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:D

[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?

[Planesmaker]

Of course, I was referring to the ground wire to swithes that turn ignition off, sorry if ambiguous. Tom

[Wheels]

I installed another CDI yesterday and the result was a total failure at the right mag check. The replacement CDI is suspect as it had been removed after a similar problem to mine, but I will switch the cannon plugs this morning and see if the problem moves to the other side, if so, great! I"ll order a new CDI, if it doesn't, boohoo as the adventure unfolds.

[trentp]

I had this same issue recently, we found that one of the wires going from the ignition switch to the module was worn down and was grounding out. We pulled the wire away from the metal clamp it was in and it has been perfect ever since.

[Wheels]

Just got a call from the test facility. The module failed. I have a new one on order. They must be very proud of the little fella cause it cost me 900 + dollars. I hope the other one is ok. Do they usually die in pairs?

[68niou1]

I'm not a smart guy- but I don't understand how you only had failure on one side and both modules are bad? Does not make any sense to me. Also I don't believe it is common to have both modules fail at the same time- that's why I had a spare:D

[Dusty]

Ignition modules
one thing that appears to happen is the modules fail to provide ignition for startup( having run perfectly the day before ,and usually not at a convenient location)
We suspect that one fails first but isn't detected as the engine starts ok and a mag test doesn't show anything wrong as the speed is well above normal cranking speed
When the other follows you're stuck(what appears to be two dead modules)
In aircraft with dual kill switches we will sometimes start on left or right mag only ( this wont work with combo switches) so far we havn't got a definitive answer but think we may be on to something,
Just hope this may help

[Wheels]

Found the problem. A broken wire (red wire) on the harness at the bullet connector. spliced a new section in and replaced the connector. No abnormal ops.
I used the pin method to find the break but it took a long time. because the break was at the connector and it wasn't a complete break. the couple of strands of wire that were still connected gave the indication of continuity but the "limpness" of the wire end indicated the break. I eventually broke the wire inside the rubber sheath while searching that area. Wow. What a lucky break. ha ha.
Test flight went well yesterday. Just made a lap. Today is a heavy weather day, so I am washing, waxing, and polishing.

[Dave S]

Wheels,

"What a lucky break" love the humor!:D

Got a question. There have been many comments on the relative merits or lack thereof on soldered vs crimped connectors. Hard to beat actual experience as opposed to theory. Was the offending break on a soldered or crimped connection? Also, can you comment on the length of service of the particular connector (years/hours).

Always looking for info which will help increase reliability of our craft.:)

Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

St Paul, MN

[Slyfox]

my opinion. with all my years working on cars and such. if you know how to solder. nothing else can beat it.

[Wheels]

Dave the calendar age of the plane engine install is 1999. Actual flight time is 590 hours. always hangared. Engine removed twice for maintenance on water empellor and oil seal replacement, then once for engine mount crack. These maintenance ops resulted in obvious disconnection and re connection of the harness and probably didn't help anything. the crimp was aircraft quality and I used the same method for the repair. I will have the boys at the local Avionics repair shop check my work and redo any suspected weakness.
I wrapped the entire bullet connection bundle in silicone self galvenizing tape. Then zip tied it for security. It aint movin.

[Dave S]

Wheels,

Thanks for the follow-up info. I hadn't considered the potential effects of intervening maintenance - good point....I think your securement of the repaired connection will insure reliability. You know, when I discovered the silicon tape......that's great stuff...then I wondered where it had been all my life! I find myself adapting many of the tricks I learned on building & maintaining our plane to my automotive work (including use of the silicon tape) .....my wife even has aircraft grade hardware on her Swedish Weaving Loom now.

Slyfox....your comment about knowing how to solder correctly is golden....when I have seen failures on soldered wiring, almost always seems to be due to technique issues or securement

Sounds like Wheels is good to go!:)

Fly well,

Dave S

[Planesmaker]

Thanks for letting us know. Interested, was the ign unit really failed?
I had the red wire fail at about 100hrs, broke from vibration, it was a rotax crimped connection.
About ignition unit double failure, I have seen it several times (on several aircraft) , it is the slow speed start circuit that fails, once at speed normal circuit cuts in operates normally. Seems it is only later model units with 2 plug connectors. Earlier units that have seperate bullet connectors for grounding wires and the red wires don't seem to suffer from this failure. Expensive units, you can get away with buying only one unit to start the engine. I have found a place in Western Australia that can repair for half the cost. I believe it's a thrimister that fails( probably a 50c part). Tom

[Wheels]

I have not tested the other two units I have been playing with. one was my old unit, I need to test it. the other is a friends unit and I need to test it as well. both units were suspected failures and simply replaced. Quite possible that neither is bad. I"ll let you know, but to be honest with you, I'm tired of maintenance problems with this motor. I flew for a few minutes last night after the repair and although the plane seemed fine, I was not having any fun. Tonight, same feeling, this does not bode well my friends. I"ll take some time and evaluate the components I have shelved and let you know the results, but I may need some time to evaluate my situation and make proper decisions. Don't hold your breath, but I'll get to it.

[Slyfox]

If it were me I would change out the red wire on both. plus bypass the connector, solder all the way baby with heat shrink. if you have your cdi's mounted on the motor, get that moved as well to the motor mount, less vibration. make sure your grounds are connected to a separate mounting direct to the battery ground. eliminate the possibility of vibration breaks and forget about it.

[Wheels]

I've put about 50 hours on the new CDI. Plane runs like a sewing machine. Its a beautiful thing. I'm happy again.

[Slyfox]

are you going to the fly-in?

[Wheels]

yes, I'm taking my bride and doing some route planning now. It's harder than usual but I have reservations at the holiday inn.:D

[AirFox]

Good to hear your feeling better about the plane. See you and Pam in McCall.

[68niou1]

I am glad your plane is running better. It's frustrating when you have problems- but when everything is right they sure are fun!!!😃👍