Is there an objective DIY spark plug test?

[mattmro444]

When one reads spark plug reviews, people say the engine runs better with new plugs. While some of that could be due to better gap in new plugs, I'm afraid some of that is placebo, like better running engine after oil change.

Now, I understand that one can measure firing voltage via oscilloscope. Is there a simpler objective test?

Thanks
MRO Supply

[drew]

Over time the gap increases as the center and side wire electrodes erode. As this wear occurs the edges of the electrodes begin to round off. The larger radius on these components requires a higher voltage to bridge the gap.

Carbon is a very good conductor and build up on the center ceramic can complete the circuit between the shell and the center wire. This grounding can drive up the needed voltage as well. Worn plugs will typically affect starting, idle, and high rpm use.

The service life of a spark plug heavily depends on the the engine type and how it is used. My recommendation is to change the plugs at 10% less then the Mfg'ers recommended service interval. Only use the OEM plug and not some fad or special plug with so called special technology. IMO it is very hard to beat NGK, Denso (formerly Nippon Denso), Bosch and AC Delco.