Why do Honda Fits have 8 spark plugs?
Some Honda Fits use eight spark plugs because they employ a twin-spark arrangement—two plugs per cylinder on a four-cylinder engine—chosen to improve combustion, efficiency, and emissions in certain markets and generations. Not all Fits use this setup.
Understanding twin-spark ignition
Twin-spark ignition means each cylinder has two spark plugs instead of one. The idea is to initiate combustion more reliably and quickly, especially under lean-burn strategies, cold starts, and variable loads. In practice, the system often uses separate ignition coils or coil packs for each plug and can fire the plugs simultaneously or in a controlled sequence to optimize the flame front and reduce misfires.
Why Honda chose it for some Fits
Honda introduced the eight-plug configuration on certain Jazz/Fit engines to meet stringent emissions standards and improve fuel efficiency in specific markets and model years. The setup is typically associated with a 1.5-liter four-cylinder family engine that uses advanced ignition control (often labeled as i-VTEC or similar) and may be tuned for lean-burn capable operation. Variants without twin-spark exist, so eight plugs are not a universal feature of every Fit.
How the eight plugs are arranged
In the twin-spark configuration, each of the four cylinders contains two spark plugs. Depending on the engine design, each plug may have its own ignition coil (coil-on-plug) or two plugs may share coil packs that fire in a coordinated manner. The dual-ignition setup can produce two simultaneous sparks within a cylinder or staggered sparks to optimize combustion timing, improving efficiency and reducing emissions.
Before we list the practical implications, here is a concise look at the main reasons manufacturers opt for this design.
- Improved combustion efficiency and stability across a wide range of operating conditions, including cold starts and lean-burn modes.
- Enhanced fuel economy and lower emissions due to more complete and faster ignition of the air-fuel mixture.
- Reduced misfires and smoother idle as cylinder-to-cylinder variations are mitigated by dual ignition.
- Better throttle response and performance in compact engines where the flame front propagation matters.
The eight-spark arrangement is typically found only on specific Fits; many other Fits use a traditional one-spark-per-cylinder setup, which is simpler and cheaper to service.
Maintenance considerations
Having two plugs per cylinder doubles the number of plugs that eventually wear out and may increase maintenance costs and service time. Replacement intervals depend on the plug type (copper, platinum, iridium) and Honda's recommendations for the engine code. When servicing a twin-spark Fit, technicians must ensure proper gap and torque for each plug and verify ignition coil function to prevent misfires. Always consult the owner’s manual or a Honda service bulletin for model-specific guidance.
Additionally, diagnostic codes for misfires may require checking each plug's condition on both plugs per cylinder, which can be more involved than a single-plug setup.
Bottom line
Eight spark plugs in a Honda Fit reflect a twin-spark approach used on certain engines to boost combustion efficiency and emissions performance. It's not a universal feature; buyers should verify the engine code and market-specific specs to know whether their Fit uses eight plugs. For owners with a twin-spark engine, following the recommended maintenance schedule and using the correct plug type is essential to preserve performance and reliability.
Summary
In some Honda Fits, eight spark plugs are used because the engine employs a twin-spark, dual-ignition system—two plugs per cylinder on a four-cylinder engine. This arrangement aims to improve combustion efficiency, start-up behavior, and emissions, particularly in markets with stricter standards. The setup is not universal, so check your model’s engine code to confirm whether eight plugs apply to your car.
