Tech Tips

Troubleshooting Faulty Ignition Coils

Written by  September 30, 2008

When your motorcycle is not running at its peak condition and you have exhausted all of the basic requirements, remember that engines require ignition systems that carry higher voltages these days, and these parts can fail. When your motorcycle has many miles and years of use, the systems have to be recognized from an ohmmeter level, not just a visual inspection.
I recently had a set of 4 cylinder coils that when the engine came up to operating temperature, the engine would lose power and stall the cylinder. When tested with the multimeter, the coils were out of specification until the coils cooled down to room temperature. If this symptom sounds familiar, I would suggest that you use the specs from your service manual or equivalent. Measuring the resistance of the primary and secondary sides of the ignition coil requires a little skill and patience and an understanding of the ignition system on your motorcycle. If you take the coils into a shop and have the coils bench tested, this is a valid test; however, there are a couple of items that can be mistakenly overlooked. This only applies to the Capacitive Discharge System, also known as CDI ignition systems. These systems have been a standard on many models of bikes from the 90’s to this very day.
Many older bikes have used the point’s style system with electronic coils, and these systems are just as susceptible to fail because of the age of the bikes that are being pulled out of sheds and garages. The same testing procedures apply to these coils, as they both have a primary and secondary wound coil, and these are very easily identified by the construction of the coil itself. The best way I can explain the coil is the wire or terminal that is located directly to the coil is the primary side of the coil and the bigger lead that attaches to the spark plug is called the secondary coil. Both of these leads have a specific resistance that is very important to the correct voltage at the spark plug to obtain the best burn for the combustion process.
Ignition coils that are intermittent must be replaced because these also are being triggered by the pickup coil or crankshaft trigger, and coils have been known to throw current back into the pickup coils and or CDI module. When you are dealing with a modern-day bike, they have really good ignition systems that are very reliable and maintenance free! Today’s new systems are really good, and when your bike has fuel injection, there are many applications for aftermarket coils and high output ignition modules that can be adjusted and set to different levels, which is very cool and functional.
So in summary, when your H-D or metric bike has an intermittent spark and the motorcycle is just not running correctly, taking a few minutes of your time to test the coil and spark plug wires is a great way to look into the ignition system and determine if you need a replacement or need look into another area in the electrical system.
B-safe out there!
By Dave Miller