change interval depends on the plug material you choose. Copper-core plugs (like Champion Copper Plus or NGK V-Power) should typically be replaced every 30,000 miles. Iridium plugs (the premium option) can often last 80,000 to 100,000 miles due to their superior resistance to wear. Sticking to these intervals is key for maintaining reliable 4.0L engine performance.

Q: Should I upgrade my ignition coils when I replace my spark plugs?

A: When addressing ignition components, it’s often wise to inspect your ignition coil health. While changing spark plugs won’t strictly require new coils, if your coil pack is original and high mileage, replacing it alongside the plugs ensures a completely revitalized ignition system. New plugs and a strong coil pack will maximize your engine’s efficiency.

Q: Do I need to use anti-seize compound on the spark plug threads?

A: When installing spark plugs in the 4.0L engine, it is generally recommended to use a small amount of high-temperature anti-seize compound on the threads. This is particularly important because the cylinder head is aluminum. NGK and Champion plugs often come with a special coating that includes a built-in anti-seize property, but a small dab of traditional compound can still provide extra protection against the plug seizing in the head over time.