Procedure for Diagnosing and Testing an Ignition Coil

Engine Related Issues

By Rodney (Mechanics)

Ignition coils are basically the batteries for your spark plugs. They send the power the spark plugs need to operate. Cars usually have one coil but the some ones have two. The ignition systems also come in several types. There are those who fit one coil for every two cylinders, while the others have one coil for each spark plug cylinder.

Envisage the ignition coil as a power generator. It takes the 12V from the car’s electrical system and turns it into the power of thousands of volts.

There are a few things that affect the amount of power needed: size of the gap on the spark plug, the resistance of the spark plug and wires, how the air/fuel mix is, the engine load, and the temperature of the spark plug. However this voltage can change and it can be from 5,000 up to 25,000 volts or even more. Some systems output as much as 40,000 volts when that is necessary.

Procedure for Diagnosing and Testing an Ignition Coil

Here’s How An Ignition Coil Works

Inside every ignition coil are two sets of wires wrapped around an iron core. The first set of wires, called the “primary” windings, are connected to the battery and the ignition module. The second set of wires, called the “secondary” windings, are connected to the primary wires and the high voltage output in the center of the ignition coil.

The more secondary windings there are compared to primary windings, the higher the voltage the ignition coil can produce. Performance ignition coils typically have more windings than standard coils.

When the part that controls the spark plugs connects to the ground, electricity flows through the first set of wires. This makes a strong magnet around the metal core and fills up the ignition coil with power. It takes a very short time for the magnet to become as strong as possible.

The part that controls the spark plugs then disconnects the first set of wires. This makes the magnet disappear quickly. The power stored in the magnet has to go somewhere so it creates electricity in the second set of wires. This increases the voltage until there is enough voltage to make the spark plug work.

Ignition Coil Test for Coil-On-Plug Systems

Ignition Coil Failures

Ignition coils are usually very good, but they can break. Heat and shaking can hurt the ignition coil’s wires and covering causing breaks or gaps in the wires. But the main reason for ignition coils breaking is too much voltage caused by bad spark plugs or wires.

If the wire or a spark plug is broken or has too much resistance, the output voltage of ignition coil’s can go up to the point where it burns through the ignition coil’s covering causing a break. Once this happens, the ignition coil’s output voltage may go down causing the engine to work poorly when it needs more power, or the ignition coil may stop working completely preventing the engine from starting or running.

If a coil has battery voltage at its positive end and is being connected and disconnected by the part that controls the spark plugs or circuit but is not making a spark, the ignition coil is broken and needs to be changed.

Note: If the part that controls the spark plugs has broken more than once, it may be because of a bad ignition coil. Sparks or breaks inside a coil can overload and damage the parts inside the part that controls the spark plugs.

Check The Ignition Coil For A Spark

Ignition Coil Diagnosis

When the ignition coil, which helps start your car, fails in a traditional system, it affects all the cylinders (parts of the engine). Your car might not start, or it might run poorly. The problem could also jump from one part of the engine to another. But in a newer system, a single coil failure will only affect one part of the engine.

If your engine is misfiring with a Check Engine Light on, scanning ignition codes is a good tool to use. These codes signify that the engine components aren’t firing the way they should.

With the newer engines a coil failure usually lights up a particular misfire code. Take for example an engine P0301 error which will tell you the numbers one starts to misfire. A misfire occurs if a mistake happens in ignition, fuel, or compression, so do not treat a misfire as bad coils, spark plugs, or plug wires. Another possible cause could be the injector is not performing well or there is a leak in the engine.

Diagnosing and Testing an Ignition Coil

So, a code setting may also be done when the ignition coil is broken or open in this particular part of the engine. If there is no code, take the ignition coil resistance and measure it via a digital meter. Removal of the spark plug and examination is also important. Watch for the spark gap and examine the plug deposits to see if the misfire here is caused by any buildup. Also check the plug wire (if there is a one then) to make sure the wire’s resistance is not over the specifications.

If the ignition coil, spark plug and plug wire seem to be functioning properly the misfire could be caused by the fuel injectors being dirty or dead. Measure the injector resistance and the voltage supply, and a light for testing if there is a pulse from the driver circuit. If injector works, do a compression check to make sure pneumatic valves or head gaskets are not leaky.

Note: The engine turns but does not start. It is not because of the ignition coils. It is because there is no spark. More likely, the fault is a bad position sensor, a voltage supply problem to the ignition coils in the ignition circuit, a bad ignition module, or a bad driver circuit in the engine control unit.

Checking Your Car’s Ignition Coil Is Working or Not

Before you start, be careful: “Keep your hands away from the wire that connects the ignition coil to the spark plug.” There is a lot power is it can shock or breakdown the ignition coil. The correct way to check if a spark is present inside the cylinder is by using a special tool known as “spark plug tester”.

If you doubt whether the ignition coil is operational, you can measure electric power via meter, called Ohm meter. If it doesn’t match the required number, you should replace the ignition coil.

You can easily check the ignition coil with a digital ohmmeter that has 10 megaohms. Look at your car’s manual to see what the number on the ohmmeter should be, because it can be different for different cars.

To verify the ignition coil, get the contacts of the ohmmeter attached to the two metallic parts of the ignition coil (+ and -). The majority will be around 0.4 and 2. If the number is zero, it means that the fuse is blown. If well number is high, this means that coil is open.

The probing of the remaining part of the ignition coil is possible by getting the ohmmeter to the positive (+) terminal and the other side that is going to the spark plug. Newer coils usually have numbers varying from 6,000 to 8,000, whereas the old coils can have up to 15,000.

Some coils are not shaped like a can, and the metal parts may be hidden in a plug or under the ignition coil. Look at your car’s manual to see where they are and how to check them.

How To Test The Ignition Coil

Another Way To Check The Ignition Coil

Another way to check the ignition coil is to use a tool called a “spark tester.” You can buy one online or at a car parts store. It goes between the ignition coil and the spark plug. With the engine OFF, unplug the ignition coil from the spark plug, connect one end of the spark tester to the spark plug, and connect the other end to the ignition coil.

After you have set up the spark tester, start the engine. If the spark tester has a light that flashes, it means the ignition coil is making electricity and the part that controls the ignition coil is also working. If the engine is not running smoothly, the spark plug may be dirty, cracked or not working. If the light does not flash, it means the ignition coil or the part that controls it is bad. Check the wire that connects the ignition coil to see if it is loose or rusty. A bad wire can stop a good coil from making a spark.

How To Test The Ignition Coil

A part of the car stores has an appliance that is capable of testing the ignition coil. It can simulate the behavior of the working coil when the engine is turned on. The test is the indicator of the correct operation of the ignition coil. In case your coil passes the test but your engine doesn’t run smoothly, the problem could be a dysfunctional spark plug, a break connection at the ignition coil or a faulty part in your computer. The coil which did not complete any part of the test should be replaced by a new coil.

Ignition Coil Terminals Resistance Table

A Bad Ignition Coil Can Break The Car’s Computer

When this ignition coil has a problem and has less electricity than normal, it will allow too much energy go through it. This may result in the damage of the car’s computer section which controls the ignition coil. The operating temperature may also reduce the ignition coil electricity which will generate a weak spark and make you start the engine slowly; speed up the engine or even stop the engine when you speed it up.

The coil that is the problem because probably it has excessive electricity or no electricity at all in the first part of the ignition coil may not break the part of the car computer system that regulates the ignition coil. It will result in the second part of the ignition coil getting less electricity or no electricity.

If the part of the ignition coil, which is the weak one, produces abnormal current, the spark produced by it will be weak, but it will not damage computer part responsible for control of the ignition coil.

If it is found that the ignition coil has a flaw that makes it provided more electricity than usual or even no electricity in the second part of the ignition coil, it will also make a weak spark or no spark. It can also cause damage to the part of the car computer which controls the ignition coil; this occurs because of the electricity that goes back to the first coil.

Change Ignition Coil

How To Change The Ignition Coil

When you need to change the ignition coil, you should use a new coil that is the same as the old one. Unless you want to make your ignition system better with a stronger coil.

When you change the ignition coil, you should clean the connectors and make sure they are not rusty or loose. Rust can make the ignition coil work poorly or not at all. You should also put some grease on the connectors that go to the spark plugs to keep them from getting wet. Wetness can make the spark jump to the wrong place. This is a common problem for Ford trucks with COP coils.

If the ignition coil keeps breaking, it may be because it is doing too much work. The reason may be that the spark plugs are old or too far apart, or that the engine is not getting enough fuel (because of dirty injectors, air leaks or a bad EGR valve).

If the engine has a lot of miles and has COP coils, you should also change the spark plugs if the ignition coil breaks. This is true if the old plugs are normal plugs with more than 45,000 miles on them, or long-life plugs with more than 100,000 miles on them.