Why a Cracked Spark Plug Cap Intermittently Kills Spark

A demonstration field guide for tracking across a cap after rain or wash using cap crack map and resistance before replacing the plug cap.

This demonstration guide answers one field question about tracking across a cap after rain or wash. Measurements come before parts, and the notes are not a generic equipment FAQ.

Diagnose before replacing parts

Start with cap crack map and resistance. That reading separates tracking across a cap after rain or wash from adjacent faults that share the same complaint.

If the measurement is out of spec, treat the plug cap as the primary path. If it is in spec, do not replace the plug cap just to complete a parts list.

Repair the failed system

The usual correction is the plug cap, installed to the documented spec for this complaint.

A demonstration shop records the finding so the next technician is not repeating a guess about tracking across a cap after rain or wash.

Stop before you make it worse

Do not filling a cracked cap with silicone. That shortcut hides the original measurement and creates a second failure.

If the machine still fails after the plug cap is corrected, convert the visit to a broader diagnosis rather than stacking parts.

Written and published by Ridgeline Small Engine.

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