Routing EGT/CHT wires with p-leads

I installed a MGL 3 1/4 inch TC-3 and it seems to be okay but when I turn one mag off at a time the CHT readings go bananas. I'm thinking it might be because I ran the probe leads through the same hole in the fire wall as the mag p-leads.

The p-leads are mil spec shielded wire grounded at the mag end etc...

Before I drill new holes in the firewall I'd be interested to hear others experience.

Ensure your p lead shield ground is terminated at the magneto and not under the panel somewhere. Also make sure your EIS is grounded behind the panel. I had to install some resistors at key switch per GRT to prevent possible EIS short from grounding out mags. There also were some settings on EIS that filter out the 300V spikes from the mags.

Egt/cht wiring should not be less than 1 1/2" from alternator cable, battery cables or p leads. They are very sensitive. The ss braid is for chafe/heat protection and not shielding.

I ran all of mine over to right side and back to GRT EIS 6000 along with all other low current/voltage sensor wiring. Hope some of this helps.

For what it's worth, I have always bundled my shielded p-leads with the CHT and EGT wires together. They exit the same hole in the firewall, and I have never had a problem, either with a GRT EIS or Dynon.

Even when you switch one of the mags off?

Ant CB said:

Even when you switch one of the mags off?

Click to expand...

If the question was posed to me, the answer is no. No changes when I switch off a mag.