Essential Guide to Spark Plugs for the 2002-2004 Infiniti I35
Keep your I35's V6 engine running strong by choosing the right spark plugs for the job.
- Stick with OEM-quality Iridium or Platinum spark plugs from brands like NGK and Denso for the best performance and longevity.
- Replacement of the three rear spark plugs is difficult, requiring the removal of the upper intake manifold.
- While replacing plugs, always inspect for oil in the spark plug tubes, which points to a leaking valve cover gasket that must also be fixed.
- The recommended service interval with high-quality plugs is approximately 100,000 miles.
Signs of Failing Spark Plugs in Your I35
When your spark plugs start to wear out, your car will usually let you know. Worn plugs can't create a strong enough spark, leading to incomplete fuel combustion. You might notice one or more of these symptoms:
- Rough Idle: The engine may shake or vibrate more than usual when you're stopped.
- Poor Acceleration: The car may feel sluggish or hesitate when you press the gas pedal.
- Reduced Fuel Economy: You may find yourself filling up the gas tank more often. Worn plugs can decrease fuel economy by as much as 30%.
- Engine Misfires: You might feel a jerking or stumbling from the engine while driving.
- Check Engine Light: A failing spark plug is a common reason for the check engine light to come on. You'll often see codes like P0300 (random misfire) or P0301 through P0306 for specific cylinders. 🎬 Watch: How to diagnose and repair a cylinder misfire code
A Note on a Related Issue: Leaking Valve Cover Gaskets
The VQ35DE engine in the I35 is known for valve cover gaskets that can leak oil directly into the spark plug tubes. This oil will ruin both the spark plug and the ignition coil, causing a misfire. When you replace your spark plugs, it is critical to check the tubes for any signs of oil. If oil is present, you must replace the valve cover gaskets to prevent the new plugs and coils from failing again.
🎬 See this walkthrough for replacing valve cover gaskets and plugsChoosing the Best Aftermarket Spark Plugs
For the Infiniti I35, the quality of your spark plugs matters. The VQ35DE engine was designed to use long-life platinum or iridium spark plugs. Using cheaper, standard copper plugs is not recommended as they will wear out very quickly and can cause performance issues.
When shopping for aftermarket plugs, sticking close to the Original Equipment (OE) design is your best bet for a trouble-free experience. The original plugs were made by NGK, and both NGK and Denso are highly recommended aftermarket brands that supply parts directly to Infiniti and other Japanese automakers.
Aftermarket Spark Plug Brand Tiers for Infiniti I35
| Tier | Brands | Description & Notes |
|---|---|---|
| Top Tier (OEM Quality) | NGK, Denso | Both NGK and Denso are OEM suppliers for Infiniti. Their Iridium and Double Platinum plugs (like the NGK Laser Platinum or Denso Iridium Long-Life) offer the best performance and lifespan, often lasting 100,000 miles. These are the most recommended choice. |
| Mid Tier (Quality Alternative) | Bosch | Bosch offers quality Double Iridium and Double Platinum plugs that are a good alternative to OEM. They are designed for long life and consistent performance, making them a reliable choice. |
| Economy Tier | Autolite, Champion | These brands provide budget-friendly options like the Autolite Iridium XP or Champion Double Platinum Power. They can work well but may not offer the same extended service life as the top-tier brands. |
Important Installation Note: The Rear Spark Plugs
Replacing the spark plugs on the I35's V6 engine is more difficult than on many other cars. The front three spark plugs (cylinders 2, 4, 6) are easy to access. However, the rear three plugs (cylinders 1, 3, 5) are located underneath the upper intake manifold. This manifold must be removed to reach them, which makes the job much more complex and time-consuming. If you or your mechanic remove the manifold, it is essential to replace the intake manifold gasket at the same time to prevent air leaks.
🎬 Watch: How to replace rear plugs and the intake gasketFrequently Asked Questions (FAQ)
How often should I change the spark plugs on my I35?
If you use high-quality Iridium or Platinum spark plugs, the recommended replacement interval is every 100,000 miles. However, if you notice any failure symptoms, you should inspect them sooner.
What is the correct spark plug gap for the 2002-2004 Infiniti I35?
Most of the recommended Iridium and Platinum spark plugs for the I35 come pre-gapped from the factory (usually at 0.044 inches or 1.1mm). It is not recommended to adjust the gap on these fine-wire plugs as you can easily damage the delicate electrode. Always verify the part is listed for your vehicle.
Should I use anti-seize on the new spark plug threads?
Major manufacturers like NGK advise against using anti-seize on their modern spark plugs. The plugs have a special metal plating that acts as an anti-seize and prevents corrosion. Adding more lubricant can cause you to over-tighten the plug, which can damage the plug or your engine's cylinder head.
Should I replace the ignition coils at the same time as the spark plugs?
You don't have to replace the ignition coils if they are working correctly. However, since replacing the rear spark plugs requires significant labor to remove the intake manifold, many owners choose to replace the rear ignition coils at the same time as a preventative measure. This is especially true if the car has high mileage or if you find oil in the spark plug tubes.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22401-5M015 22401-5M016 PLFR5A-11 PLFR6A-11
Engine: 3.5L V6 (VQ35DE) Plug Type: Iridium or Platinum Gap: 1.1mm (0.044 in), typically pre-set Quantity Needed: 6
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Infiniti I35:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Signs of Failing Spark Plugs in Your I35
- A Note on a Related Issue: Leaking Valve Cover Gaskets
- Choosing the Best Aftermarket Spark Plugs
- Aftermarket Spark Plug Brand Tiers for Infiniti I35
- Important Installation Note: The Rear Spark Plugs
- Frequently Asked Questions (FAQ)
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