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Denso 4221 Spark Plug
| Brand | Denso 4221 |
|---|---|
| Resistance | 5000 |
| Ground Electrode Tip Design | Standard |
| Ground Configuration | Standard |
| Ground Electrode Core Material | Nickel |
| Center Electrode Core Material | Copper |
| Center Electrode Tip Material | Nickel |
| Pre-Gap Size | 0.8 |
| Ground Electrode Quantity | 1 |
| Hex Size | 16.0 |
| Manufacturer Heat Range | 20 |
| Seat Type | Flat |
| Reach | 19.00 |
| Thread Diameter | 14.00 |
| Fits | —29 vehicles |
U-Groove design. Improves ignitability for more efficient engine performance.
Copper core. Helps promote consistent spark delivery and combustion.
Conventional spark plug. A straightforward secondary ignition replacement part.
Cross-references DENSO Auto Parts U20ESR-N for the same application. See all 1.
Denso 4221 Spark Plug Overview
Denso 4221 is a U-Groove conventional spark plug built for reliable ignition performance in secondary ignition systems. The U-groove electrode design helps improve ignitability, while the copper core and nickel electrode materials support consistent spark delivery for everyday driving and maintenance service.
For drivers searching for a Denso spark plug for Honda Civic, Toyota Corolla, or similar import applications, this part number 4221 offers a straightforward OE-style replacement with a 0.8 mm pre-gap, 14.0 mm thread diameter, 19.00 mm reach, and flat seat design.
Key Features
- Denso U-Groove Conventional spark plug for secondary ignition service
- U-groove electrode profile for improved ignitability and engine efficiency
- Copper center electrode core with nickel tip material
- Nickel ground electrode core material with standard ground configuration
- 5000 ohm resistance for ignition system noise control
- 0.8 mm pre-gap, 16.0 mm hex size, flat seat, 19.00 mm reach
- Manufacturer heat range 20 for specified engine applications
Product Details
The Denso U-Groove Conventional line is built around a practical spark plug design that focuses on stable combustion and dependable ignition performance. Part number 4221 uses a standard single-ground-electrode layout with nickel and copper construction, which supports consistent spark transfer and serviceable durability in the correct engine application. This Denso 4221 spark plug is a direct-fit style component for vehicles that call for the listed thread diameter, reach, seat type, and heat range.
This part cross-references DENSO Auto Parts (e.g., U20ESR-N) for the same application.
Common Issues This Part Can Address
- Hard starting caused by worn or inefficient spark plugs
- Rough idle from weak or inconsistent ignition output
- Misfire concerns related to aged secondary ignition components
- Reduced fuel efficiency from incomplete combustion
- Loss of throttle response from degraded spark plug performance
Installation Notes and Tips
Verify the engine calls for a 14.0 mm thread diameter, 19.00 mm reach, flat seat, and 0.8 mm pre-gap before installation. Check the ignition system condition, inspect plug wires or coil-on-plug components, and confirm the replacement matches the original heat range and resistance specification. For fitment-based searches, this Denso 4221 spark plug is commonly referenced for Honda Civic and Toyota Corolla service applications where the listed dimensions match the engine requirement.
Quality Assurance
Denso manufactures ignition components to OE-level dimensional and performance standards for specified applications. The U-Groove Conventional design is engineered to support reliable ignition and efficient combustion when installed in the correct vehicle application.
| Year | Make | Model | Notes |
|---|---|---|---|
| 2009 | Suzuki | LT-A750X KingQuad AXi 4x4 | U-Groove Conventional |
| 2008 | Arctic Cat | 700 EFI 4x4 Auto M4 | U-Groove Conventional |
| 2008 | Suzuki | LT-A750X KingQuad AXi 4x4 | U-Groove Conventional |
| 2007 | Arctic Cat | 700 EFI 4x4 Auto LE | U-Groove Conventional |
| 2007 | Suzuki | LT-A450X KingQuad AXi 4x4 | U-Groove Conventional |
| 2007 | Suzuki | LT-A500F Vinson 500 4x4 Auto | U-Groove Conventional |
| 2007 | Suzuki | LT-F500F Vinson 500 4x4 | U-Groove Conventional |
| 2006 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 2006 | Arctic Cat | 700 EFI 4x4 Auto SE | U-Groove Conventional |
| 2005 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 2004 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 2003 | Arctic Cat | 400 2x4 | U-Groove Conventional |
| 2003 | Arctic Cat | 400 4x4 | U-Groove Conventional |
| 2003 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 2003 | Suzuki | LT-F500F Vinson 500 4x4 | U-Groove Conventional |
| 2002 | Arctic Cat | 375 Auto 2x4 | U-Groove Conventional |
| 2002 | Arctic Cat | 375 Auto 4x4 | U-Groove Conventional |
| 2002 | Arctic Cat | 400 2x4 | U-Groove Conventional |
| 2002 | Arctic Cat | 400 4x4 | U-Groove Conventional |
| 2002 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 2001 | Arctic Cat | 400 2x4 | U-Groove Conventional |
| 2001 | Arctic Cat | 400 4x4 | U-Groove Conventional |
| 2001 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 2000 | Arctic Cat | 400 2x4 | U-Groove Conventional |
| 2000 | Arctic Cat | 400 4x4 | U-Groove Conventional |
| 2000 | Arctic Cat | 500 4x4 | U-Groove Conventional |
| 1999 | Arctic Cat | 400 2x4 | U-Groove Conventional |
| 1999 | Arctic Cat | 400 4x4 | U-Groove Conventional |
| 1999 | Arctic Cat | 500 4x4 | U-Groove Conventional |
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