Denso 5391 Spark Plug

Denso Iridium Power Spark Plug 5391

Denso Iridium Power spark plug 5391 is built for drivers who want precise ignition performance from a compact iridium design. It uses a 0.4 mm iridium center electrode, a copper core, and a nickel ground electrode to support consistent spark delivery in demanding secondary ignition systems.

Key Features

• Iridium center electrode tip with a 0.4 mm fine-wire design
• Tapercut and U-groove ground electrode tip design for focused spark exposure
• 5000 ohm resistance for controlled ignition circuit performance
• 0.8 mm pre-gap size for OE-style setup reference
• 14.00 mm thread diameter, 19.00 mm reach, and flat seat type
• 20.6 mm hex size for proper socket fitment
• Manufacturer heat range 24

Product Details

The Denso Iridium Power line is engineered around a fine iridium center electrode to reduce the firing surface at the spark point. That smaller electrode profile helps concentrate the spark, while the tapercut and U-groove ground design supports efficient flame initiation. Part number 5391 is a practical choice for ignition service where stable spark quality and OE-style dimensions matter. This part cross-references DENSO Auto Parts (e.g., IWM24) for the same application.

For shoppers searching for Denso 5391 spark plug replacement, Denso Iridium Power 5391, or an iridium spark plug for secondary ignition service, this part is built to match common 14 mm, flat-seat applications. It is also a relevant search for Honda Civic spark plug replacement and Toyota Corolla spark plug replacement when verifying engine-specific requirements.

What It Helps Address

• Hard starting caused by worn or weakened spark plugs
• Misfire conditions related to degraded ignition performance
• Rough idle from inconsistent spark delivery
• Reduced throttle response from aged secondary ignition components
• Service intervals where the original plug shows electrode wear

Installation Notes

Verify thread diameter, reach, seat type, hex size, and heat range against the engine specification before installation. Confirm the pre-gap setting matches the vehicle requirement, and inspect the ignition coil, plug wires, and cylinder head threads during service. For fitment-based searches, use the vehicle application details for the exact year, make, model, and engine combination before ordering a Denso 5391 spark plug.

Quality Assurance

Denso manufactures the Iridium Power line with a focus on precise electrode construction and consistent ignition performance. The fine iridium tip and OE-style dimensions support dependable service in properly matched applications.