EIS High Altitude Misfire?

[Marc_B]

Recently was talking to fellow turbo Mooney pilots installing Surefly units and evidently there is some discussion of the possibility of a high altitude arcing/misfire in the ignition harness cap...  Supposedly there may be cases in Cirrus aircraft with an EIS installed of arcing in the cap.  I've not heard of this before and I've only found a single thread here on MS regarding this.  In speaking with Surefly, they mentioned using a high-altitude ignition harness, drilling a hole in the cap and attaching to upper deck pressure line from previous mag, or both to help prevent this.  I'm curious how frequently this is an issue and at what altitudes it has been documented?  I also couldn't find any information documenting Cirrus issues with this, but my understanding is that is where this was first mentioned/seen?  Any direct experience with this or a solution looking for a problem?

[Slick Nick]

This is why pressurized magnetos were invented. 

[Marc_B]

12 hours ago, Slick Nick said:

This is why pressurized magnetos were invented. 

Understand high altitude misfire with magnetos...But inside the magneto is different environment than at the cap.  I don't think the recommendation was for pressurizing the EIS, but rather the harness cap alone.

[EricJ]

15 minutes ago, Marc_B said:

Understand high altitude misfire with magnetos...But inside the magneto is different environment than at the cap.  I don't think the recommendation was for pressurizing the EIS, but rather the harness cap alone.

Unless there's a hermetic seal between the cap and the rest of the EIS, pressurizing the cap will pressurize the rest of it, too.   That said, the cap where the distributor is is the only place that pressurizing should matter on an EIS.    Depending on how any vacuum advance works that could be affected as well, though.