Most ignition coils have three wires, some have four. Two of the terminals provide power and ground. The third could be a trigger signal wire. Finally, there might be a fourth wire to tell the engine management system when the coil fired.
Service information will typically include information on how to test the coil inputs. Avoid back probing the connector. You could inadvertently ground or short a circuit and damage an ECM or ignition control module.
One test to avoid performing is removing a coil or plug wire to see if a spark is present. First of all, this is an invalid test that can give you inconclusive results. Second, the spark you are seeing is not a sign of a healthy ignition system. The spark you are witnessing is at 14.6 psi and not the 130 psi or more inside the cylinder during the top of the power stroke. Third, the uncontrolled spark could damage other electrical components like the coil next door. Do not remove the coil’s connector while the engine is running to see if a misfire or rough running condition changes. Audi and other European OEMs advises the connector should never be removed if the key is in the on position.
One of the best ways to test the condition and output of a coil is by using a capacitive probe to measure the secondary ignition waveform. If you can’t find a “known good” waveform, compare the waveform to another coil on the engine. To test the primary side of the coil, you can use a current probe placed around the positive wire going to the coil. With this test, you can see if the power is being sent to the coil and if the engine management system is controlling the coil by the current ramp.
Now you have confirmed a coil is damaged or non-functional, it is time to replace the coil. Remember, when replacing an ignition coil, always use a high-quality coil such as this Blue Streak U575 or late-model Audi and VW applications. Blue Streak import coils are reliable because they’re a product of superior design, manufacturing, and extensive testing.
Make sure the ignition is off. Look at the service information to confirm what parts need to be removed to access the coils and plugs. On this engine, the engine cover and these PCV lines on the valve cover need to be removed.
Always replace or at least inspect the spark plugs. The condition of the plugs and their gap could have caused the original ignition coil to fail in the first place. Use a small amount of dielectric grease on the inside of the boot. The grease will make installation easier and help to seal the boot to the plug.
After everything is back together, check for codes in the engine control module. Also, you can check the misfire monitor to see if it has been completed and passed.
This video is sponsored by Standard Motor Products.