See full version: The HEI Spark Tester (The Best Spark Tester On the Market)
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! [links]
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 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. Thats it! It's a very easy tool to use. here
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. more
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:
Step 2: Drill a small hole in the thickest part of the metal (where the wrench goes on). Use a metal screw to attach a length of wire, a couple of feet, to the body of the spark plug. To the other end of the wire, solder or otherwise attach a big alligator clip. (Witness my amazing drawing skills - you should get the idea)
When diagnosing engine stumbling or misfiring, its often useful to gauge the intensity of the spark at each cylinder. This way, you can at least make sure the HT (high tension/high voltage) side of ignition system is in good working order, that is, the coil, rotor, cap and spark plug leads. The usual vendors offer a variable gap spark tester for about $5-10 but you can make one yourself just as easily out of an old spark plug for nothing. Here's how:
Since the tip is cut off, the spark will have to be stronger to jump the wider gap. It is harder for a spark to form in a compressed cylinder so it more accurately represents the spark performance under running conditions. You may want to disconnect all of the spark plug wires before beginning the test, to prevent the vehicle from actually starting when you engage the starter motor. To use the tester: [links]
Step 1: Take an old spark plug and cut off the L-shaped tip,
and clean up the center electrode and surrounding metal with a bit of sandpaper. [links]
The spark won't jump as far as compression is increased.
Set the plug gap to what the manual says and forget it.
The proper tool for plug gap is the service manual. [links]
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CASE 4: Got NO SPARK from two different spark plug boots that are not 1 and 4 or 2 and 3. Go to: TEST 4: No Spark From Two Boots that are NOT Paired Cylinders.
No need to pay attention to whether the other spark plugs spark or not that are attached to the other boots. more
IMPORTANT: In the photo above you'll notice that all of the boots are labeled with a number. This number is the cylinder number to which this boot belongs to. I've included this info because you'll need to know the number of the cylinder to interpret your test results correctly.
CASE 5: Got spark on ALL spark plug boots. This is the correct and expected test result.
To be a bit more specific, we're gonna' make sure that each ignition coil cover boot is firing off Spark. This will require a very unusual test (see photo above). I can tell you from personal experience that doing it this way will help you find ignition system problem causing the misfire without having to guess at it.