In this guide, you will learn how to check if spark plugs are getting power.
The easiest and safest way to check for spark by yourself is to use an inline spark plug tester.
Alternative methods to test an engine for spark include removing the spark plug and grounding it or testing for spark with a screwdriver.
- When you test your ignition system for spark, keep your hands off ignition coils, wires, or spark plugs while cranking the engine. Ignition coils generate on average 30,000 volts, enough to cause injuries and shock.
- If you will be cranking the engine for an extended period to test your car for spark, keep a backup battery source connected to avoid draining the main car battery.
How to test for spark
Checking if you are getting an ignition spark with a test light is quite simple. Plug the spark plug inline tester between the spark plug and the ignition coil.
Remove engine cover
If you have a vehicle model year 2000 and newer, it will most likely have an engine cover. Remove the cover by lifting it. Engine covers are held in place with tabs.
Locate the spark plugs
On a four-cylinder engine, the spark plugs will be right on top of the engine. This is typically true for inline-six engines as well. If your car is a V6, then you will have three cylinders on one side of the engine block and the other three on the other side.
Disconnect the injector
We don't want to flood the engine with fuel. Therefore as a best practice, it is recommended to unplug the electrical connector from the fuel injectors or remove the fuel pump's relay.
If you check only one of the cylinders for a spark for a couple of seconds, you may be fine without disconnecting the spark plugs. If you crank the engine for an extended period of time with the injector connected, you will flood the cylinders with gasoline, which can foul the spark plugs.
Remove the ignition coil.
Remove the ignition coil from the spark plug that you want to test. Unplug the ignition coil from the spark plug but keep it connected to the wire harness.
Connect spark plug tester
Connect the inline spark plug tester in between the ignition coil and the spark plug. One end of the spark plug testers fit on the ignition coil, and the other on top of the spark plug.
Check for spark
Set the spark plug tester aside. Now it is time to check if your engine is getting a spark. Keep your hands away from the ignition coil and the spark tester. Have a helper turn on the ignition and try to start the engine.
As the engine turns over, look if there is a spark on the test light. If there is a small light flashing, it means you are getting a spark. If your car doesn't start, you may have a fuel related issue, timing issue. Also, check for bad spark plugs.
If there is no light at all at the test light, you are not getting a spark.
How to check for spark with a screwdriver
High voltage. Risk of injury. This method is not recommended.
A quick and dirty method of checking for spark is using a screwdriver.
Locate spark plug
You will need to pop the hood open. Remove that large engine cover and find the spark plugs.
Remove spark plug wire or ignition coil.
If you have a newer car, you will most lily have an ignition coil on top of each spark plug. Remove one of the ignition coils. If you have plug wires, remove one wire from the spark plug.
Connect screwdriver to test for spark
Stick your screwdriver into the ignition coil or the plug wire boot.
Place screwdriver near the engine block
Place the screwdriver about 1/8" from the engine block. While someone else cranks the engine, you should closely examine the gap between the engine and the screwdriver. If your ignition system is working properly, you should see a spark here.
If your spark plugs aren't firing, then you won't see a spark here. Which means you have an ignition problem you need to address.
Test for spark with no tools
Another method to check if you are getting spark plugs is to remove the spark plug from the engine.
Plug it back on your ignition coil or spark plug wire and ground the threaded part of the spark plug to the engine block.
Make sure you unplug the injector or remove the fuel pump relay. As you crank the engine, you should see a small spark at the tip of the spark plug.
There are several other ways to check a car engine if it is getting a spark. You can check for spark using a multimeter, test light, screwdriver, or even remove the spark plug and ground it on the engine block or frame.
What to do if your car won't start
engine cranks, but it will not start, and you have already verified that the engine is getting a spark? The problem could be any of the following:
- No fuel or low fuel pressure
If your engine is not getting fuel, your car engine will not start. Check for fuel pressure. Check fuel pump operation.
- Ignition Module Defective
If your vehicle is equipped with an ignition module, it is possible that it can be bad.
- Bad Crankshaft Position Sensor (CPS)
On newer vehicles, the crankshaft position sensor plays a key role in determining the crankshaft position. If it fails, you will notice intermittent starting issues. Typical symptoms include car starts fine when cold, but when it warms up. The CPS sensor's problem is that it may not even trigger the check engine light on in some cases.
- Timing Issue
If there is a timing issue and valves don't close when the pistons hit Top Dead Center (TDC), your car won't start.
- Low compression
Low cylinder compression can also cause no-start conditions.
If you are getting spark at all ignition coils except one of them, the most lily cause is a bad ignition coil or a cut wire for that particular ignition coil.
The methods described here helps you learn how to check for ignition spark. If your car doesn't start, it is important to look at other possible fuel pressure issues. This guide only shows you how to check if the spark plugs are firing, nothing more.
While these instructions were meant to help learn how to check for spark on a car engine, these methods can check for spark on lawnmower and motorcycles as well or any large or small gasoline engine.
How to check if a spark plug is firing without a test light?
An alternative method to check if a spark plug is firing is to remove the spark plug from the engine. Plug the spark plug on your ignition coil. Ground the threaded part of the spark plug to the engine block. Crank the engine and see if you are noticing any spark at the spark plug tip.
How do I know if I need new spark plug wires?
- Most owners realize they need new spark plug wires when their car starts to miss fire, struggle to accelerate uphill, or sets the check engine light with codes such as P0300 P0301 P0302 P0303 P0304 P0304 P0304.
- There are ways to tell if you need new spark plug wires. Use an insulated screwdriver and move it along the spark plug wires (at least two wires). Do you notice any arc from the wire to the screwdriver? If you do, it means you need new spark plug wires.