Method1
Performing an Ignition Coil Spark Test
1
Turn the vehicle off and open the hood. As with most types of vehicular maintenance, you’ll want to begin the test with the vehicle in park and with the engine off. Open the hood to locate the ignition coil. Though its precise location may vary from vehicle to vehicle, generally, it is located near the fender or bolted to a bracket fairly close to the distributor.
- One sure-fire way to find the ignition coil is to locate the distributor and follow the wire that does not connect to any spark plug.
2
Remove one spark plug wire from its plug. Next, remove one of the spark plugs’ wires from the plug itself. Usually, these wires run from the distributor cap to each of the spark plugs individually.
3
Remove the spark plug using a spark plug socket. Once you’ve removed the spark plug wire, remove the spark plug itself. This is easiest with a specialized socket wrench called a spark plug socket.
4
Attach the spark plug back to the spark plug wire. Now, carefully reattach the spark plug to its wire. You should be left with a spark plug that’s connected to the distributor but not seated in its “hole.” Handle the spark plug with insulated pliers to avoid the possibility of electric shock.
5
Touch the threaded portion of the spark plug to any exposed metal in the engine. Next, maneuver your spark plug (wire still attached) so that the threaded “head” of the plug is touching some metal part of the engine. This can be virtually any sturdy metal part of the engine block – even the engine itself.
- Again, hold the spark plug carefully with insulated pliers (and, if possible, gloves). Don’t risk electric shock in the next few steps by neglecting this simple safety measure.
6
Remove the fuel pump relay or fuse. Before you crank the engine to test the spark plug, you must disable the fuel pump. When this is done, the engine will not start, allowing you to test the coil for spark.
- Failing to remove the fuel pump relay means cylinder being tested will not fire because there is no spark plug. It will, however, still be flooded with fuel, which may cause serious damage.
- Check your manual to locate the fuel pump relay.
7
Have a friend “crank” the engine. Get a friend or assistant to turn the key in the vehicle’s ignition. This will provide power to the car’s electrical system and, thus, to the spark plug you’re holding (assuming your ignition coil is working)
8
Look for blue sparks.
- Orange sparks are a bad sign. These mean that the ignition coil is supplying insufficient electricity to the spark plug (this can be for any number of reasons, including cracked coil casings, “weak” current, faulty connections, etc.).
9
Carefully re-install the spark plug and re-connect its wire. When you’ve concluded your test, ensure the vehicle is turned off before essentially repeating the preparatory steps above in reverse order. Disconnect the spark plug from its wire, re-insert it into its hole, and re-connect the wire.
- Congratulations! You’ve completed your ignition coil test!
Method2
Performing an Ignition Coil Resistance Test (“Bench Test”)
1
Remove the ignition coil from the vehicle. The test above isn’t the only way to determine whether the ignition coil in your vehicle is functioning as it should.
2
Find the resistance specifications for your ignition coil. Every vehicle’s ignition coil has its own unique specifications in terms of the electrical resistance within the coil. If your coil’s actual resistance levels fall outside of these specifications, you’ll know that your coil is damaged. Usually, you’ll be able to find the resistance specifications unique to your vehicle by consulting your service manual.
3
Position the leads of the ohmmeter on the poles of the primary coil. The distributor will have three electrical contacts – two on either side and one in the middle.Turn on your ohmmeter and touch one lead to each of the outer electrical contacts. Record the resistance reading – this is the resistance of the coil’s primary winding.
4
Position the leads of the ohmmeter on the poles of the secondary coil. Next, keep one lead on one of the outer contacts and touch the other to the central, inner contact of the ignition coil (where the main wire to the distributor connects). Record the resistance reading – this is the resistance of the coil’s secondary winding.
5
Determine whether the readings you recorded fall within your vehicle’s specifications. Ignition coils are delicate components of a vehicle’s electrical system.
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