A great tool like the HEI spark tester (OTC 6589 Electronic Ignition Spark Tester) is no good to you if you don't know how to use it or read its results. To really take advantage of the spark tester you need to know the theory of how it works. Here's a basic summary:
The HEI spark tester helps in the diagnosis of the ignition system by stress testing the ignition coil and any other component between it and the spark plug (like: a distributor cap, distributor rotor, ignition cables, etc).
As you can see in the photo, the tester looks like a spark plug with some very big and obvious differences. The biggest one is that there's no Ground electrode hovering over the center electrode. Instead, there's a huge air gap between its center electrode and its body.
When you connect the spark tester to the spark plug cable or the ignition coil boot (for Coil-On-Plug Systems) and crank the engine, the HEI spark tester (OTC 6589 Electronic Ignition Spark Tester) forces the ignition coil to produce its maximum output so the spark can jump across the very large air gap. This action stress-tests the ignition coil.
The voltage necessary to fire the HEI spark tester is around 35,000 Volts. This kind of voltage produces a very bright and bluish spark that's also audible. This method of testing for spark is the best one and does not cause any damage to the components.
If the ignition coil or whatever component that is in between it and the tester are on their last leg, you'll get a NO-SPARK result on the tester.
The beauty of this tool lies in the fact that you get one of only two results to interpret. Either a spark jumping from the center electrode to the outside metal body or no-spark. That's it! It's a very easy tool to use.
So, lets say that you're testing the ignition coil and you got a no-spark result. This would indicate that the ignition coil is faulty. To be absolutely certain, you would only need to check the power and control circuits of the coil. If the coil is getting power and it's being pulsed by its control module, the ignition coil is bad!
You can buy it here: OTC 6589 Electronic Ignition Spark Tester.
Behind every great tool, there's a great test. To effectively use this tool, I recommend reading the following articles (within this site) to learn more about this tool:
- How To Test The Igniter, Ignition Coil Accord, Civic, CRV, and Odyssey. This article is the most comprehensive article on how to use the HEI spark tester to test the ignition coil, the distributor cap, the distributor rotor, and the spark plug wires. I highly recommend this article!
- How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L). Another good article that I highly recommend on how to use the HEI spark tester, this time to test a modern coil pack type Direct Ignition System (DIS).
- Carbon Tracks Are A Common Cause Of Ignition Misfires.
- No Start Testing And Diagnostic Basics. Article on the basics of testing a CRANKS BUT DOES NOT START CONDITION.
- Automotive Diagnostic Tips And Techniques: The Ignition Coil Easy to understand explanation of how the ignition coil and the ignition system works.
IMPORTANT you'll notice in most of the photos, in this site, the HEI tester is Grounded by a battery jump-start cable. Why? you might ask.
Well, more and more, plastic is replacing metal in the engine compartment and so it's difficult to find a good Grounding point. And if you do find one, the spark plug cable or the ignition coil boot is not long enough to reach it with the tool attached.
Also, the only (and it's a big one) fault with this tool, is that its Grounding clip is very flimsy. If you use it, it'll break in a few uses. So I find it easier to Ground the tester with the jump-start cable.