Various spark plug failures, including internal resistor faults, insulator damage, and electrode loss, lead to significant engine performance issues.
These failures manifest as misfiring, rough engine operation, power loss, or severe preignition events, sometimes causing collateral damage to engine components or other ignition system parts like magnetos.
Abnormal spark plug resistance, whether excessively high or non-existent, is a recurrent cause of engine stumbling and rough operation, underscoring the need for proper diagnostic testing.
The pilot noticed a high EGT reading. A magneto check revealed one of the eight spark plugs was not firing. Examination revealed resistance in five of the eight plugs exceeded the 2 MΩ limit. The internal resistors had failed and the current path was open. The resistors should have been about 1.5 kΩ.
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