Modern automotive ignition systems use coil packs for every cylinder, shortening wire runs, increasing spark energy, and improving timing. However, coil-on-plug ignition systems, with their short or non-existent wires, have rendered some proven spark plug tests obsolete. It’s easy to test for spark, but Thexton’s 458 plug tester can also tell you how strong a spark you’re getting.
The tester has an adjustable gap between the anode and cathode, and since air’s electrical resistance is nearly constant, adjusting the gap can give a mechanic a good qualitative picture of a voltage’s magnitude. The 458 is adjustable from 0V to 40,000V, which, while lower than the spark energies of many common COP systems (for instance, GM’s LS engines have 55,000V packs), is more than enough to ignite a good fuel/air mixture.
Though spark technology has evolved, the tools haven’t gotten much more expensive. The Thexton is available from ToolSource.com for just under $19 before shipping. As an added bonus, it looks like it’ll work with distributor-based and wasted-spark ignition systems as well.
Thexton 458 [Tool Source]