I have one like this and another with an adjustable gap. They are invaluable not only for lawn equipment but work great on 2 stroke outboard motors. The thing I like is you can run a motor with one inline and see if a miss is because of spark lose.
Anyone ever used this spark plug tool?
- Thread starter Urshurak776
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I have used one of those on both a DIS and HEI ignition systems on vehicles and it showed spark in both instances.
All the time. Spark checker
4wd
$50 site donor 2026
Welders mirror (magnetic base) is another way to check for spark …
Pretty useful in the days of points and condensers. I’ve still got one.For lawn equipment only???
I can't be the only one around here who grew up around Prince Lucas's lightning bolt throwing ignition systems?IYKYK
To see if there is a spark at all, no load is best. Any resistive load on the secondary side causes the voltage to rise, and if the resistance is too high that high voltage has to go some place. So then if you don't like that cheapy deal, then use an inductive timing light, zero load for that test as well. A high resistive load is to have the secondary fire into the air, no grounded spark plug no nothin. And that can in some cases cause issues.
When you say load the ignition system, which side? Primary or secondary? Watch Pine Hollow Auto Diagnostics to see how to load the primary.
That tool is all about seeing it spark and nothing more.
I am well aware of how to test an ignition system, diagnostics is a large part of how I make a living. When you test for spark you are trying to see if the ignition system can ionize the spark plug gap. If the ignition system cant produce 25 thousand volts thats a no spark condition. That has been published in every GM service manual for no start testing from the beginnings of HEI to the 2025 Silverado I am posting a screenshot of. J-26792 is also known as an ST-125 tester because it takes 25 thousand volts to ionize the gap. An inline lightbulb type tester does not prove there is spark, it proves there is a couple volts to light a lightbulb.
For comparison, Ford uses an adjustable spark tester set to 25kv, Chrysler indicates to use a spark plug style spark tester which is what the J26792 is.
Most magneto systems won't produce 25kV, especially not on an initial pull start. Old Magneto and points systems produced much less. Even GM systems pre HEI were in the 18-20kV range. Old small engines could be much less than even 20kV.
You keep bringing up GM HEI, which stands for High Energy Ignition - ie higher than previous, and didn't exist until the early 70's As pointed out above lots of engines existed prior operating at much lower ignition voltages.
So back to this tool - very handy for small engines - and other magneto powered systems as pointed out above, where you just want to know if the system is firing.
I have one or two. I have used them a couple of times on OPE. But once OPE went away from points I seldom have ignition problems. It's almost always a carburetor.
Like someone mentioned 25K volts is not always needed. So with the mentioned test, you are guessing what the voltage is to ionize the gap?, since you think it needs 25K and no posted applied air pressure? and what size gap is that ? What you really need is a high voltage probe to check the exact voltage, and pretty standard stuff in the days of the CRT's. There is a reason older high power aircraft engines had .012 spark plug gaps. How much voltage to accomplish that? And what is the reason for doing such?
And that test like mentioned to see a spark is full of variables, applied air pressure, type of wires and or resistance, and most important the air gap to ionize. Your likely talking some old .045 up to .070 or so? Bigger gap more resistance requiring more volts from the coil.
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