Non Problem? (Pmag Question)

[Toobuilder]

Thanks Steve. Some others have run the same test (with PMags) and showed essentially the same performance on either ignition. So that all backs up my latest flight with a good ignition installed. Talked with Brad and he suspects a weak coil pack. I'll do some more parts swapping in the coming days and see if I can confirm the theory. I have to admit, it makes sense.

If this turns out to be the case (weak coil), that does present an interesting situation for the PMag equipped. This is a condition that apparently ONLY shows up when the ignition is highly stressed (LOP). Now, I don't know how long I've been flying on this "weak" ignition because the other one was carrying the load, but if my remaining ignition had "failed" while I was fat and happy in cruise, it sure would have raised an eyebrow!

I don't know about the rest of you, but the "LOP stress test" is going to be a part of every flight from now on.

[Ted Johns]

If this turns out to be the case (weak coil), that does present an interesting situation for the PMag equipped.

This type of failure (damaged coil - weak output) can happen to any ignition system. It's one of the more difficult issues to diagnose, unless you have an ignition scope. A Snap-on MODIS is a good choice.

[Toobuilder]

Well, I reinstalled the original "suspect" ignition but swapped coils with a known good ignition. Flight test shows all is well again. So it came down to a weak coil after all. No visible damage, swelling, leaking, bad terminals, etc. looks brand new, and with 100 hours on it, it should. So with info in hand, I called Brad and he immediately sent me a replacement coil. I'll send him the bad unit in the hopes he can figure out the failure.

Which brings us to the "interesting" problem: I don't know when this coil went bad, or if it ever worked correctly for that matter... It could have been bad from the vendor that Emagair uses. So I would encourage anyone running one of these should do a "meaningfull" stress test. If you don't have the diagnostic equipment Ted mentions above, it might be a good idea to do the LOP, cruise mag check. I certainly will from now on. It appears the standard run up does not tell you much.

One more data point: these ignititions on my airplane are only on their second set of plugs, and those were swapped out just recently. The last 100 hours has seen a great deal of long cross country time, LOP. So when I pulled the plugs, they looked like they were burning great - good color, no lead fouling, etc. However, upon closer inspection, the bottom plugs showed significant erosion of the ground. NOT in the gap between the electrode and the ground, but on the piston side. It looked pitted and eroded, like a rat had been chewing on it. Initial thought was detonation, but the piston looks great, there is no evidence of aluminum on the plug, and the top plug looks brand new. Anyway, I don't care to speculate as I've never seen plugs do this, but there seems to be some kind of correlation. After all, the commonality was the "weak" ignition and the eroded plugs. Did one condition cause the other? Chicken vs. egg...

Anyway, I'll keep a close eye on the plugs and report back if things start to go sideways.

[ColoRv]

Would an EI Commander have shown anything odd going on?

[N941WR]

Originally Posted by ColoRv

Would an EI Commander have shown anything odd going on?

Good question. The answer is probably. We haven't run into a client with this issue but since the EICommander measures the dwell on the spark discharge below ~2200 RPM, it might catch it. Above that number the P-mags are busy firing the plugs and stop reporting coil data.

[John Collier]

I remembered these columns...this one regarding the LOP Mag check...they are good reads...

http://www.avweb.com/news/pelican/182179-1.html

-JC

[Brantel]

Originally Posted by ColoRv

Would an EI Commander have shown anything odd going on?

During my time messing with creating a display for the data that comes out of the P-mag, I found the data on the ignition coil discard rate unreliable. I assume the EI Commander uses this data for its display but that is only an assumption.

[Toobuilder]

Well, my discussions with Brad gave me the impression that this "weak coil" situation is a pretty rare event. And in all likelihood it is, after all, ignition coils are not exactly rocket science to manufacture.

However, considering that this bad coil passes the normal run up checkout with flying colors might mean there are a few more floating around. We won't know how many more until people start doing a LOP check or some other kind of diagnostic tool becomes available. Of course, I guess this is no worse than magnetos - they certainly loose their fire over time and no one panics about that. The magnetos that were in this airplane passed the mag check on the ground too, yet even with BOTH firing could not keep the engine lit much past peak EGT, let alone 50 LOP.

[Toobuilder]

Quick update to this saga:

From the first "coil failure" event, things continued to malfunction at random intervals, but very quickly after each "fix". Ultimately, I had 3 different units fail in this airplane within an hour of installation. All of these units gave flawless performance up to that point, and all were sent home to emagair and checked out with no defect noted on the bench. One of my boards was replaced with a 114 unit as a "hail Mary"... I rewired the power side, ohmed the spark plug leads and plugs, checked grounds, etc. all to no positive effect. The final act was to change out the new non resistor plugs with the old, 100+ hour resistor plugs. This change put it back into the original "pre problem" configuration and seems to have done the trick. I've been running a new set of resistor plugs now for a few tanks of gas and the ignition is rock solid, just like the 150 hours prior to the change to non resistor plugs.

So my preliminary conclusion is that the PMag does not like non resistor plugs. I'm going to run a few more tanks of fuel through the engine, and then switch back to the same non resistor plugs and try induce a failure. If that happens, then I think we can close the book for sure on this one.

In the mean time, I'd caution against installing NON resistor plugs in your PMag equipped engine.