CDI Trouble?

[Wheels]

I was sitting on the runway doing a mag check in my 80 horse Rotax912.
I flipped the right mag switch to off and the engine died for about 2 seconds then restarted. Then died, then restarted. This pulsing death indicated that maybe I should not fly. So I'm down.

I didn't see anything in the CDI wiring that looked amiss so I pulled the toggle switch and had it tested. It was showing some resistance, so I bought a new one. I reinstalled the switch, same problem. I reversed the switches just to make sure, its still the right mag that fails.

Any ideas? I thought I would just send the module to a rotax facility and have it tested but, should I look for anything else first?

[kitfox2009]

I would very carefully recheck the ground wires coming from the bottom of the modules. They can break internally with little indication on the outside.
Good luck
Don

[DesertFox4]

Wheels- Don has a good point.
That is also a semi-common problem on the ignition modules especially if the modules are still mounted on the engine side of the motor mount. I remounted mine to the firewall side of the engine mount for less vibration. I fought this problem until discovering the broken ground wire.

The ground wires can flex right near where they come out of each ignition module. If the copper strands break inside the wire insulation you can get intermediate grounding problems or a complete module drop out but the wire looks normal. The module is completely fine but the ground wire has no continuity or is intermittent when the engine is running and shaking.

You may have to use the sewing needle procedure and a continuity tester to hunt down the exact spot that might be causing the problem. Use the needle or needles to poke through the insulation starting at the module and using the tester you may locate after several attempts the spot where the copper strands are broken. After each needle poke, attach to tester to the needles and wiggle the wire to see if the tester shows continuity. If you find the bad spot hopefully it is far enough from the module to splice in a new section of wire.

[Dutch]

I had the same problem on a mag check. On mine it turned out to be . One of the leads in the stainless braided sheaths, just before the modules. The needle probe test revealed the problem, and I was able to splice in a new piece of wire. Anything that flexes and or is subject to vibration should be suspect.Dutch

[68niou1]

I have a spare CDI if you need it to test- call me or PM me.

Scott

[Wheels]

I did check the continuity from all the switches to the CDI. All checked good. I needle checked the cdi sheath and couldn't really determine conclusively what is going on. I removed the CDI and will send it to Rotech for a test. Thanks for all the suggestions, I'll let you know how it goes. As an aside, I took a lot of pics but I'm not real sure that reinstalling a cdi to the coil is going to be a cakewalk. I might need some help on that one, wires everywhere, I marked them as best I could but this may be a challenge.

In the mean time, I can clean up the plane.

[68niou1]

Jay- I don't remember changing the CDI as being very hard, you should have two plugs and a couple of wires if I remember correctly(ground, ignition switch) Are you going to be around tonight? I might be able to fly up and bring my spare- I make no promises though

[Wheels]

I"m around tonight but gone most of tomorrow. Might be fun. Call me 208 290 8558

[Planesmaker]

A broken ground wire will not stop the engine, quite the opposite you will not be able to stop the engine. I would check the red wire coming into the CDI it is common for them to break internally. Tom

[jrevens]

A broken ground wire will not stop the engine, quite the opposite you will not be able to stop the engine. I would check the red wire coming into the CDI it is common for them to break internally. Tom

If the ground wire in question is part of the power supply to the CDI, it'll stop the engine... right?