Mag Off, EGT High

Could be that spark is a bit more retarded with one mag or maybe just not as efficient and delaying the fuel burn slightly. Both of which could have fuel still burning as it goes out the exhaust

Hi Toni,

What you describe is exactly my own recent experince - Rotary ignition switch not fully returned to the Both position, after preflight ignition checks. I saw high EGT's soon after levelling out. Engine not delivering expected power, decided to return to fields. While trying, to inflight, diagnose problem, noticed switch not fully on Both Ignition, completed switch rotation, EGTS immediately started to drop.

Hi Gents,

I’m really only thinking out loud here trying to understand how your observations occur and these thoughts are not based on experience at all, just hypothesising.

So far, in addition to Murray’s post above, 2 obscure possibilities come to mind.

1 With one ignition system switched off, incomplete burning of the air/fuel mixture is a possibility, I wonder if the function of the ignition firing on the exhaust stroke as mentioned in the MMH (attached) is igniting the unburnt air/fuel mixture in the exhaust valve port/exhaust and showing as an increased EGT.

2 This one I admit is a bit “out there” but I wonder if the plug that is not firing is a little fouled & somehow acting as a glow plug producing a detonation/post-ignition effect?

Cheers, Des

That's interesting regarding the firing at TDC of the exhaust stroke.  It makes sense that there would be some small amount of unburnt fuel with one mag off, otherwise there wouldn't be a small but noticeable increase in power/smoothness when it's turned on.  Possible, but probably not a partially fouled plug, engine only has 110 hours.

I felt kinda dumb when I realized what I did - the way things are situated I have a storage pouch on my shoulder belt that impedes my view of the mag switches so it wasn't obvious until the red light started blinking. 

Also Des, not all pilots are "gents". 😀 

Toni

🙏 Sorry Toni, my mistake 🫣