How to Test an Ignition Coil with a Multimeter (4-Way Guide)

Do you suspect that you are dealing with a faulty ignition coil? Don’t worry below; ill teach you how to test an ignition coil.

Testing the Ignition Coil

I’ll share a four-step guide for testing your car’s ignition coil. Once you’ve established an existing problem, you can proceed to consult your mechanic.

1. General Inspection

As the name suggests, this method entails a general inspection of your ignition coil. Check your spark plug wires for the presence of burns, melting, burns, or leakage if your canister coils are old. These are signs that something is wrong, and a careful check should be done as soon as possible.

2. Spark Test

The most sensible place to begin is with your car in park, and the engine switched off. Locate the ignition coil of your car under the hood. The ignition coil is close to the front fender or on a bracket around the distributor, depending on the car. Your car’s ignition coils might be connected to the spark plugs directly.

If you’ve been driving the car, allow it to cool for about 60 minutes to avoid fatal injuries – even if you’ve been running it for as little as 20 minutes. The engine can potentially heat to 200 degrees.

Using gloves and insulated tools, remove one spark plug wire from its plug. These wires normally run individually from the distributor cap to each car’s spark plugs. Using a spark plug socket, pull out the spark plug. Be careful that nothing drops inside the exposed hole. The best thing to do is to cover it with a rag because if anything enters the hole, it could damage the engine.

With the spark plug still outside, reconnect it to your car’s spark plugs wire. Use protective equipment to prevent electric shock. The exposed spark plug has a threaded part. Have it touch any piece of engine metal.

Next, take out the fuel pump relay to prevent the engine from starting. Don’t worry if the plug generates a plug. Request someone to crank the engine and see if there is a blue spark. Its presence says that the ignition coil is functioning well. However, if you see an orange spark, it says that the plugs aren’t receiving enough power from the ignition coil. The absence of sparks means the absence of power. Now, you can return the detached spark plug.

Using a spark plug tester is a safer way to check if your spark plug wires are faulty. It will help you prevent spark plug damage, besides saving time. Don’t attach the spark plug tester to the wire if you can access the spark plug. Instead, let the spark plug tester and wire touch. After grounding the alligator clip, ask your friend or someone close by to crank the engine. Watch out for sparks in the gap of the tester. Another advantage of using a spark plug tester is that your combustion chamber will not be exposed to debris and other risky objects.

3. Testing Ignition Using A Multimeter

It is important to know how to test an ignition coil with a multimeter – a digital multimeter. Check your manual to ascertain your coil’s correct resistance reading. Now, lift your hood and get hold of the coil. Disconnect the wiring harness of the ignition coil.

analog multimeter

Note that ignition systems have primary and secondary circuits, requiring checking. Connect your digital multimeter to the positive and negative terminals to obtain the primary circuit reading. A 0ohms reading on the multimeter display indicates a short ignition coil needing a replacement. If the reading exceeds the range specified in your car’s manual, your ignition coil is incomplete and needs replacing. If you’re using an analog multimeter, check the guide here on how to read them.

Multimeter reading of a functional spark plug

Connect your digital multimeter’s positive pin to the positive terminal to obtain the secondary circuit reading.

Next, attach your multimeter to the high output terminal connecting to the sparkplug. Your car’s manual should tell you a figure to expect in the multimeter display. However, a reasonable range is between 6000 and 10,000ohms.

A reading not within the prescribed range means trouble with the ignition coil. If you find any faulty coil or coils, have them replaced and then go for a test drive to ensure their effectiveness.

testing a faulty spark plug

4. Swapping Coils

Swapping coils is the simplest and the fastest way of testing ignition coils. As the name suggests, the process entails swapping a car’s ignition coil with the ignition coil of another car that’s already been inspected. This procedure works amazingly well on any car with coil-on-plug, multi-packs, or single coils.

In such instances, you will be dealing with a misfire on a given cylinder. If, for instance, you have cylinder 3 misfires on a car with coil-on-plugs, remove another coil, say from cylinder 6 and swap it with cylinder 3 coil. Clear your engine codes if you can access a code reader. (2)

Next, start the car’s engine and let it run for a few minutes. If you are dealing with a faulty ignition coil, expect to see an engine code for ‘Misfire – Cylinder 6’ since the faulty coil from cylinder three was swapped to cylinder 6. Next, remove the cylinder 6’s coil you moved and replace it.

If, upon swapping the coils, you still record a misfire on cylinder 3, and it stays intact, the coil is not the culprit. Maybe you are staring at an ignition module problem, spark plug issue, faulty connector or lead, a defective fuel injector, or the cylinder is experiencing mechanical internal engine issues.

Signs of Damage

What are the signs of a damaged ignition coil?

They include:

  1. Is your car backfiring? Backfiring cannot go unnoticed. If you are dealing with backfiring, you should hear a loud sound accompanied by a shaking noise. Is your car lurching forward, producing black smoke, or smelling of gasoline-like there is leakage? Can you smell gasoline leakage? It’s hard to ignore all these tell-tale signs. (1)

    While these problems can be linked to low fuel pressure, it is largely due to a fault in ignition coils. An issue with the ignition coil can interfere with the spark plug’s ignition timing, causing misfiring.
  2. Have you noticed that your engine keeps stopping and starting for no reason you can explain? This issue is dangerous because it compromises your safety and other road users. If the ignition coils under the hood begin to fall, your car could stall.

    The spark plugs will receive uneven electrical charges because the coils produce irregular sparks. While the car can still run with malfunctioning coils, starting is not easy. That’s why it is important to learn how to test ignition coils.
  3. Is your car consuming more fuel than it usually does? Your ignition coils could be the culprit. The inability of the ignition coil to transmit enough energy to the spark plugs forces the car to burn and consume extra fuel. There isn’t any other way for your car to keep running.

    You can only tell if your car uses more fuel than usual if you know how many miles per gallon it generally drives. If you don’t have this information, check the odometer on the dashboard.
  4. Does your car suffer occasional idling when you least expect it? You might want to check your coil pack or the ignition coils if your car shows less power while on the run – a clear sign that something is wrong with the ignition system. Here’s a more detailed guide on checking and testing your engine’s coil pack.

Wrapping Up

Diagnosing ignition systems or coils can, at times, be difficult and time-consuming. Swapping parts can sometimes prove expensive and ineffective. Testing ignition systems using a multimeter appears more straightforward than the other three techniques. Suitability will defer from one person to another depending on the resources available.  






References
(1) gasoline leakage – https://www.medicalnewstoday.com/articles/321277
(2) engine codes – https://www.familyhandyman.com/project/vehicle-diagostics-how-to-find-engine-code/

About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.