A cylinder 4 misfire in a 2017 Honda Fit (GK5) with the L15B1 engine can be caused by several issues, despite the common belief that loose spark plugs primarily affect older models. While spark plugs and coil packs are potential culprits, the notorious oil blow-by and carbon buildup issues in these engines often lead to clogged fuel injectors, directly contributing to misfires.
Common Causes of Cylinder 4 Misfire
Before diving into the more complex potential issues, it’s advisable to check the basics:
- Spark Plugs: Swap the spark plug from cylinder 4 with cylinder 1. If the misfire code follows the spark plug to cylinder 1, then faulty spark plugs are the likely cause. Replace them with recommended specifications.
- Coil Packs: Similarly, swap the coil pack from cylinder 4 with either cylinder 2 or 3. If the misfire code follows the coil pack, a replacement is needed. Hitachi coil packs are generally recommended for Honda vehicles.
Addressing the L15B1’s Underlying Issues: Oil Blow-by and Carbon Buildup
Even if swapping spark plugs and coil packs doesn’t resolve the misfire, the root cause in many L15B1 engines often lies in excessive oil blow-by and subsequent carbon buildup:
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Clogged Fuel Injectors: Oil blow-by introduces oil vapor into the intake manifold, which mixes with carbon deposits and eventually clogs the fuel injectors, especially in cylinder 4.
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Walnut Blasting: A walnut blast cleaning of the intake valves is a highly recommended procedure to remove carbon buildup. Although valve adjustment is optional, it’s beneficial to perform it while the intake is disassembled.
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Fuel Injector Cleaning or Replacement: Cleaning or replacing the fuel injectors is crucial for restoring proper fuel delivery. Sending them for professional cleaning is a cost-effective option.
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High-Pressure Fuel Pump Feed Pipe: Critically, the high-pressure fuel pump’s feed pipe on the L15B1 is a known weak point. It’s a one-time use part prone to leaks, potentially causing fires. Replacing this pipe is non-negotiable during this repair process.
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Oil Catch Can: Installing an oil catch can helps mitigate future oil blow-by by trapping oil vapor before it enters the intake manifold, significantly reducing carbon buildup and preventing recurring misfires.
Conclusion: Long-Term Solution for Cylinder 4 Misfire
While checking spark plugs and coil packs is a good starting point, addressing the inherent oil blow-by and carbon buildup issues in the L15B1 engine through walnut blasting, fuel injector cleaning or replacement, and especially replacing the high-pressure fuel pump feed pipe, offers a more comprehensive and lasting solution to cylinder 4 misfires. Implementing an oil catch can as a preventative measure will prolong engine health and minimize future occurrences of this problem.
