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How To Test Ignition Coils



author By Anna Finger
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Preparation for Ignition Coil Test

Ignition Coil

The first thing you want to do is always take the necessary precautions. When working near or around a running engine one must exercise great caution. You should be aware of any loose clothing. If you have long hair you want be careful that it does not make contact with any part of your car's engine and its moving parts.

Testing the ignition coil on your car is one of the fairly easier tasks to perform. It's not that complex nor does it require any special tools or equipment. One thing to keep in mind is that your ignition system produces a great amount of electricity. Should anything go wrong, the result could be very dangerous. Proceed cautiously.

If your coil has already been removed from your vehicle and you need data that is more specific about your ignition coil, you can perform what is called a bench test. Set up the bench test by removing the one spark plug wire from its plug. Then remove the spark plug with a plug socket. Now you want to connect that spark plug back to the spark plug wire. Do this with great care; you don not want anything to fall into the empty spark plug opening or you'll have a problem.

Testing the Ignition Coil: The Bench Test:

Grab a pair of insulated pliers. Hold your plug wire with insulated pliers. Now, you need a grounding point so look around your engine for one. You want a spot that is easy to access and that has exposed metal. You could even use the car's engine for this.

Bench Test

Hold the spark plug wire with your insulated pliers and make contact with your chosen grounding spot with the threaded part of your spark plug. Have some one start your car's engine and pay attention to the spark plug gap. You are looking for a bright blue spark to jump across the gap - the electricity. If you can observe this blue spark clearly, even in daylight, then your spark plug is working just fine.

Testing the Ignition Coil: The Multimeter Test

There are a number of other tests you can perform for your ignition coil. However, if you want accurate information on the status of your ignition coil then you should perform a multimeter test. This test is far more accurate in determining whether you need to replace the coil or not. It is considered the only proper test for a coil.

You could rely to an extent on the bright blue spark you see in your bench test but if that spark is somewhat weak and your eyes can't really tell, using this spark plug can cause your vehicle to run rough or incorrectly which is the last thing you want.

Multimeter Test

Let go inside the ignition coil for a moment. The ignition coil contains two coils of wire that are right on top of each other. We refer to these coils as windings. There is a primary winding, the first wire, and a secondary winding, the second wire. The primary winding collects the electricity to create the spark. The secondary winding sends it out to the distributor. It is possible for either of these windings to malfunction causing your vehicle's ignition coil to fail. Sometimes an ignition coil can completely fail meaning it makes absolutely no spark whatsoever.

A multimeter test is performed with the ignition coil completely disconnected. This meter provides numbers to help you determine the status of the coil - far more reliable than a visual assessment. There are different types of digital multimeters and they can be found online or at your local auto repair retailer.

Of course, to use the multimeter, you will have to know the resistance specifications for your ignition coil. If you don't know what they are then refer to your vehicle's service or repair manual for that information.

Testing the Windings

To test the primary winding of your ignition coil:

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As mentioned above, the primary winding of the ignition coil first collects the electricity or voltage from the car's battery. Have you found the resistance specification for your ignition coil? You will need this before performing the multimeter test. If you do not have them take a moment to locate you service or repair manual for that information.

Once you have found the resistance specifications, locate your digital multimeter. If you have a traditional round coil, you will need to use the multimeter and place the leads on the small, outside poles of your ignition coil. If you have one of the newer enclosed units, then place the leads on indicated or marked poles of your coil.

Observe the reading you get on the multimeter. If the multimeter reads within the range according to the specification in your service manual, then your primary winding is functioning well and you can go on to check the secondary winding. If you find the reading to be even slightly out of the range then you should replace the ignition coil.

To test the secondary winding of your ignition coil:

The secondary winding of your ignition coil sends the spark to your distributor and then to the spark plugs. A weak spark or no spark at all is an indication that the coil needs to be replaced.

To test your ignition coil's secondary winding, attach the probes to the outer 12V pole and the center pole of your ignition coil. The center pole is the spot where the main wire is located that connects to the distributor. Again, check the reading to make sure they fall within the specified range as indicated in your car's service manual. If your coil falls within that range all is well. If the reading should fall even slightly out of the specified range, then you should replace your ignition coil. Remember a failing ignition coil will cause your engine to run rough and can cause other problems as well.