A Guide to Replacing Spark Plugs on Your 2003-2008 Infiniti G35
Choosing the right spark plugs for your G35 is critical for performance and avoiding future headaches.
- Stick with NGK or Denso branded spark plugs; they are the OEM suppliers and are proven to work best.
- Before you buy, check for oil in the spark plug wells. Oil indicates a leaking valve cover gasket that must be replaced.
- Verify your engine type. 2007-2008 G35 sedans (VQ35HR) use different plugs than earlier models (VQ35DE).
- If replacing plugs yourself, carefully label the coil pack connectors to prevent mixing them up on reinstallation.
Is It Time for New Spark Plugs?
Infiniti recommends replacing the original spark plugs around 105,000 miles, but you might need to do it sooner. If your G35 is showing any of these signs, your spark plugs could be the culprit.
Common Symptoms of Bad Spark Plugs:
- Rough Idling: The engine feels shaky or uneven when you're stopped.
- Poor Acceleration: The car feels sluggish or slow to respond when you press the gas pedal.
- Worse Fuel Economy: You're filling up your gas tank more often than you used to.
- Engine Misfires: You might feel a hesitation or stumble from the engine while driving.
- Check Engine Light: A failing spark plug can trigger the check engine light, often showing codes like P0300 (random misfire) or P0301 through P0306 for a specific cylinder.
A Common G35 Problem: Oil in Spark Plug Wells
A very common issue on the G35 is for the valve cover gaskets to leak oil into the spark plug tubes. When you pull out the ignition coil, if you see oil on it or in the tube, you have this problem. This oil can ruin the new spark plug and coil, causing a misfire. The only fix is to replace the valve cover and its integrated seals. This should be done before or at the same time as your spark plug change.
Choosing the Right Aftermarket Spark Plugs
When it comes to spark plugs for the Infiniti G35, brand choice matters. The original factory plugs are made by NGK or Denso. For the best results and to avoid problems, it is strongly recommended you stick with these two brands.
Brand Tiers for Your G35:
- Tier 1 (Recommended): NGK & Denso. These are the original equipment (OEM) manufacturers. Choosing their Iridium or Platinum aftermarket plugs is the safest bet for compatibility and long life. Many owners report that NGK Laser Platinum or Iridium IX plugs work perfectly.
- Tier 2 (Use with Caution): Bosch, Champion. While these are established brands, G35s can be picky. Some owners have reported rough idling and misfires after installing Bosch plugs, only to have the problem disappear when they switched back to NGK. It's generally best to avoid them for this car.
- Tier 3 (Not Recommended): Unfamiliar or budget brands. Given the importance of the spark plugs and the labor involved in changing them, saving a few dollars on an unknown brand is not worth the risk of poor performance or premature failure.
Know Your Engine: VQ35DE vs. VQ35HR
The 2003-2008 G35 used two different engines, and they take different spark plugs. Ordering the wrong part is a common mistake.
- VQ35DE Engine: Found in 2003-2006 Sedans and 2003-2007 Coupes. It typically uses NGK PLFR5A-11 plugs.
- VQ35HR Engine: Found in 2007-2008 Sedans. This engine uses a different plug, such as a DENSO FXE22HR11.
Always verify the correct part number for your specific year and model before purchasing.
How Much Does a Spark Plug Replacement Cost?
The cost can vary greatly depending on whether you do it yourself and if you need to replace the valve covers due to oil leaks.
| Item | Estimated Cost |
|---|---|
| Aftermarket Spark Plugs (Set of 6) | $25 - $180 |
| Shop Labor (Plugs Only) | $220 - $322 |
| Shop Labor (Plugs & Valve Covers) | $800 - $1200+ |
Frequently Asked Questions (FAQ)
Can I replace the spark plugs myself?
Yes, this is a DIY-friendly job for someone with moderate mechanical experience. You will need a good socket set with extensions, a 5/8" spark plug socket, and a torque wrench. The biggest challenge is reaching the cylinders closest to the firewall. It's critical to label the ignition coil connectors so you don't mix them up during reinstallation, which can cause a P0300 misfire code.
What are Iridium and Platinum spark plugs?
Iridium and platinum are precious metals used on the tip of the spark plug. They are much more durable than standard copper, allowing the spark plug to last for 100,000 miles or more. They also provide a more consistent spark over their lifespan. Your G35 came with platinum or iridium plugs from the factory, and you should use the same type for replacement.
Do I need to gap the new spark plugs?
Most of the time, no. High-quality NGK and Denso iridium or platinum plugs typically come pre-gapped from the factory for your specific vehicle. It's a good idea to double-check one or two plugs in the box to ensure they weren't damaged in shipping, but you should not try to adjust the gap on a fine-wire iridium plug, as you can easily break the delicate electrode.
What is a P0300 Random Misfire code?
The P0300 code means the engine's computer has detected a misfire, but it can't pinpoint it to a single cylinder. While this can be caused by worn-out spark plugs, it can also be caused by bad ignition coils, vacuum leaks, or even swapping the ignition coil wiring harnesses during a spark plug change.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22401-PLFR5A-11 22401-JK01D
The VQ35DE engine (2003-2007 Coupes, 2003-2006 Sedans) typically uses NGK Laser Platinum PLFR5A-11 plugs. The VQ35HR engine (2007-2008 Sedans) uses a different plug, such as the Denso FXE22HR11. Both are long-life iridium or platinum plugs. Torque specification is approximately 18-20 ft-lbs.
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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 G35:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Is It Time for New Spark Plugs?
- Common Symptoms of Bad Spark Plugs:
- A Common G35 Problem: Oil in Spark Plug Wells
- Choosing the Right Aftermarket Spark Plugs
- Brand Tiers for Your G35:
- Know Your Engine: VQ35DE vs. VQ35HR
- How Much Does a Spark Plug Replacement Cost?
- Frequently Asked Questions (FAQ)
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