P-MAG with EI commander weird advance problem on startup

Hi All,

I've been running a dual P-MAG setup for a few years on my Lycoming O-360 and it has developed a peculiar problem lately. Normally when I start the engine both ignitions show the advance of 19.6 at 1000 RPM (I have an EI Commander installed). However since a few months ago sometimes the left ignition goes to 26.6 after startup. I can hear that in the engine noise, EI commander shows a timing divergence warning, plus I can confirm that the timing is different by turning off one ignition at a time, so I'm pretty sure this is not an indication problem. When this happens I shut down the engine, reboot the ignitions and restart and the problem goes away. Nothing ever happens in flight or at any time after the startup. Everything else works as intended.

My ignition setup is as follows:
SW rev: 36
RPM max : 3072
ADV max: 29.4
ADV shf: -5.6
STR dly: 0

I think this started happening after my panel upgrade, but I haven't changed the schematic of how EI commander is hooked up, just replaced some wiring.

I asked Brad at E-MAG Air but he had never seen this before.

Any ideas? Thanks.

This is probably a problem with one of the pmags. I guess Brad suggested swapping them to see what happens. Might also check in with Bill Repucci to see if he's seen this. As another data point, I have mine set up like this:

RPM max:2816
ADV max: 33.6
ADV shf: -1.4

Side topic - I'd really love to get logging of the pmag data into my efis. I only glance at my ei commander from time to time, and the information there is very interesting. It would be great to look at it in the wider context of map, rpm, egt, cht, and ff.

rv8ch said:

Side topic - I'd really love to get logging of the pmag data into my efis. I only glance at my ei commander from time to time, and the information there is very interesting. It would be great to look at it in the wider context of map, rpm, egt, cht, and ff.

Click to expand...

Hi Mickey,

I installed one of these...

https://www.enginebridge.com/product/eiwifi/

In addition to controlling/programming E/PMags, it generates analog voltages for a bunch of PMag parameters like advance angle, coil dwell, temperature, etc for input to EFIS general-purpose inputs. I have advance angle and coil pack dwells going into my G3x Touch and they're written to the log file that's generated for every flight. It also has wifi and once connected you can log into it via a browser.

You've already got an EI Commander so it may not be worth your trouble to swap. But the option is there if you want access to more information.

HTH

Dave

Carefully check your wiring for an intermittent connection - can do weird things. The electrical connectors on the PMAG are made with convenient but not environment-friendly plugs. The wire has to go through the adel supplied with the mag to ensure that it isn't vibrating relative to the plug. They also get pretty hot and if they are the ones I think they are then they have a max rated temp of 105C. The under-cowling temp variations can stress/flex the screw terminations on these blocks. The spec for tightening the screw is 0.25 N-M or 2.2 in-lb, so the screw doesn't have to be mega tight; but the wire has to be very secure and should take a good tug. Startup is the time of max vibration (and shutdown too).

I assume you used Tefzel stranded wire for your wiring change? Solid wire tends to break in vibrating environments.