Higher spikes indicate more resistance to spark. This can be due to a spark plug gap that is too narrow, a rich air-fuel mixture, or compression that is too low.

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Higher spikes in a spark plug trace typically indicate more difficulty for the spark to jump the gap, which could be due to a wide gap, lean air-fuel mixture, or high compression, not a narrow gap, rich mixture, or low compression.

Higher Spikes Indicate More Resistance to Spark