NGK 3903 Spark Plug - Intake Side

NGK Iridium IX Spark Plug 3903 Overview

NGK Iridium IX Spark Plug 3903 is built for drivers who need precise ignition performance, stable combustion, and OE-style reliability. This spark plug uses an iridium center electrode, a nickel ground electrode, and a 5,000-ohm resistor to support consistent spark delivery across a wide range of older import and domestic applications.

The NGK Iridium IX Spark Plug line is known for fine-wire iridium construction and application-specific fitment. Part number 3903, also listed as BPR6EIX-11, is a direct replacement option for many vehicles including Honda Civic, Mitsubishi Mirage, and Nissan Sentra applications where the specified gap and heat range matter.

Key Features

• Iridium center electrode tip for focused spark delivery
• Copper core center electrode for heat transfer stability
• Nickel ground electrode with taper-cut tip design
• 5,000-ohm resistor for ignition noise suppression
• Flat seat design with 14 mm thread diameter
• Pre-gapped at .044 inches for many listed applications
• Manufacturer heat range 6
• NGK part number 3903 / BPR6EIX-11

Detailed Description

NGK 3903 is an Iridium IX spark plug engineered with a 13/16 hex, .75 reach, and non-removable nut terminal. The iridium tip helps maintain a consistent firing point, while the copper core supports thermal control under normal operating conditions. With a standard ground configuration and taper-cut ground electrode tip, this plug is built for dependable ignition performance in vehicles that call for a flat-seat, 14 mm spark plug.

Compatible With applications such as 1985-1987 Honda Civic, 1984-1987 Honda Prelude, 1987-1988 Nissan Sentra, 1990-1994 Mitsubishi Eclipse, and 1998-2000 Chevrolet Metro. It also appears in fitment for 1989-1998 Hyundai Sonata, 1989-1997 Geo Metro, and 1976-1987 Subaru Standard, making NGK 3903 a strong search match for older import spark plug replacement needs.

This part cross-references AMS Automotive 4709 and OSC 4217 for the same application.

What It Helps Address

• Hard starting caused by worn or inconsistent spark plugs
• Rough idle from weak ignition output
• Misfire conditions related to plug wear or incorrect gap
• Reduced throttle response from degraded combustion efficiency
• Ignition noise concerns in resistor-equipped systems

Installation Notes and Tips

Verify the vehicle’s required spark plug gap before installation. Many listed applications call for .044 inches, while some fitments specify .042 or .040 inches, so the gap should be checked and adjusted as needed. Confirm the correct heat range, thread diameter, reach, and seat type before installing NGK 3903.

For fitment-specific searches, this plug is commonly referenced for Honda Civic spark plug replacement, Mitsubishi Mirage ignition service, and Nissan Sentra tune-up applications. Always match the vehicle’s engine specification to the catalog listing before final installation.

Quality Assurance

NGK is a major OE spark plug supplier with decades of automotive manufacturing experience and broad coverage across domestic and import vehicle applications. Part number 3903 is produced to support original-equipment standards for durability and operational performance.