The list of approved maintenance items an aircraft owner can do under FAR Part 43 is long and includes replacing, cleaning and gapping plugs. In the spirit of cleaning, we think checking plug resistance is also on the list.
Like lowering your cholesterol and cutting back on salt intake, plug resistance wasn’t always a concern, or at least one that anyone bothered with. But with the widespread use of engine monitors that can detect the slightest combustion anomalies, spark plug resistance has become the latest fine-point maintenance item owners need to worry about.