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Don’t worry, it’s not just you. Everyone dropped their first, or likely fortieth, F-bomb when their dad had them hold the spark plug while he hit the kick starter on their dirt bike. While it might have seemed cruel and unusual, followed by his raucous laughter and a lifetime of vengeful plotting to get him back, the power of that shock is something you kept in mind every other time you worked on a vehicle’s electrical system.

Luckily, that’s the kind of lesson you only need to learn once and, thankfully, it’s not the only way to test a spark plug. Like all other things mechanical, spark plugs will see their day. But just because a plug isn’t firing doesn’t mean it’s the problem. Lack of spark can be on account of plenty of other faulty electrical components.

That said, it pays to know how to test a spark plug so you can pinpoint the issue. There’s more than one way to skin a cat, though. So, it’s a good thing you’ve got The Drive’s brainiac team to teach you the ways that won’t leave your hair standing up straight.

A spark plug is a simple device that turns the ignition system's energy into spark, which ignites the fuel mixture. The short version of how they work is by sending electricity through the plug, so an arc breaches the gap between the center electrode and the ground electrode. 

There's more to it than that, but that's all we need to know to understand the tests we're performing as we’re just trying to ensure the plug can perform that very task.

Why are we performing a spark plug test? Spark plugs are cheap. So, it's not a big deal to replace them if they go bad.

There are plenty of contributors to a misfire. It can be a lack of fuel, compression, or spark. And if it's a lack of spark, it can be due to a bad plug, coil, ignition module, distributor, or spark plug wire. So, if you fall into the habit of throwing parts at a car until it works again, you can wind up deeper in the hole than you could ever imagine.

As a rule of thumb, you always want to start with the simplest and easiest solution and gradually work your way up the latter when troubleshooting. In the case of a misfire, the easiest place to start is by checking the spark plugs.

Sometimes a visual inspection is enough to determine if a plug is faulty. Over time the center electrode will wear away, and it can't perform its job. But what if it's not? How can you tell for sure if the spark plug isn't firing?

We're going to talk about two tests you can perform to test out spark plugs. Both are relatively easy and require little more than basic hand tools. By performing these tests, you can quickly determine whether or not the spark plug is the source of your problems.

Because we are highlighting two different ways to test plugs, there are variable safety considerations. One of which only requires a multimeter, but the other involves working with an exposed plug under the hood. For that second method, you want to keep these safety tips in mind. 

The good news is that you’re only going to need a few tools to perform both of these tests. There are more professional ways of doing it, but since we’re talking about a home job, we’re going to keep it on the cheap. That said, you probably have some of these tools on the ready, but we’ve gone ahead and hyperlinked each in case you don’t!

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won't need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of the clink.

As much as The Drive loves to put the "you" in do-it-yourself, we know that not everyone has the proper tools, a safe workspace, the spare time, or the confidence to tackle major automotive repairs. Sometimes, you just need quality repair work performed by professionals you can trust like our partners, the certified mechanics at Goodyear Tire & Service.

Here are a few of The Drive’s pro tips.

You’ve got questions, The Drive has answers!

A: How much resistance a plug should have ultimately depends on the manufacturer’s specifications. While most spark plugs for passenger vehicles should have somewhere in the 4,000-8,000 ohms neighborhood, your exact plug may call for different values.

A: Usually, visual inspection is enough to determine if a plug wire is bad. Any signs of wear or rot are telltale signs that it’s time to replace them. You can use a multimeter to test the resistance to be sure.

A: The grounding test is performed to determine if a plug is firing. You want to watch the center electrode to see if a strong, blue spark is created. Alternatively, you can use a spark plug light. However, this only shows if a signal is being sent to generate a spark and not that the plug is, in fact, firing.

A: If you have a misfire, your engine will lack in power and economy and run rough. But that’s the least of your issues. Unburnt fuel washes the walls of any lubricant and eventually pollutes your oil. So, it’s worth fixing the misfire ASAP.

A: The energy sent to spark plugs has high voltage but low amps. Amps are what’ll kill you. So, even if the shock hurts, it probably won’t kill you unless you have a serious heart condition.

Learn more about spark plugs with this video.

Fluke 117/323 Multimeter and Clamp Kit

Gearwrench 5-Piece Magnetic Swivel Spark Plug Socket Set

ARES 70053 - Spark Plug Pliers

Williams 50666 3/8-Inch Drive Socket and Drive Tool Set

We’re here to be expert guides in everything How To related. Use us, compliment us, yell at us. Comment below, and let’s talk! You can also shout at us on Twitter or Instagram, here are our profiles. Got a question? Got a pro tip? Send us a note: guidesandgear@thedrive.com.

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