Fch

[FCH]

I have a 912ULS in my Speedster.
The ignition switch is key operated with off, left, right and start. On the last flight, on shut down, the off position would not shut down the engine. the RPM would drop to 500 then cycle back to 1000. It would continue to do this, so I had to shut off the fuel to stop the engine.
I suspect the switch is gone bad. Am I on the right tract or could something else be causing the problem

[Dave S]

FCH,

Don't get too carried away and replace the switch just yet.

The problem you describe is a classical P lead open - There are two wires running from the switch to the ignition modules - If one if these wires becomes disconnected; or, breaks, the problem you describe is exactly what will happen.

When you turn the switch to off, the switch contacts will ground each of the two P leads shutting the ignition off. The switch can be checked with a multimeter to verify it is grounding; but, your problem is likely not the switch.

Check the P leads for continuity and solid connection at the switch and at the modules. The P leads on the engine side are subject to vibration and can crack resulting in a open condition. Wires can sometimes crack internally under the insulation. A good tug on the wires will usually find that. The screws on the switch can also come loose if not tight enough.

[Av8r3400]

This is a very common failure on Rotax 912 series engines.

There has been much debate here on this, but LEAF has replace many faulty left-right-both switches due to their incompatibility with the CDI ignition. I trust their expertise.

[FCH]

Thanks for the info
This Speedster is a 1993 model and has been working fine for over 1500 hrs.. I am going to do some double checking of the wires. I had one break several years ago.

[tommg13780]

After sitting 6 months during off season I had a kill switch malfunction. I went old school fix by eliminating the stake-on connector at the module and going twist and solder/encapsulated with 2 layers of heatshrink. This is the second time for this problem on 2 different 912's and I've only accumulated around 200 hours flying time total on both.

[FCH]

In checking the P lead wires I found one break under the insulation. Repaired it and checking the other P lead I found another area that the wire had broken all but one strand. Repaired it. Haven't had a chance to fly, but I run the engine and then turned it off with the switch and it worked OK.
When I had a P lead break several years ago, when I turned off the switch the engine continued to run normally. This time when I turned off the switch the engine would cycle between 500 and 1000 RPM.
I really zip tied the wires down so I hope they won't break again.
Problem solved.

[Slyfox]

I love mine on individual throw switches. the starter is on key, will change to push button some day.