Ignition Failure of a Yamaha 115R Outboard Motor CDI

Ignition failure in the Yamaha 115R outboard motor may sometimes be tied to the engine's capacitor discharge ignition system, or CDI. The CDI isn't the only potential cause of problems like spark plugs firing intermittently or ignition module failure. These are symptoms, and can stem from other problems withing the engine. Good troubleshooting is the key that helps you sort out the true cause of the problem.

  1. Intermittent Firing

    • You can use a good inductive tachometer to compare the spark plug firing in the cylinders from idle up to wide open throttle. An inductive tachometer measures the number of rpm in a motor by counting the number of electrical pulses occurring within the coil or within a cylinder, usually the "No. 1" or topmost cylinder on an outboard. If the inductive tachometer is moved to the different cylinders of an engine that has a cylinder that's firing intermittently, it will appear as if that cylinder is producing fewer rpm. If there's a difference between one cylinder and the others, it can be caused by a stator coil, a charge coil or even an ignition coil that shorts to the ground at certain temperatures or under certain load conditions. It can also result from an internal failure in the CDI.

    Cylinders Misfiring

    • Yamaha outboards produced after 2001 normally use either one ignition module or one CDI per cylinder. When you see cylinders misfire, first check the trigger coil for that cylinder. If an engine has multiple CDIs, you can move them from one cylinder to another to see if the problem follows them. If the problem remains with the original cylinder, a part or system other than the CDI is the root cause.

    Blown Ignition Modules

    • When the engine blows out its ignition modules continually, particularly if the problem limits itself to the same cylinders over and over, you need to replace the ignition coils. A bad coil will set up an inductive kickback loop that destroys the modules. The coil may test good with every test you can imagine, so the only test that works for coils isn't a test -- it's replacement. If you replace the coil and the problem continues, it may be the stator, since a stator that tests good can send spike voltages to the modules, causing them to fail.

    Troubleshooting

    • When you troubleshoot a problem with the CDI of the Yamaha 115R outboard, it's much like troubleshooting any problem -- start with the system, then test the components in a logical order to narrow the problem down to a single subsystem or part. When testing the CDI to determine if it is related to an ignition failure, the problem must be present during the test. If this means that an intermittent problem only shows up at a certain temperature or under a certain load, bad components may pass the tests.

      This means you either must test the problem while it's happening naturally, or you must cause the problem by duplicating the operating conditions under which it occurs, even if it means you have to go boating.