The ignition coil, a vital component of any vehicle's ignition system, is responsible for providing electricity to the spark plugs. When a vehicle will not start, misses often or stalls frequently, its ignition coil may need replacement. Luckily, a relatively quick, simple test can determine whether the ignition coil is functioning properly and thus whether a trip to the auto parts store or mechanic's garage is warranted. See Step 1 below to get started!

Method 1 of 2: Performing an Ignition Coil Spark Test

1. 
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   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 starter or under the distributor cap. Note that in vehicles without a distributor, the spark plugs will be connected directly to the coil.
   • 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.
   • Before beginning, it's very wise to ensure you're wearing safety goggles or other eye protection and that you have access to insulated tools (especially pliers) to protect from electric shock.
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2. 
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   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. To prevent injury, be very careful when working with your vehicle's electrical system - use gloves and insulated tools at all times.
   • If your vehicle has been running for a while, its internal components are likely to be very hot. If so, give your chance a vehicle to cool down for 5-10 minutes before taking this initial step.
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   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.
   • From this point forward, be careful not to let anything drop into the empty hole left where your spark plug was. Leaving debris in this hole can cause damage to the engine as the vehicle runs and, since removing anything from this hole can be a big pain, it's best to take preventative care to ensure nothing of the sort happens.
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   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.
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   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.
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   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)
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   Look for blue sparks. If your ignition coil is working properly, when your friend cranks the engine, you should see a bright blue spark jump across the spark plug gap. This spark will be clearly visible in the daylight. If you don't see a blue spark, your ignition coil is probably malfunctioning and needs replacement.
   • 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.).
   • The final possibility you may observe is that no spark occurs. This is usually a sign that either the ignition coil is completely "dead", that one or more electrical connections are faulty, or that you've done something wrong in your test.
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   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!