It is uncommon for a CDI module to have an internal failure, but not impossible - they are an electronic component.
Two things will contribute to CDI failure, HEAT and VIBRATION.
The installation manual states that the CDI module must NOT be subjected to temperatures greater than 80 degrees Celsius.
The internal electronics can be damaged by continuous heat soaking of greater temperatures.
Watch the internal cowl temperatures on tightly cowled installations. Some installations have exhaust systems that are routed above the engine, radiating high tempraturees directly on the modules.
Vibrations from poorly maintained engines can cause damage to the wiring over time.
Wire breaks can be difficult to locate and difficult to repair.
Ensure your engine is running as smooth as possible by keeping the RPM's up at idle, maintaing the gearbox, balancing the carbs etc.
The ignition systems on Rotax aircraft engines are dual redundant systems.
Having a complete, simultaneous, dual ignition system failure is extremely unlikely.
Daily pre flight checks and mag drop checks (as required in the Operators Manual) will let you know of any problems in each ignition system.
What are the symptoms of the failure, as most times it is due to the wires breaking down internally, usually on older engines. The wire appears to be ok until you pull it.
Mark
IMG_1372_2012-06-25.JPG (You do not have access to download this file.)
Thanx michael for your reply:
i think the engine is mounted as per installation manual, and no such extreme vibrations are observed. one thing you pointed out is temp, that can be the reason but in my case only CDI A is failed, one thing i would share is my engine is 912ULS, and its run time is abt 100 hrs.cdi failure was detected in ignition check which was done because of rough starting.
Hi,
as rhere was rough starting so during ignition check it was observed that during ignition check of CDI A RPM does,nt drop. by replacing the A it get started smoothely,
In despite of those saying that CDI failure is a very rarely issue, I can tell you that it is a very common problem. At the tremendous high price they are selling CDIs, I'm sure rotax is doing a good money selling those buggy modules. Oh, and if one of your CDI modules failed, be prepared, the another one won't last much.
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