How To Check Spark Plugs Without Removing Them?

Are you experiencing a tough time starting your car or struggling with a sluggish engine? These and many more malfunctions are the characteristics of bad spark plugs that need a replacement like “yesterday.”

However, identifying the exact spark plug with the problem can be a little bit tricky. Of course, performing table testing can be time-consuming as well. So, the way out is to figure out how to check spark plugs without removing them.

The process of testing for a bad spark plug, among all the others, is pretty straightforward if you know what to do. So, without much ado, let’s delve into the possible answers to the key question in this article.

How To Check Spark Plugs Without Removing Them

Spark plugs look insignificant in size; however, they can cause your car to break down and get you stranded when you least expect. That’s why you need to keep the components in good condition at all times.

Meanwhile, if you suspect that you may have a worn-out spark plug(s), these recommendations can help you identify the exact ones without taking any of the plugs out of your car’s engine compartment.

how to check if spark plugs are firing

Read Also: Iridium Vs. Platinum Spark Plug: What are The Differences?

Option 1: Disconnect each spark plug wire with the engine running

Firstly, start your car and allow the engine to run while you disconnect the spark plug wires one after the other. Whereas if your car is running already, just go ahead to remove the wires one after the other.

The check is very simple! If you remove a particular spark plug wire and the speed of the car’s engine drops or it starts running a little bit rough, that’s a sign of a good spark plug.

On the other hand, if you disconnect a spark plug wire and no significant changes occur in the engine’s operation, that’s it right there – the faulty spark plug. Ensure to perform this exercise across all the spark plugs. Also, make sure you replace the bad ones with spark plugs.

If you’re contemplating how to test a spark plug without a multimeter, implementing the strategy above is one of the ways you can spot a bad spark plug without the device.

Option 2: Conduct a spark plug ignition test

In order to conduct a spark plug ignition test, carefully disconnect the spark plug wire, insert a screwdriver in it and hold the end close to any metal surface. A good spark plug will trigger a crackling sound or give off a spark.

The signals reveal that the voltage is linking through the wire down to the tested spark plug. Therefore, ensure to do this with all the spark plugs and their respective wires to ascertain the bad ones, among others.

Option 3: Perform a spark test with a spark plug tester

Lastly, using a spark plug tester can help you ascertain whether you have a bad spark plug or not. So, get a good spark plug tester from an auto parts shop across the street. Meanwhile, ensure to turn off your engine, remove the key and disconnect the battery’s negative terminal before commencing the test.

After that, locate the spark plugs in the cylinder and pull out the boot on the first plug. Then, press the spark tester’s boot on the spark plug and let it click. Thereafter, connect the original spark plug boot onto the spark tester and fix the spark plug wire to the spark tester’s other end.

Now, you can reconnect the battery’s negative terminal and start the car. Meanwhile, ensure that a friend starts the car while you look at the spark plug tester. If the light flashes rapidly, the spark plug is okay. If it doesn’t flash at all, the spark plug will require a new replacement.

Also, note that a spark plug tester can be helpful for those asking how to check if spark plugs are firing properly. The device is built holistically to enhance your DIY operations.

how to test a spark plug with multimeter

Read Also: Oil in the Spark Plug Well: Symptoms, Causes, and Fixes

FAQs

Q: Can I test spark plug with multimeter?

Sure! A multimeter can be useful in testing a car’s spark plugs. Like an Ohm meter, a multimeter is also designed to test electrical resistance and perform other functions.

It is quite straightforward to test your car’s spark plugs to determine whether any of the plugs have resistance or a short. If you’re contemplating how to test a spark plug with a multimeter, the following steps will guide you in using the device perfectly:

  1. Connect the test leads (black and red probes) to the multimeter
  2. Set the multimeter to “Ohms.”
  3. Touch the black and red probes together (The multimeter would read zero Ohms).
  4. Separate the two probes (The meter would read infinite).
  5. Take the ignition wire off and unscrew the spark plug to be tested.
  6. Set the resistance to about 20K Ohms (although the spark plug should read around 4,000 – 8,000 Ohms in most cases).
  7. Place the black probe from the multimeter on the spark plug’s terminal. Then, place the red probe on the center electrode at the tip (make sure you don’t allow it to touch the ground electrode). Carefully press the probes to make them connect properly.
  8. Check the reading on the meter. The resistance should be between 4,000 – 8,000 Ohms. Kindly check out this video for a classic example.

Q: How do you make a spark plug tester?

Usually, you can get a nice spark plug tester in an automobile parts or accessories shop across the street. However, it is possible to build a homemade spark plug tester with some common materials around you.

Some of the materials you need include a regular spark plug wire, a transparent tube, and a piece of a short screw with round edges on one end. Once you have these materials, simply cut the spark plug wire into two halves.

Then, cut a little piece of the tube and fix it at both ends of the two-half spark plug wire you’ve just cut. So, the tube becomes the connecting link between them. Make sure you leave a tiny space of about half an inch between the two half spark plug wires.

After that, fix the screw into one of the tips of the spark plug wire. Now, you can connect the side of the tester with the screw on it to your car’s spark plug wire boot and the other end onto the spark plug. Then, ask a friend to start the car while you observe the tiny tube in between the two half spark plug wire for a rapid flashlight.

Q: How many ohms should a spark plug read?

Based on the Society of Automotive Engineers’ recommendation, a spark plug is expected to read around a maximum resistance level of 12,000 Ohms per foot. Nevertheless, some Original Equipment Manufacturers (OEMs) have their unique spark plug resistance levels.

In that case, you will likely need to look up your plugs’ manufacturer’s manual to find the recommended resistance level. However, whatever the case may be, ensure to replace old spark plugs once they start expressing symptoms of a bad spark plug.

Q: What does a weak spark look like?

A weak spark looks like red or orange colors. It may be difficult to see it in daylight. A good spark displays blue–white. This spark is obvious anytime, even during daylight. So, identifying a good or weak spark is not rocket science.

If you’re having a tough time starting your car, ensure to find out how to check for sparks by yourself in order to perform the test to help you ascertain whether the problem is from the spark plugs or not.

However, if the plugs seem okay, you may have to look at the fuel system or other components that work in synergy with your car’s ignition process.

Q: How do you check for bad spark plugs?

There are various ways to check for bad spark plugs in a car. Sometimes, you may have to remove the components, while at other times, physically inspecting the spark plugs in the engine compartment can reveal the true conditions.

For instance, if you compare your old spark plugs with new ones and discover excessive wear on the electrode (tip), you most likely have bad spark plugs that need a replacement ASAP. Also, if you find fuel or oil contamination on the plugs, kindly replace them.

Lastly, you can use a digital multimeter to test whether your car’s spark plugs are bad or intact. The Ohm meter setting can help you verify the conditions of your spark plugs. Using the multimeter will be helpful if you’re asking how to check if spark plugs are bad.

Final Words

The alternative approaches above in this article are clear-cut guides to help you understand how to check spark plugs without removing them and perform in need. In addition, the recommended strategies have simplified the process of diagnosing a faulty spark plug in need of a new replacement.

So, you don’t have to struggle with a lousy spark or face difficulty starting your engine anymore. Therefore, if you’re experiencing any symptoms of a faulty spark plug, take a moment to perform a spark test with a spark plug tester or try out any of the other recommendations above.

Learn More:

Osuagwu Solomon

Osuagwu Solomon is a seasoned automotive technician for the past 9 years, and a technical writer. He loves writing about auto professional repair guides, DIY repair guides, and buyer’s guide. After spending six years in the automotive workshop, he decided to impact his knowledge to people aside his domain, and he has achieved this by centering his Automotive writing skills on REPAIRS.

Recent Posts