Are you having problems with your ignition system?
Is your car misfiring any time you try to accelerate, or the engine simply fails to start?
If your answer to these is yes, then your ignition coil may be the problem.
However, for individuals using older cars, this diagnosis process becomes more intricate, as coil packs are used in place of the contemporary distributors.
Our guide presents you with all you need to know about how to test coil pack with multimeter.
Let’s get started.
What Is A Coil Pack
A coil pack is a type of ignition coil system common within older cars where multiple coils are mounted on a single unit (pack) and each coil sends current to one spark plug.
It is a Distributorless Ignition System (DIS), also called the wasted spark system, which boycotts the need for a distributor, as the pack somewhat serves as the distributor itself.
The ignition timing from each coil is controlled by the ignition control unit (ICU), with one coil terminal firing on the compression stroke of its cylinder and the other terminal wasting on the exhaust stroke of another cylinder.
Apart from all these, the coil pack works like any typical ignition coil. Each coil on it consists of two input windings and a single output winding.
The two input windings receive 12 volts from the battery, twist around the output winding, and the output winding shoots 40,000 volts or more to the spark plugs to ignite the engine.
These components may go bad and cause certain discomforts like the engine misfiring, rough idling, or completely failing to start.
Sometimes, these symptoms may be caused by a component that works with the pack and not the pack itself, like the ignition module.
This is why you need to run tests on the coil pack to properly diagnose where your problem is coming from.
If you make use of a magneto coil rather than a regular ignition coil, then you may look at our article on diagnosing a magneto coil.
Tools Required To Test Coil Pack
To run all the tests we mention here, you’ll need
- A multimeter,
- Multimeter probes,
- A wrench, or a ratchet and socket, and
- A new pack.
How To Test Coil Pack With Multimeter
To diagnose a coil pack, set the multimeter to the 200 Ohms range, place the positive and negative probes on the identical terminals of a coil, and check the multimeter for a reading. A value between 0.3 ohms and 1.0 ohms means the coil is good, depending on the model.
This is only a quick run-through of how to diagnose a coil pack by testing its primary resistance.
We will dive deeper into each step in this testing procedure, additionally show you how to test secondary resistance, and present other ways of diagnosing a coil pack in your vehicle.
- Locate The Coil Pack
With your car engine powered off, you want to find where the ignition coil pack is located within your engine and take it out to comfortably run tests on it.
Referring to your engine manual is the easiest way of spotting where the pack is situated.
However, if you don’t have a manual with you, you may simply trace where the engine spark plug wires lead to.
The spark plug is located on the top or side of the main engine, so you follow where the wires lead to.
The coil pack is typically located on the back or side of the engine.
- Take Out The Coil Pack
To take the unit out, you remove the spark plug wires from the coil terminals. Remember that there are multiple coils on a coil pack.
You detach spark plug wires from the output tower terminal of each of these coils on the pack.
While disconnecting the wires, we advise that you label each so they are easier to identify and map out when you are reconnecting them.
Finally, you remove the pack’s electrical connector, which is a peculiar wide connector going into the main pack body.
Now, you take out the pack using a wrench or, in some cases, a ratchet and socket. Once it is out, move to the next step.
- Set The multimeter To 200 Ohms Range
To measure the resistance of the primary input windings of each coil in the pack, you set the multimeter to the 200 Ohms range.
The Ohms setting is represented by the omega symbol (Ω) on the meter.
- Place Multimeter Probes On Primary Terminals
The input terminals are the two identical tabs that either look like bolts or bolt threads. They connect to the primary windings within the coil.
Each coil in the pack has these terminals and you want to make this placement to test each of them.
- Check Multimeter
Once the multimeter leads make proper contact with these terminals, the meter presents a reading. Generally, a good ignition coil is expected to present a value between 0.3 Ohms and 1.0 Ohms.
However, your engine model specifications determine what the right resistance measurement is. If you get an appropriate value, then the coil is good and you move to test each of the other coils.
A value outside the appropriate range means that the coil is bad and you may need to replace the whole pack.You may also get an “O.L” reading, which means there is short within the coil and it should be replaced.
Now, we move to steps for testing the secondary resistance.
- Set The Multimeter To 20kOhms Range
To measure the ignition coil’s secondary resistance, you set the multimeter to the 20kOhms range (20,000 Ohms).
As mentioned before, the ohms setting is represented by the Omega symbol (Ω) on the meter.
- Place The Probes On Coil Terminals
The output terminal is a single and distinct protruding tower that connects to the secondary winding within the ignition coil.
It is the terminal to which your spark plug wires were connected before you detached them.
You will be testing each of the input terminals against the output terminal.
Place one of your multimeter probes into the output tower to make contact with a metal part of it, then place the other probe on one of your input terminals.
- Look At Multimeter
At this point, the multimeter presents you with a resistance value.
A good ignition coil is expected to present you with a general value between 5,000 Ohms and 12,000 Ohms. Since the multimeter is set to the 20kOhms range, these values are between 5.0 and 12.0.
The appropriate value depends on the specifications of your ignition coil model.
If you get a value in the appropriate range, the terminals of the coil are in good condition and you move to other coils.
If you got a value outside this range, then one of the terminals is bad and you may need to replace the whole coil pack.
An “O.L” reading means there is a short within the coil. Remember that you test each primary coil against the output coil.
Testing Spark Power
Another way of testing a coil pack for issues is to verify if each of its coils is producing the right amount of voltage to power their respective spark plugs.
This helps to clear the air about the problem if your engine starts but misfires when you attempt to accelerate.
For this, you will need an ignition coil tester. There are different types of ignition coil testers which have varying methods of application.
The most common are the inline ignition tester, the ignition spark tester, and the COP ignition tester.
The inline ignition tester serves as a connector wire that links the coil’s output tower, where the spark wire normally goes into, to the spark plug.
When ignition is initiated, this tester shows you a spark, helping you determine if the coil is producing one or not.
The ignition spark tester, on the other hand, is used in place of the spark plug and shows you a spark if it’s receiving one.
Lastly, the COP ignition tester is an inductive tool that helps you measure spark within a coil-on-plug system without having to remove the coil or spark plug.
Testing By Swapping
The easiest and most expensive method of diagnosing a coil pack for issues is to simply replace it with a new one.
If you replace the whole pack with a new pack and your vehicle starts working perfectly, then you know that the old pack had issues and your problem is fixed.
One other simple way of diagnosing an ignition coil for issues is to visually inspect it, and also components connected to it, for physical damages.
These physical signs come in the form of burn marks, melting, or cracks on the coil pack, spark plug wires, or electrical connector. Leaks from the coil pack may also signal that it has gone bad.
Testing the ignition coil pack in your vehicle for fault isn’t as hard as you may have thought.
The most important keynotes of the test is to make sure the multimeter is set up properly and the probes are placed on the right terminals.
Frequently Asked Questions
How Do I Know If My Coil Pack Is Faulty?
The signs of a bad coil pack include engine misfiring, the check engine light illuminating, rough idling, or the engine entirely failing to start. A multimeter may also be used to look for faults.
How Do You Check The Power Of A Coil Pack?
To identify if a coil is firing enough spark, you need an inline ignition tester or an ignition spark tester mounted as a spark plug. These allow you to safely measure spark from a coil.
Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.