How to Test a Spark Plug with a Multimeter (Complete Guide)

Spark plugs are vital in all gas engines, igniting the air-fuel mix with precision timing.

Spark plugs can wear out, leading to higher fuel consumption and reduced power. It’s smart to test them regularly. Here’s how.

Quick Summary:

🚫 Step 1: Fuel Supply Off
πŸ”§ Step 2: Remove Wire/Coil Pack
πŸ› οΈ Step 3: Spark Plug Removal
πŸ” Step 4: Multimeter Time
πŸ“ˆ Step 5: Probe Check
πŸ§ͺ Step 6: Testing the Plugs
πŸ“Š Step 7: Reading the Results

This article is packed with a 7-step process for spark plug testing, ensuring you get the most accurate results. Plus, I’ll share some of my own experiences and tips for troubleshooting scenarios you might encounter.

Items Required for Testing the Spark Plugs

Alright, DIYers, here’s the lowdown on the must-have tools for spark plug testing.


  • Multimeter: This is your go-to for resistance checks. I’ve got an old, reliable one that’s seen more engines than I can count.
  • Spark Plug Socket: Essential for smoothly removing and installing spark plugs. I have had a set with me since my first project car.
  • Spark Plug Wire Puller (for Older Rides): If you’re working on a classic, this tool is a lifesaver.


  • Spark Plugs: The stars of the show. Always have a few on hand.
  • Sockets for Coil Pack Cars: Modern cars need these. They make dealing with coil packs a breeze.

Testing Spark Plugs: A 7-Step Guide

Step 1: Fuel Supply Off

For fuel-injected cars, pull that fuel pump fuse. On carbureted beauties, disconnect the pump. I had to dry-run an old muscle car before testing – it’s a crucial step.

Step 2: Disconnect Plug Wire/Coil Pack

A man with blue gloves is working on the engine of a car
Video | Scotty Kilmer

Next, remove the coil or spark plug wire. Spark plug pliers can be a hand-saver here. I learned this is dealing with a vintage Chevy.

Step 3: Remove the Plug

A person with blue gloves holding a car's spark plug
Video | Scotty Kilmer

Time to remove the spark plug. It’s central to your test. I had a tough one on a classic roadster – patience is your friend here.

Step 4: Multimeter to Ohms

Set your multimeter to ohms for resistance checking.

Step 5: Probe Test

Ensure no resistance between the multimeter probes. Skipping this can lead to misleading results.

Step 6: Testing Different Plugs

Touch one multimeter leading to the terminal end of the plug and the other to the center electrode.

  • Copper Plugs: Connect the multimeter and check for a standard range. These can show wear quickly but are common in older models.
  • Iridium and Platinum: These need more finesse due to their finer properties. Expect a consistent range, but be aware they may require more sensitive multimeter settings.
  • High-Performance Plugs: Used in sports cars, they might show varied readings. Keep an eye out for any abnormal fluctuations.

Step 7: Analyze Readings

Look for readings within the 4,000-8,000 ohms range, but they can vary. Different plug types can show different ranges – I experienced this with various models over the years.

Testing spark plugs isn’t just about the steps; it’s about understanding the heart of your engine. Each type of spark plug can tell a different story.

Safety First: Spark Plug Testing Tips for Beginners

Here’s how you keep it safe:

  • Gear Up with Safety Gloves: Always protect your eyes and hands. I’ve had my share of close calls – a rogue spark or a hot engine can surprise you.
  • Cool Down the Engine: Patience is a virtue here. Don’t rush to pull those plugs if your engine’s hot. Trust me, a burn can put a serious damper on your day.
  • Watch for Moving Parts: Ensure the engine isn’t cranking or running. I once got my sleeve caught in a belt – not fun.
  • Respect the Spark Plug’s Power: With the ignition engaged, steer clear of the spark plug. Those volts can pack a wallop. I’ve felt a jolt or two in my time; you want to avoid it.

Stay safe and enjoy your DIY journey – it’s all part of the fun and learning!

Comparative Analysis: Healthy vs. Faulty Spark Plug Readings

A man holding two spark plug of a car

Let’s break down the differences between a healthy and a faulty spark plug through a comparative analysis. I’ve come across both in my DIY adventures and here’s what I’ve learned:

Healthy Spark Plug: A well-functioning spark plug typically shows resistance readings within the manufacturer’s specified range, commonly between 4,000 and 8,000 ohms. I recall checking a nearly new plug on my buddy’s sedan – it showed a perfect 6,000 ohms, right in the sweet spot.

Faulty Spark Plug: Faulty ones, however, tell a different story. They often show erratic or inconsistent readings. I once tested a plug on an older pickup, and the multimeter went haywire, jumping everywhere. You might also get no reading or resistance values way out of the normal range, indicating a worn-out or shorted plug.

Troubleshooting Spark Plug Issues: Practical Scenarios and Solutions

Let’s dive into some real-deal troubleshooting scenarios you might face while testing spark plugs with a multimeter. I’ve been in a few tight spots myself, and here’s what I’ve learned:

Inconsistent ReadingsFluctuating meter readings.Tightened connections and checked meter accuracy. With iridium plugs, ensure the meter is sensitive enough as it can have finer resistance characteristics.
No ReadingNo resistance was shown.I checked the probe contact. With platinum plugs, ensure they’re not coated with deposits, which can insulate and cause no readings.
High ResistanceResistance is too high.It indicates wear, especially in copper plugs known for shorter lifespans. Replacing them rejuvenated an old roadster I worked on.
Low ResistanceBelow are the expected resistance values.It could mean a short. In high-performance plugs, this can indicate internal damage, necessitating replacement.

Each plug type – iridium, platinum, or copper – has nuances. For instance, iridium and platinum plugs often last longer but may require more sensitive equipment to diagnose.

Copper plugs, while more traditional, might show wear more quickly. Remember, knowing your plug type is key to effective troubleshooting!

Frequently Asked Questions

  • Can I Test Spark Plugs Without Removing Them?
    • It’s best to remove them for accurate testing. Testing in place can give you a rough idea, but for precision, take them out. I learned this while working on an old muscle car – a thorough job makes all the difference.
  • What Causes High Resistance in Spark Plugs?
    • High resistance can be due to wear and tear or build-up on the plug. I’ve seen old plugs with so much build-up they were practically fossils!
  • Does a No Reading Always Mean the Spark Plug Is Bad?
    • Not necessarily. First, ensure proper contact with the terminals. If there’s still no reading, then it’s likely the plug is bad. I had a plug once that seemed dead, but it was just a bit of corrosion messing with the contact.
  • Can Spark Plugs Affect Fuel Efficiency?
    • Absolutely. Faulty spark plugs can lead to inefficient combustion, thus affecting fuel efficiency. I had a truck once that guzzled gas due to bad plugs – a quick fix made a huge difference.




Website Resources:

Video Resources:

Electro University

Scotty Kilmer

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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