How to Test a Spark Plug (With and Without Spark Plug Tester)

The spark plug is an essential part of your vehicle’s engine. It is critical to test the spark plug regularly to ensure that it is constantly functioning properly. So, how do you check a spark plug?

Connect a spark plug tester to the ignition wire if you have one. Then, connect the tester’s other end to the spark plug. Start the engine and check the spark plug tester for a glow.

Understanding how to test a spark plug is a critical component of diagnosing any small engine. Continue reading to discover how to use a spark plug tester.

Spark Plugs

Your engine is an amazing piece of machinery intended to convert the fuel into a real movement. But how does it accomplish this? 

The answer is the internal combustion principle. To convert your car’s gasoline from a source of potential energy to a source of kinetic energy, your engine must find a method to release it, which it accomplishes through the combustion process.

This procedure is made possible by the engine cycle. Your valves fill your cylinder with a highly explosive mixture of air and gasoline during the engine cycle.

As your engine’s piston travels higher, it compresses this mixture until it’s in an exceedingly compact space, generating even more potential energy.

At the height of pressure, your engine ignites this mixture with a little spark, causing an explosion that pulls the piston back downward, rotating the crankshaft in your engine and producing the power that propels your vehicle forward.

Your spark plugs are responsible for supplying the spark that burns the air/fuel combination, resulting in the explosion that causes your engine to create power.

These small but basic plugs generate an arc of electricity between two not touching leads but are near enough that electricity may jump the distance between them.

In general, your spark plugs are constructed of incredibly robust material and can sustain millions of explosions before wearing out or needing to be changed.

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However, it is true that over time, explosions and corrosion cause smaller or weaker sparks, resulting in diminished engine performance and other concerns such as misfiring or failure to fire.

Types of Spark Plugs

Hot Spark Plug

Hot spark plugs, used in many passenger automobiles, contain greater insulation to transmit heat slowly, maintaining high temperatures to blow off carbon deposits and avoid early fouling. This allows for longer intervals between spark plug replacements.

  • Longer insulation nose
  • Heat is transferred slowly
  • Tip stays hotter for longer
  • Removes carbon deposits by combustion

Cold Spark Plug

Cold spark plugs are ideal for high RPM engines and other applications where the engine runs at high temperatures. Because they transfer heat more quickly, cold spark plugs can get filthy and clogged faster because they do not get hot enough to consume carbon deposits.

  • Shorter insulator nose
  • Heat is transferred more quickly
  • The tip stays colder for longer

Spark Plug Test

A spark plug is a basic mechanism that converts the energy from the ignition system into a spark, which ignites the gasoline mixture.

The simple description of how it functions is that electricity is sent through the plug, causing an arc to form between the central and ground electrodes.

There’s so much more to it, but that’s all you’ll have to know to fully comprehend the tests since we’re simply trying to guarantee the plug can do that.

Why Is It Important To Test The Spark Plugs?

Why are we testing the spark plugs? Spark plugs are inexpensive. As a result, replacing them isn’t a huge concern if they go faulty.

If there is no spark, it might be a faulty plug, coil, combustion module, distributor, or spark plug wire. So, if you get into the habit of tossing parts at a car until it starts working again, you may end up deeper in debt than you ever imagined.

When troubleshooting, always start with the most basic and best answer and progressively work your way up to the latter. In a misfire, the simplest place to begin is by inspecting the spark plugs.

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A visual check may be sufficient to identify if a plug is defective. The central electrode will wear away over time, rendering it incapable of performing its function. What if it isn’t? How can you be certain that the spark plug is misfiring?

We’ll go through how to use a Spark Plug Tester to check the condition of your spark plugs. You can quickly identify whether or not the ignition is the source of your difficulties by conducting some tests.

Spark Plug Test Tools

1. Professional Tool: Inline Spark Plug Tester

As the name implies, it checks the spark plug, or more precisely, if there is an electrical charge capable of creating a spark. This gadget is extremely simple to use and safe.

A spark plug tester is a useful tool for determining whether or not your spark plug is operating properly. This tool can also save you a lot of time by helping you to determine if the problem is with your ignition or not.

You may use a Spark Plug Tester to check whether or not an electrical current is reaching your engine’s spark plug. This current is utilized to ignite the air-fuel combination inside the engine’s cylinder, resulting in power.

While it cannot always tell you exactly what’s wrong with your car, it can tell you if each spark plug is receiving an electrical charge from the ignition coil. If it isn’t, there’s something wrong with the spark plug wires or the coil itself.

2. Simple and Highly Effective Method: How to Test a Spark Plug with Multimeter In One Minute

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How To Use a Spark Plug Tester

Using a Spark Plug Tester requires some materials to fully utilize it for checking if your spark plugs are working fine or not. Continue reading below to learn more about using a spark plug tester.

Supplies Needed

Before using a Spark Plug Tester, you’ll need some materials. Check below for what you’ll need.

  • Spark Plug Wire Puller (For older vehicles without coil packs)
  • Multimeter (for resistance test)
  • Spark Plug Socket
  • Sockets (for cars with coil packs)

Utilizing an Inline Spark Plug Tester

Spark plug misfire occurs when the sparks that jump the space between the electrodes are irregular in their timing.

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This can cause your engine to stutter, lose power, and possibly produce black smoke (due to unburned fuel not being ignited in the combustion chamber). The actions below can be followed to determine if you are suffering spark plug misfire.

Unplug the spark plug lead from the spark plug first. Plug your spark plug tester into the spark plug lead after that.

Then connect the spark plug tester to the spark plug, forming a connection from the lead to the spark plug. Start the engine and check the gap in the spark plug tester to determine whether the timing is off.

If you’re having trouble, you can try changing the spacing between the electrodes and attempting again. However, if it still doesn’t work, it would be best to use a spark tester to check the ignition or replace your spark plug.

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Things to Remember When Testing Spark Plugs

It’s best not to forget anything before testing your spark plugs. Make sure to remember these things to ensure you do everything safely and properly.

Safety Wear

Before you do anything else, you should always wear safety gear when tinkering with your car. A pair of rubberized gloves and goggles will do.

Let the Engine Cool Down

When the engine is hot, do not attempt to pull the plugs. There are a lot of pieces under the hood just ready to grill you. This includes plugs that aren’t in perfect condition. So, before you go in, make sure to let the engine cool down.

Moving Parts

The engine isn’t running for the grounding test, but it’s still cranking. Keep that in mind and stay away from any moving parts.

Turn Off Ignition

Before touching anything, you must turn your ignition off first. When the ignition is turned on, do not touch the spark plug. Take my word for it: it’s going to feel awful.

Frequently Asked Questions (FAQs):

Can a Spark Plug Shock Kill you?

The low amperage is unlikely to kill you, which is a good thing. However, on average, 20,000 volts pass via the spark plug. So, even if it does cause a high shock to you, it is unlikely to kill you.

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How to measure spark plug voltage?

A spark plug generates high voltages ranging from 25 to 45,000 volts. Measuring the voltage isn’t essential because a visual inspection would determine whether or not it’s sparking vigorously – either using the grounding method or a spark plug tester.

Can you make your spark plug tester?

Yes, you can actually make your own spark plug tester at home. Here’s how you do it:

To begin, remove all of the spark plugs from the cylinder blockheads. Then you must examine them carefully to see whether there is a soot buildup. If there is a soot deposit, remove it with a piece of tiny size emery paper.

The second item to consider is the backlash between these two electrodes, which should be between 0.7 and 0.9 mm. If it’s less, you’ll need to bend the side electrode a little, and if it’s more, you’ll need to bend it inside somewhat.

In addition, you must inspect the spark plug to see if it creates a spark. You can test it by connecting four plugs with wire, isolating it, connecting the high voltage wires, rotating the engine with the starter, and observing the spark.

The issue is that it requires two individuals to complete it. Generally, the engine should be spun with the starter to see whether there is a spark from the plug.

For testing, you’ll need a tiny crocodile clip with wire, a larger crocodile clip, a piezoelectric element from a lighter, and a spark plug.

Suppose you have no tools, but you’ve got the lighter with the piezoelectric element, don’t worry. You may also check the spark plug in this way.

First, you must carefully solder everything before isolating it. It is critical to avoid spark leaks. If you’re in a pinch and don’t have any tools but have a lighter with a piezoelectric element, you may check the spark plug this way.

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How do you check for a spark?

Detach the spark plug’s wires to test the ignition. Hold the spark plug wire end against a metal surface. If the spark plug is in good condition, you will see a spark or hear a crackling noise. This indicates that electricity is sent to the spark plug through the wire.

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What is the first step in testing spark plugs?

Before you start testing your spark plugs, make sure you check the basics first:

  • Check to see if you have enough gasoline
  • Examine your battery
  • Scan your fuse box


You can use a spark plug tester by simply unplugging the HT lead and attaching the device to the end of the HT lead and the spark plug base. Start the engine as usual, and the tester will light up if it detects a significant electrical input.

If no light is observed, more diagnostic work is required. Swap the plug first, then the HT lead. If you still have no luck, work your way down the ignition system until you identify the problem.

It is an essential aspect of diagnosing any engine. Also, it will just take you a few minutes and may cost you very little or nothing at all. A spark plug wrench and a spark plug tester are required tools. However, the latter is optional.

When your vehicle’s engine begins to exhibit symptoms, don’t hesitate to test the spark plug. If you are unsure if you can complete the exam independently, you may always seek expert assistance. Allow a mechanic to inspect it for you.

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