Denso 4129 Spark Plug

Denso U-Groove Spark Plug 4129 Overview

The Denso 4129 spark plug is part of the U-Groove Conventional line, built for drivers who want a straightforward ignition service part with OE-style construction. Its U-groove ground electrode design is engineered to improve ignitability, helping support more consistent combustion and engine efficiency.

For Honda Civic and Toyota Corolla maintenance, this Denso spark plug 4129 offers a practical replacement option with a copper center electrode core, nickel tip materials, and a standard single-ground configuration.

Key Features

• U-Groove conventional design for improved spark exposure at the gap
• Copper center electrode core material for dependable heat transfer
• Nickel center and ground electrode tip materials
• 5000 ohm resistance for ignition system noise control
• 0.9 pre-gap size for OE-style service replacement
• Flat seat, 14.00 mm thread diameter, and 19.00 mm reach
• 18.0 mm hex size for standard spark plug service tools
• Manufacturer heat range 27

Product Details

Denso U-Groove Conventional spark plugs are designed around a simple, serviceable ignition layout that focuses on reliable spark delivery. The U-shaped ground electrode helps expose the spark kernel more effectively than a basic flat-ground design, while the copper core supports thermal control during normal engine operation. The Denso 4129 is a conventional spark plug choice for routine tune-ups where OE-style dimensions and stable ignition performance matter. This part cross-references DENSO Auto Parts (e.g., U27FER9) for the same application.

Common Issues This Spark Plug Can Address

• Hard starting caused by worn or fouled spark plugs
• Rough idle from weak or inconsistent ignition
• Misfire symptoms related to degraded plug electrodes
• Reduced fuel efficiency from incomplete combustion
• Loss of throttle response during routine maintenance intervals

Installation Notes and Tips

Verify the thread diameter, reach, seat type, and hex size before installation to confirm the plug matches the cylinder head specification. Set the gap to the engine manufacturer’s requirement if adjustment is needed, and inspect ignition wires or coils during service to avoid repeat misfire concerns. For Honda Civic and Toyota Corolla applications, confirm the exact engine code and year before ordering the Denso 4129.

Quality Assurance

This spark plug is built by Denso, a recognized ignition component manufacturer, and follows the specifications listed for the U-Groove Conventional line. Use the published dimensions and heat range to match the correct service application.