Denso 3129 Spark Plug

Denso 3129 U-Groove Spark Plug for Toyota and Geo

Denso 3129 is a conventional spark plug built for direct ignition service in select Toyota and Geo applications. Its U-groove ground electrode design is engineered to improve ignitability, helping support more efficient combustion and steady engine operation.

Key Features

• U-Groove ground electrode tip design for improved spark exposure
• Nickel ground electrode tip with nickel ground core material
• Copper center electrode core material for reliable conductivity
• 5000 ohm resistor design for ignition noise suppression
• Pre-gapped to 0.8 mm
• Flat seat, 14.00 mm thread diameter, 19.00 mm reach, 16.0 mm hex size
• Manufacturer heat range 16

Product Details

This Denso U-Groove Conventional spark plug is part number 3129 and cross-references Denso Auto Parts Q16R-U for the same application. It is built for select 1988-1993 Toyota Celica, Corolla, 4Runner, and Pickup models, plus 1990-1992 Geo Prizm applications. The U-Groove design increases the spark path exposure at the ground electrode, which supports more consistent ignitability and efficient engine operation in the specified vehicles.

The Denso U-Groove Conventional line focuses on dependable OE-style ignition performance with a straightforward conventional plug design. For drivers servicing older Toyota and Geo engines, Denso 3129 provides the electrode materials, resistor value, and factory-style dimensions needed for proper secondary ignition service.

Vehicle Fitment

• Fits 1989-1993 Toyota Celica, N/A, U-Groove Conventional
• Fits 1990-1992 Geo Prizm, N/A, OE; Spark Plug - U-Groove Conventional
• Fits 1990-1992 Toyota Corolla, N/A, U-Groove Conventional
• Fits 1988 Toyota Corolla, N/A, U-Groove Conventional
• Fits 1988 Toyota 4Runner, N/A, U-Groove Conventional
• Fits 1988 Toyota Pickup, N/A, U-Groove Conventional

Common Service Uses

• Replacing worn spark plugs that can cause rough idle
• Addressing hard starting in older Toyota and Geo engines
• Restoring ignition consistency after plug wear or fouling
• Helping reduce misfire symptoms tied to degraded secondary ignition parts
• Supporting smoother combustion in specified Celica, Corolla, 4Runner, Pickup, and Prizm applications

Installation Notes and Quality Assurance

Verify thread diameter, reach, seat type, and heat range before installation to confirm the plug matches the engine specification. Check and set the gap to the required service specification if needed, and inspect ignition wires, distributor components, and coil condition during replacement. Denso manufactures this plug with OE-style dimensions and materials for the listed applications.