Ignition spark tester - Page 1
Forum section: electronics / projects

author: antenna
author_rank: Frequent Contributor
timestamp: December 20, 2022, 05:30:26 am
content: I have a snowmobile that cuts out randomly when revving the motor and I would like to test for spark while running to see if it is electrical or fuel. I don't own a tester, and will buy one next time I am in town, but for the time being, would it work to solder a 1" square foil to one leg of a neon and a needle to the other leg and just stick the needle in the boot letting the capacitance of the other leg-foil complete the circuit? I saw Jerri Ellsworth do something similar with a loop antenna so I figured this would get me out of finding a high voltage resistor and using a ground clamp.

author: jonpaul
author_rank: Super Contributor
timestamp: December 20, 2022, 01:58:42 pm
content: NE2 or any small neon pilot lamp on a wood or plastic rod.Jon

author: Stray Electron
author_rank: Super Contributor
timestamp: December 20, 2022, 02:13:20 pm
content: The most effective ignition tester that I ever saw was when a friend's motorcycle died. Another "friend", a mechanic, pulled the ignition wire off of the spark plug and then stuck a metal key in it and had the owner hold the key while the mechanic kick the engine over. Nothing happened. Then the mechanic pulled the ignition wire off of my motorcycle and repeated the experiment. Needless to say, this time the owner found out how ignitions systems are supposed to work!Another of those "Good judgement comes from experience, and experience comes from bad judgement!" moments.

author: TheMG
author_rank: Frequent Contributor
timestamp: December 21, 2022, 02:18:23 am
content: You would typically connect the neon indicator inserieswith the spark plug, that's how those neon indicator based spark testers work.Your idea of capacitive coupling the neon may or may not work, but most importantly this method will only tell you that the ignition coil / magneto is outputting high voltage, not that the spark plug is actually firing, thus wiring the neon in series will produce more useful results, as it theoretically shouldn't light if the spark plug doesn't arc (such as would be the case under high compression with a weak ignition coil or too large a gap).

author: antenna
author_rank: Frequent Contributor
timestamp: December 21, 2022, 04:32:10 am
content: OK, I will wire it in series. Thanks!

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2022, 05:31:18 am
content: You can also use an air gap. We had a spark tester that was just a couple of electrodes stuck through the sides of a piece of acrylic with a wooden handle on it at my middle school shop class. We had a unit where we tore down a small engine and put it back together, back when they still taught useful skills like that in school.

author: jonpaul
author_rank: Super Contributor
timestamp: December 21, 2022, 01:10:21 pm
content: Please Do not put NE2 in series, un needed and the neon may blow or break.The E filed of a 20 kV HV ring pulse (ignition couil) is like a Tesla or Induction coil.Utilities commonly detect live wires with a hot stick, a long plastic rod with neon bulb, just bring the bulb near the wire or contact glass of lamp t wire.The HV E field is more that enough to ionozet the neon. You can then check all wires, plus without any unplugging or reconnectiosn.Many old tools electricians like screwdrivers had a neon embedded in the handle. ONE lead went to the screwdriver blade.Jon

author: Cramer
author_rank: Newbie
timestamp: December 21, 2022, 05:25:21 pm
content: As an ex auto mechanic, you can use a simple ohm meter to check a spark plug. Good readings are around 4-8 ohms. Above that the plug maybe breaking down.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2022, 05:39:36 pm
content: If you have an old style timing light with inductive clamp pickoff, it can be used as is to detect if the spark is present, but it will not tell you anything about the condition of the spark plug.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 21, 2022, 05:44:19 pm
content: I posted about my street bike developing an miss. What a pain in the ass.https://www.eevblog.com/forum/repair/motorcycle-woes/msg3026092/#msg3026092Quote from: Cramer on December 21, 2022, 05:25:21 pmPlugs I use in my bike are going to be >1kohm from the center electrode to the terminal. Terminal to ground electrode will be several megs. If it breaks down, over the insulator I will see the etch marks in the insulator. Wires I use will be in the 200ish ohms.Say 10,000 RPM or 167 revs per second, 3 cylinders, what do you think you will see? Consider also that the ignition will be dependent on the mixture, pressure, gap..... Spinning the motor with the plug in ambient pressures doesn't tell you much besides it's doing something. Better to test them under load. Scope would be a better choice for this.

author: vidarr
author_rank: Frequent Contributor
timestamp: December 21, 2022, 05:51:49 pm
content: Unscrew the plug. Leave the wire on. Turn the key. There will either be spark at the plug, or no spark. If no spark, unplug the wire from the distributor, hold it close to the distributor post, turn the key and see if you get a spark from the post to the wire. If you get a spark there, then your wire is bad. If no spark, but your engine turns over, you need to move on to the distributor. This is just basic, generic methods, and can very with your vehicle.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2022, 06:21:27 pm
content: The point of a spark tester is that it goes in series with the plug so you can tell if the plug is actually firing. The breakdown voltage varies depending on cylinder conditions.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 21, 2022, 06:29:16 pm
content: You could short the plug and the indicator would still show something assuming there are no other problems. Similar to looking at the plug in air. You can tell something is happening but that's about it.

author: bdunham7
author_rank: Super Contributor
timestamp: December 21, 2022, 06:29:39 pm
content: Quote from: james_s on December 21, 2022, 06:21:27 pmNot quite--if the plug is breaking down internally or is fouled, you'll still get a spark on the tester. Sometimes that gap of the tester will actually improve the operation of the spark plug.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 21, 2022, 06:33:38 pm
content: Quote from: bdunham7 on December 21, 2022, 06:29:39 pmTrue in some cases. Adding more gap will increase the breakdown voltage. Harder on the ignition system. Here is a vintage spark plug with an internal, adjustable gap.

author: TheMG
author_rank: Frequent Contributor
timestamp: December 22, 2022, 01:39:17 am
content: Quote from: jonpaul on December 21, 2022, 01:10:21 pmNo it won't. There is not sufficient energy coming out of the ignition coil to damage the neon. We're talking about very short high voltage pulses at a relatively low current.Many spark testers commercially available are just that - a neon lamp with some wires and connectors to allow you to easily connect it to a spark plug. They've been making these things for decades.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 22, 2022, 10:59:13 am
content: Peak spark currents are in the 10-30mA rangeThere are commercial "Coil-on-Plug" pickups that are massively overpriced. They work as current transformers.. I think snapon etc make an expensive clamp on current transformers for engine analysers.I'd take the coil out of a small relay and pass the HT lead through it. You should pick up a healthy signal a basic opamp +ledYou could use a window comparator of some sort (555?) to see if the plug is actually sparking. If theres HT but no spark the current will be much lower, for a shorted plug the current will be higher I think.Some one out there might want to elaborate.