Weird mag check

[The-sky-captain]

Yesterday, just before my run up, I noticed the lock nut around the ignition was very loose. I snugged it up a couple rotations and proceeded with the runup. When I switched to my left mag I heard the drop in RPM but my digital tach went from 2000 to 1993 RPM and stayed there with both "mag failed" lights illuminated. I went back to both and no change, right mag no change. Again I could feel the mag drop but the digital tach was frozen on 1993 from the first drop. Nothing I did, even pulling the prop, would make the tach unfreeze. I hit the master, it rebooted and all was fine. Has anybody out there in Mooneyspace land seen this before.

I will note that for the last month or so about 1 out of 10 starts when i would turn the key and nothing would happen. I figured it was just a bad ignition switch since the battery and Skytech are fairly new. Could the loose lock nut have cause the ignition to be too loose and short out every now and than on start up? It makes me wonder how/if the tach and ignition issue both had to do with the loose lock nut. BTW the tach is new. I had it installed at my engine OH about 4 months ago and this is the first issue I have seen out of it in the 80 hours since that I have flown behind it.

[Parker_Woodruff]

Which digital tach do you have?

[N33GG]

Hi Parker; I was getting a little work done on my Mooney today at Don Maxwell's shop and saw a pretty nice 252 sitting in the corner that looked a lot like yours.  Beautiful aircraft...congrats!

I had the same questions...which digital tach?

[Parker_Woodruff]

Quote: N6719N

Hi Parker; I was getting a little work done on my Mooney today at Don Maxwell's shop and saw a pretty nice 252 sitting in the corner that looked a lot like yours.  Beautiful aircraft...congrats!

I had the same questions...which digital tach?

[The-sky-captain]

Quote: Parker_Woodruff

Which digital tach do you have?

[N33GG]

Quote: Parker_Woodruff

Thanks!  Was the cowl on or off (checking induction leaks)?

He just finished with some fuel tank patchwork...

[The-sky-captain]

6719N- I feel the need to squawk 7500 on this thread...

[N33GG]

Understood... sorry.  I am not familiar with the detailed operation of the Horizon tach.  With other tachs, eg the EI tachs, there can be weird effects with the mag sense leads, and EI has corrective measures and procedures in the event things get a little weird (in line resistance in the leads to calm things down).  Perhaps someone with more knowledge of the Horizon unit can provide input.  Again, sorry for the off topic communication, but you should have seen Parker's 252, and you would understand!  Good luck, these kinds of problems can be very frustrating.  I hope there is a simple solution.

[Parker_Woodruff]

Quote: N6719N

Understood... sorry.  I am not familiar with the detailed operation of the Horizon tach.  With other tachs, eg the EI tachs, there can be weird effects with the mag sense leads, and EI has corrective measures and procedures in the event things get a little weird (in line resistance in the leads to calm things down).  Perhaps someone with more knowledge of the Horizon unit can provide input.  Again, sorry for the off topic communication, but you should have seen Parker's 252, and you would understand!  Good luck, these kinds of problems can be very frustrating.  I hope there is a simple solution.