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Ignition Coils

How to judge whether coil need to be replaced or not?


Ignition coil troubleshooting begins by disconnecting a spark plug wire and installing an extra spark plug into the end of the wire. Lay the spark plug on a part of the engine where the plug will be resting against a good ground. Turn the engine over by having a helper hold the key in the start position while the spark plug is observed for a good spark.
It is not a good idea to hold the plug wire during this procedure because electricity always takes the path of least resistance to ground and that may well by you. The coil generates from 17,000 volts upward. The good thing is that the coil does not generate much amperage so the shock would most likely be no more than an electrifying experience. Some coils are a capacitor discharge system and have enough amperage to be potentially harmful. If you are not familiar with which type is present, it is wise to keep hands at least 4 inches away from the wires when the engine is operating.
A good, blue spark should be seen jumping the gap of the plug. If you see a very weak orange spark or none at all, the primary coil wire or the coil is suspect. Shut the engine off.

Check the coil wire for continuity with a volt-ohmmeter by disconnecting it and attaching one lead to either end of the coil wire and watching the resistance displaced on the ohmmeter. If the coil wire shows excessive resistance, which would be over 3,000 ohms, replace it.
Disconnect the positive and negative wires on the coil. Use the ohmmeter to check the continuity between the positive terminal and the negative terminal. There should be a little resistance in the form of .001- .007 ohms. Now move one of the leads to the center coil tower. Use the other lead to test both terminals to the coil tower. The resistance should be between 7,500 to 18,000 ohms. If the coil has failed either of these tests, replace the coil.

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