The ignition coil is a very important component in the ignition system of every vehicle which is responsible for providing electricity to the spark plugs. When the vehicle does not start and breaks down frequently, the ignition coil may need to be replaced. Luckily there is a relatively quick and easy test that can determine if the ignition coil is functioning properly and whether you need to go to a vehicle parts store or mechanic's garage. See Step 1 below to get started.
Step
Method 1 of 2: Performing the Ignition Coil Spark Test
Step 1. Turn off the vehicle and open the hood
As with most types of vehicle maintenance, you should start the test with the vehicle on the road and with the engine off. Open the hood to find the ignition coil. While the exact location may vary for each vehicle, generally the ignition coil is located near the fender or bolted to a bracket near the distributor. It should be noted that in vehicles without a distributor, the spark plug will be connected directly to the coil.
- One surefire way to find the ignition coil is to look for a distributor and follow the wires that are not connected to the spark plug.
- Before starting, make sure you wear safety glasses or other eye protection and that you have insulated tools (especially pliers) to protect against electric shock.
Step 2. Remove one spark plug wire from the spark plug
Next, remove one of the spark plug wires from the spark plug. Usually this wire runs from the distributor cap to each of the spark plugs. To prevent injury, be careful when working on your vehicle's electrical system. Use insulated gloves and tools at all times.
- If your vehicle has been running for some time, its internal components will most likely be very hot. Vehicles driven for at least 15 minutes can heat up the engine to about 200 degrees. Allow the vehicle for an hour to cool to prevent significant injury.
- To save time and avoid damaging your spark plugs, consider using a spark plug tester. Instead of reattaching the spark plug to the wire, attach the spark plug tester to the wire. Ground the alligator clamp then switch straight to it and ask your friend to start the engine and see the sparks in the tester gap.
- Using a spark plug tester also means you won't be exposing the combustion chamber to dirt.
Step 3. Remove the spark plug using the spark plug socket
Once you have removed the spark plug wire, remove the spark plug. This is easily done with a special socket wrench, the spark plug socket.
- From here on out, be careful not to drop anything into the empty hole left by the spark plug. Leaving dirt in these holes can cause damage to the engine while the vehicle is running so it is better to prevent this from happening as it will be difficult to clean anything from these holes.
- Cover the hole with a clean cloth or towel to prevent dirt from entering the combustion chamber.
Step 4. Reattach the spark plug to the spark plug wire
Carefully put the spark plug back into the wire. You should leave the spark plug connected to the distributor, but not in the hole. Hold the spark plug with insulated pliers to avoid possible electric shock.
Step 5. Contact the threaded part of the spark plug against the exposed metal of the engine
Next adjust the spark plug (the wire is still attached) so that the threaded head of the spark plug is in contact with some of the engine metal. This can be solid metal parts of the engine block and the engine itself.
Again grip the spark plug carefully using insulated pliers (and gloves if possible). Don't risk electric shock in the next few steps by ignoring these easy safety precautions
Step 6. Remove the fuel pump relay or fuse
Before you start the engine to test the spark plugs, you must turn off the fuel pump. Once this is done, the engine will not start so you can test the coil for sparks.
- Not removing the fuel pump relay means the cylinder being tested will not spark because there is no spark plug. However, the cylinder will still be flooded with fuel which can cause serious damage.
- Check your manual for the fuel pump relay.
Step 7. Ask a friend to start the engine
Ask a friend or assistant to turn the key on the vehicle's ignition. This will provide power to the vehicle's electrical system and to the spark plugs you're holding (assuming your ignition coil is working).
Step 8. Look for the blue sparks
If your ignition coil is functioning properly when your friend starts the engine, you should see a bright blue spark jump through the spark plug gap. These blue sparks will be clearly visible during the day. If you don't see blue sparks, your ignition coil is probably malfunctioning and needs to be replaced.
- Orange sparks are a bad sign. This means that the ignition coil is not supplying enough electricity to the spark plug (for various reasons such as cracked coil sheath, weak electric current, faulty connection, etc.).
- The last possibility you can observe is the absence of sparks. This is usually a sign that the ignition coil is completely malfunctioning, one or more of the electrical connections is faulty, or that you made a test error.
Step 9. Carefully reinstall the spark plug and reconnect the wires
When you have finished testing, make sure the vehicle is turned off before repeating the above preparation steps in reverse order. Remove the spark plug from the wire, reinsert the spark plug into the hole, and reconnect the wire.
Safe! You have completed the ignition coil test
Method 2 of 2: Performing the Ignition Coil Resistance Test
Step 1. Remove the ignition coil from the vehicle
The tests above are not the only way to determine if the ignition coil in your vehicle is functioning properly. If you have an electrical ohmmeter that measures electrical resistance, you can measure the effectiveness of your ignition coil in a precise and measurable way rather than the method described above. However, to start this test, you must remove the ignition coil of the vehicle so that you can easily access the electrical terminals.
Refer to your maintenance manual for accurate instructions for removing your ignition coil. Usually you need to remove it from the distributor cable and then remove it from the holder using a socket wrench. Make sure your vehicle is turned off and cool before starting the process
Step 2. Find the resistance specifications for your ignition coil
Each vehicle ignition coil has specific specifications for the electrical resistance in the coil. If the actual resistance level of your coil is outside these specifications, you will know that your coil is damaged. You will usually find the resistance specifications specific to your vehicle by looking at your maintenance manual. If you can't find it there, you can contact your dealer or search for vehicle resources online.
Generally vehicle coils will have resistance readings of around 0.7 – 1.7 ohms for the main coil and 7,500 – 10,500 ohms for the secondary coil
Step 3. Place the lead of the ohmmeter on the pole of the main coil
The distributor will have three electrical contacts i.e. two contacts located on each side and one contact located in the middle. These electrical contacts can be external (protruding) or internal (concave in). Turn on your ohmmeter and hold one end to each outside electrical contact. Record the resistance reading which is the resistance of the main coil of the coil.
Note that some newer ignition coil models have a different contact configuration than the traditional arrangement. Refer to your vehicle's manual for information if you are not sure which contact fits the main coil
Step 4. Place the lead of the ohmmeter on the pole of the second coil
Then hold one end to one of the outer contacts and hold the other end to the middle and inner contacts of the ignition coil (where the main wire connects to the distributor). Record the resistance reading which is the resistance of the two coils.
Step 5. Determine if the readings you recorded are within your vehicle's specifications
The ignition coil is a sensitive component of the vehicle's electrical system. If the main or second coil is slightly outside the vehicle's specifications, you will need to replace the ignition coil as it is most likely damaged or malfunctioning.
Tips
- If you don't see a spark, check the output on the voltage/ohm meter. The main coil should produce a reading between 0.7 and 1.7 ohms.
- Official ignition coils are manufactured to different specifications and tolerances in order to affect the performance of the ignition system. Always choose high quality replacement parts.
