The ignition coil, or ignition coil, is an important part of a car's ignition system. The ignition coil supplies electricity to the spark plugs. There may be something wrong with the ignition coil if the car won't start, if the car doesn't run properly, or if the engine cuts out frequently. Fortunately, it is very easy to test yourself whether the ignition coil is functioning properly. Based on the results, you can determine whether or not you should take the car to the garage.
Method 1 of 2: Test the ignition coil with a spark test
Step 1. Turn off the engine and open the hood
Apply the parking brake and turn off the engine. Open the hood and look for the ignition coil. The exact location varies by car, but you can usually find the ignition coil at the rear of the engine compartment or under the hood of the distributor. On cars without a distributor, the spark plugs are connected directly to the ignition coil.
- A good way to locate the ignition coil is to follow the wire from the distributor that does not lead to a spark plug.
- For your own safety, wear safety glasses and gloves and use only insulated tools to avoid shock.
Step 2. Remove a spark plug wire from the spark plug
Normally the cables run from the distributor to the various spark plugs.
Step 3. Remove the spark plug with a spark plug wrench
After you have removed the spark plug wire you can remove the spark plug. The best way to do this is with a special spark plug wrench.
- If your engine has been running for a long time, the various components will be very hot. If that is the case, it is better to let the engine cool down for 5-10 minutes before starting.
- To save time and prevent your spark plug from getting damaged, consider using a spark plug tester instead. Instead of reattaching the spark plug to the wire, attach the spark plug tester to the wire. Ground the clamp. Have your friend start the engine and watch for sparks in the opening of the tester.
- Using a spark plug tester also means you don't expose your combustion chamber to dirt.
Step 4. Remove the spark plug using a spark plug cap
Once you have removed the spark plug wire, remove the spark plug itself. This is easiest with a specialized socket wrench called a spark plug cap.
- From now on, make sure that nothing falls into the hole created by removing the spark plug. If something falls into the cylinder head hole, it can seriously damage the engine, and it is very difficult to remove anything that has fallen in. So make sure nothing falls in.
- Cover the cavity with a clean cloth or towel to prevent dirt from entering the combustion chamber.
Step 5. Reattach the spark plug to the spark plug wire
Now you have a spark plug connected to the distributor, but no longer stuck in the cylinder head. To avoid shock, grasp the spark plug only with insulated tools.
Step 6. Allow the threaded portion of the spark plug to contact metal of the engine
You move the spark plug with the pliers (with the cable still attached) so that the threaded 'head' makes contact with a metal part of the engine. That can be any part of the engine block - even the engine itself.
- Never touch the spark plug with your hands, but use insulated pliers (and wear gloves). If you don't, you run the risk of electric shock in the following steps.
- Failure to remove the fuel pump relay means that the cylinder under test will not fire because there is no spark plug. However, it will still be flooded with fuel, which can cause serious damage.
- Refer to your manual to locate the fuel pump relay.
Step 7. Ask someone to turn the ignition key
Have someone turn the ignition key without starting the car. Now the car's electrical system is activated and current is applied to the spark plug that you hold with the pliers (assuming your ignition coil is working).
Step 8. Check for blue sparks
If your ignition coil is working properly, you will see blue sparks when the ignition key is turned, near the electrodes on the spark plug. This spark is clearly visible in daylight. If you don't see a blue spark, your ignition coil is probably bad. This must then be replaced.
- Orange sparks are a bad sign. This indicates a lack of electricity being delivered to the spark plug (which can be caused by a number of reasons, including cracks in the ignition coil housing, not enough power, bad connections, etc.).
- If you don't see any sparks at all, either the ignition coil is completely broken, the electrical connections are bad, or you did something wrong in your test.
Step 9. Place the spark plug back into the cylinder head and attach the spark plug wire
When you have finished your test, the contact should be turned off again. Then you can perform the steps in reverse order. Disconnect the spark plug from the spark plug wire, tighten the spark plug into the hole with a spark plug wrench and reattach the spark plug wire.
Congratulations! You did a spark test to test your ignition coil
Method 2 of 2: Test the ignition coil by measuring the resistance
Step 1. Remove the ignition coil from the car
The test described above is not the only way to test the operation of the ignition coil. If you have access to a resistance meter or a multimeter, you can measure the resistance of the ignition coil. From this you can objectively deduce whether your ignition coil is working properly, which is better than the somewhat subjective method from the first section. But to measure the resistance you must first remove the ignition coil from the car.
Read your vehicle's service manual for precise instructions on how to remove the ignition coil. Usually the ignition coil must first be disconnected from the distributor cable, then the ignition coil must be loosened with a spanner or ring wrench. Your engine must be off before you start
Step 2. Find the correct resistance values of your coil
Each coil has unique specifications in terms of electrical resistance within the coil. If the measured resistance does not fall within these values, there is something wrong with the ignition coil. In most cases you can find the values in the service manual of your car. But if you can't find it there, you can check with the dealer or search online.
In general, the primary coil should have a resistance value of between 0.7 and 1.7 ohms, the secondary coil should give a value of between 7500 and 10500 ohms
Step 3. Place the pins of the multimeter on the terminals of the primary coil
The distributor has three electrical contacts - one on each side and the third in the middle. These contact points can be protruding or recessed - it doesn't matter. Turn on the multimeter, set the multimeter to measure resistance and let the two pins make contact with the outer contacts. Write down the reading - this is the resistance of the primary coil.
Some newer ignition coils have different contact points. Check the service manual for further information if you are not sure which contacts correspond to the primary coil
Step 4. Place the pins of the multimeter on the terminals of the secondary coil
Hold one pin against one of the outer contacts and hold the other pin against the middle contact (where the main cable from the distributor is connected. Write down the measured value - this is the resistance of the secondary coil.
Step 5. Determine whether the measured values fall within the normal values for your type of ignition coil
Ignition coils are delicate components of a car's electrical system. If the readings from the primary or secondary coil fall outside normal ranges, even just slightly, then the coil is damaged or malfunctioning. In that case, the ignition coil must be replaced.