The Garage Maintenance & Repair

How to Troubleshoot Your Car’s Ignition System

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What’s the fastest way to a mental breakdown in your garage, and why is it an ignition issue? No doubt, that stress headache comes on strong when your car was running a minute ago, whereas now it’s shaking like a leaf on a tree or won’t run at all. Something is definitely wrong with your ignition system. You’re going to have to figure it out ASAP.

Unfortunately, that can be easier said than done. That’s especially true if you’re learning exactly how your ignition system works in the process. If you have an older car, you’re likely going to be chasing wires. And those blessed with an OBD system can even be left scratching their heads trying to figure out exactly what’s going on if it only tells you that there’s a misfire and not why it’s misfiring. Or that there’s no power, but again, not why there’s no power.

A ballast resistor in an engine bay.
The Drive and its partners may earn a commission if you purchase a product through one of our links. Read more. ,  Hank O’Hop

Never fret, The Drive has its ignition mega-minds on the case and aren’t about to leave you on the lurch. We’re going to do our best to help you figure out what your problem is so that you can get on to the proper repair. Rubberized gloves ready?

Ignition Diagnostics Basics

Estimated Time Needed: 1-2 hours

Skill Level: Advanced

Ignition Troubleshooting Safety

Troubleshooting your ignition is a relatively harmless job, and it’s not likely you’ll get hurt if you practice common sense. Even so, you are working underneath the hood of the car, which may have a running engine. You are also working with a high-voltage system. That opens the door to the possibility of getting a nasty shock. So you’ll want to keep these safety tips in mind to avoid any unpleasant experiences.

  • Appease the OSHA Gods. I’ll admit that I’m often guilty of skipping the safety glasses and gloves, but it’s worth protecting the soft stuff when you’re working—no matter how unlikely getting injured seems.
  • Keep off the hot stuff. If your car will run and it has run recently, be mindful of the hot surfaces. Protective gloves will save your skin, but only from so much. Avoid contacting exhaust parts and even the intake with your bare skin.
  • Don’t get caught in the bug zapper. Whenever possible, disconnect the battery to prevent any electrical accidents. And if you’re using the old school methods of testing some parts, remember that the spark is looking for the easiest path to ground. Your flesh might be that path. Trust me, that ride isn’t fun.

Everything You’ll Need To Diagnose Your Ignition

The tools that you need for the job depend on the application. For most older cars, you’ll need little more than basic hand tools and a multimeter. Newer cars might need other tools and accessories. Again, it’s essential to do your homework on your application to verify if these or more tools are needed.

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.

Here’s How To Diagnose Your Ignition Issues

The first thing to understand is that ignition problems come in a variety of shapes and sizes, and that’s partly because different cars have different ignition systems and partly because there are various symptoms you may experience. In one case, your car might not start at all, and in another, it might start, but it runs rough. To further complicate things, the root cause in either situation isn’t always the same thing!

The point we’re making is that you need to treat every ignition problem as a case-by-case scenario. To that end, you need to familiarize yourself with the ignition’s components so that you can proceed accordingly. As with every how-to, that means there is some homework in order. Don’t start chucking wrenches yet, as no matter the type of vehicle you have, the basics of the troubleshooting system remain the same.

It helps to think of your ignition system as a chain. Your battery is the first link, and the spark plug is the final. Every other part, including the ignition module, distributor, and coil, are all the other links that connect them. Just like with a chain, if any of the links fail, the entire system falls on its face. In short, you’re trying to find out what the weakest link in the chain is when you’re troubleshooting your ignition by working from one component to the next until you’ve found it. So let’s get started.

1. Verify Lack of Spark

Whether it’s a misfire or a no-run condition, you want to make sure that lack of spark is your issue. To do so, you want to check to see if the spark plug itself is firing. With a misfire, start with the cylinder in question. With a no run, pick any plug you see fit. Next, test with either a spark plug test light or connect the plug to the ground and turn the key.

2. Check for Any Obvious Issues

It’s good to look for any obvious signs before breaking out the tools. For example, if you’ve just completed a project, likely, you’ve accidentally left something disconnected or bumped something along the way. Even if you haven’t worked on the car recently, it’s a good idea to make sure that there are no simple issues present.

3. Probe for Power

With the ignition on, break out the multimeter and check to ensure the adequate voltage is being supplied to the ignition system. If it isn’t, you’ll want to work back toward the battery to find out where your loss of power is, then correct the issue. Likewise, if you have a ballast resistor, you’ll want to ensure it’s supplying enough voltage to the system. 

Remember, the resistor’s job is to lower the voltage coming in. You’ll want to verify what the voltage coming out should be, then double-check it with the multimeter. If the results still aren’t clear, take a moment to check the resistance and verify that it is to spec.

4. Double-Check Firing Order

In the case of a no-run or misfire condition, it’s always worth verifying the firing order and checking it against your setup on the distributor cap. If you’ve just completed a project such as installing the distributor or plug wires, you may have things jumbled up. Don’t worry, it happens to the best of us.

5. Double-Check Initial Timing

If you’re working with a distributor, it’s worth verifying your initial timing. I know, it can be a pain to break out the breaker bar and line up your timing marks with your mind racing. But you might find that you’re 180 degrees out or that the distributor came off alignment due to a loose bolt on the hold-down clamp.

A close-up of a spark plug.
There are many ways to test a spark plug. If a quick visual inspection won’t tell you everything you need to know, you can place it on a grounded surface, crank the engine, and watch for spark. , Photo by Hank O’Hop

6. Test/Inspect Spark Plugs

If the firing order checks out or you don’t have a distributor, you’ll want to move to testing the plugs. If it’s a misfire, just focus on the spark plug in question. You’ll need to look for any signs of damage or fouling of the plugs. If nothing is obvious, you can test the plug with your multimeter.

A multimeter testing a spark plug wire.
Verifying plug wires are in check is as simple as testing the resistance. If there is any damage on the wires, they should be replaced anyway. , Photo by Hank O’Hop

7. Test Spark Plug Wires

When the plugs check out, it’s time to start working back through the chain by testing the links between. The first thing to inspect is your plug wires. Any signs of damage or decay are clear indicators that they’re your issue. To verify, you’ll want to check the resistance of the wires. That means you’ll need to check with the manufacturer of those wires to determine what your values should be, then verifying with a multimeter.

A close-up of a coil wire.
As with spark plugs, you can place the coil wire close to a grounded surface and crank the engine while watching for spark. , Photo by Hank O’Hop

8. Check for Spark at Coil

The next link in your chain to check is your coil or coil pack. Testing an external coil is simple. Simply remove the coil wire from the distributor and leave it connected to the coil. Then place the disconnected end near a ground, crank the ignition, and watch for spark.

An alternative is to check the resistance on the primary and secondary windings with the multimeter. As you can guess, the values you’re looking for depending on the manufacturer’s spec.

Testing a coil pack is made simple with the spark plug tester. If all else in the system checks out, but you still don’t have spark, the process of elimination tells us it’s the coil pack. 

A close-up of an open distributor cap.
Checking the cap and rotor requires a simple visual inspection. Any signs of severe wear on the contacts or damage to the components warrants replacement. , Photo by Hank O’Hop

9. Check Your Cap and Rotor

Checking the cap and rotor is an easy step that you can perform at any point so long as it is before you begin probing your distributor. The cap and rotor contain your contacts that are responsible for sending spark to the cylinders. All you want to make sure of is that the contacts within aren’t worn down or contain any obvious signs of damage.

10. Test the Distributor

The process of checking the distributor is dependent on the application you have to work with. An example is the 440 in my project Charger we’re probing today uses an electronic system that features a magnetic pickup. Testing is done by checking the resistance in the system at various points of the distributor’s cycle. Your process may be similar, but you’ll want to verify with the manufacturer of the distributor.

If you have points, the process is a little different. Namely, you’ll need to make sure that the breaker points aren’t worn down and that your condenser checks out.

11. Verify Distributor Settings

When the pickup and points check out, you’ll want to make sure your adjustments are correct. With an electronic setup, you’ll need to take the time to make sure the gap between the magnetic pickup and reluctor wheel is to spec. If you have points, you’re checking the gap between the breaker points contacts. 

A multimeter checking an ignition module.
The testing procedure for modules varies by application. In other words, plenty of homework is necessary if you don’t want to gamble on a replacement. , Photo by Hank O’Hop

12. Test the Ignition Module

At this point, we’ve checked everything, and we can almost conclude with absolute certainty that your ignition module, if present, is the issue. But that doesn’t mean you want to just spring for a new one. Instead, if possible, you’ll want to test the ignition module to verify it’s the issue.

The process of testing your module is heavily reliant on the model you have to work with. Make sure you do your homework to ensure you perform the proper test.

Pro Tips to Troubleshoot Your Ignition

  • Inspect and probe. Make sure there are no burnt or disconnected wires under the dash. Also, don’t rule out components like the starter relay and ignition switch as being the issue.
  • The starter might be the reason you don’t get spark during start-up. A lousy starter may soak up all of the voltage when turning your engine, and there won’t be enough juice to ignite the fuel and air mixture. You may have a similar issue if your battery isn’t powerful enough to meet the demand of cranking the motor.
  • Remember that spark isn’t everything. Compression and fuel are necessary to get the engine running. If you have a no-start issue and the spark checks out, you’ll want to make sure that you don’t have any problems in these departments.
  • Vacuum leaks can wreak havoc on your engine and even prevent the engine from firing off. Take a minute to make sure all of your vacuum lines are connected in a no-run situation.

FAQs About Ignition Diagnostics

You’ve got questions, The Drive has answers!

Q: What are the symptoms of a faulty ignition module?

A: Poor engine performance, misfiring, or no running conditions are all symptoms of a faulty ignition coil. In other words, the issues are the same as with any other faulty component in the ignition system. That’s exactly why troubleshooting is so important.

Q: What happens when an ignition switch goes bad?

A: A bad ignition switch can lead to a wide range of issues, including no spark. That said, you’ll want to make sure that all electrical connections to it are sound, that the contacts within aren’t bad, or that it doesn’t need to be reprogrammed.

Q: Can you overheat an ignition coil?

A: Yes. You can overheat your coil. Faulty plugs put a higher load on the system and can cause issues such as overheating. That’s why it’s important to also be mindful of where you mount a canister coil under the hood of your car.

Q: Can I drive with a bad ignition coil?

A: You probably can get the car to drive, but it’s not a good idea. Fuel and air are still entering the cylinder. Because the fuel isn’t burning, it will wash the cylinders and cause damage and eventually pollute the engine oil.

Q: How do you test for weak spark?

A: If you’re performing the old-school ground test, you just need to make sure that the spark is a strong blue color. You can also test the plug’s resistance to verify that it’s capable of supplying a strong spark.


Homework and the written word are overwhelming! We feel your pain! But we have you covered. This video provides a thorough breakdown of all the steps necessary for testing a conventional ignition system. Don’t have an older car? You’re not out of luck. Again, a lot of the basic principles of the testing procedure still carry over!

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Hank O'Hop Avatar

Hank O'Hop

Staff Writer

Hank is a Staff Writer at The Drive. He recently came to us as a freelancer with three years of industry-related experience and eventually earned his official title among our staff. As a self-taught gearhead, he spends the majority of his free time dissecting and playing with all things mechanical. He may be here to recommend tools and parts, but he's always happy to venture deep into the world of tech discussions and how-to guides, especially when it gives him the opportunity to display his beloved classic Dodge.