PMAG Problem

[gbusterguy]

I recently had a problem with my PMAG. Some facts; I have a RV7, Superior IO 360, One Mag and one PMAG serial No. 1775, installed over 2 years ago, I have a standard Bob Knuckles electrical system design, and a B&C alternator.

We were flying at 7,500?, Good Wx, smooth air, lean of peak. Suddenly the engine began running very rough simultaneously the alternator light illuminated. I immediately richened the mixture which didn?t change the roughness. We began to notice an electrical burning smell, not a good sensation. I activated the emergency bus, turn off the master switch and punched in nearest airports in the 430 GPS. The smell dissipated.

We then noticed that the cylinder head temps were in the red. Was this for real or part of an electrical issue? I checked the oil temp., it was above normal. We reduced the power to 42% which was enough to maintain our altitude. The cylinder head temps returned to the green. The engine roughness continued. We considered a mag check but thought it best to leave out that option for fear of making things worse. We pressed on to KUKL, home base at a 130 kt ground speed.

Once on the ground I did a mag check, the engine ran fine on the mag but would not run on the Pmag. We found the connector on the end of the power wire coming off of the alternator had broken after 10 years of vibration and had been arching between the wire and the alternator, thus the elec. burning smell. We found the Pmag timing was out. I was able to retime it following the Emag instructions.

What happened? A clue was found on the Emag website under ?Tips and Tricks.? It says to be sure that your Pmag is off when you charge your battery because the pulsing or cycling of some battery chargers can scramble the timing of the Pmag. It seems that perhaps an electrical pulsing in flight can have same effect on the timing.

Fortunately this happened in good Wx at a relatively high altitude, I have a 4 cylinder EMS and I was flying with another pilot who was a huge help in sorting thing out, and I only had one Pmag.

The Pmag has been sent back to the manufacturer for evaluation. My engine has been inspected for damage by a very competent aircraft mechanic. It has been determined that the rings got hot enough to lose their temper; one cylinder has some scrapes on the cylinder wall. I am replacing that cylinder, rings and all 4 pistons as a precaution. I haven?t given up on EI but I am going to put my mag back on until all this timing business gets resolved.

[Bevan]

You did a great job of getting things sorted out. Switching to one mag, then the other would have identified the problem mag.

The Pmag should be operating exclusively on internal power at that RPM unless is was the older Emag version (non-self powered).

What version of Pmag?

Bevan

[Canadian_JOY]

Unless that P-Mag has the latest firmware, it will still be susceptible to losing its timing if powered up and down while the engine is running. Version 40 firmware is a "must have" for P-Mags. Some P-Mag owners think they don't need the newest firmware because their cockpit switching technique removes the possibility of them inadvertently power-cycling the P-Mag with the engine running. Unfortunately that line of thinking doesn't cover some of life's other little eventualities, like stuff that happens beyond our control, and the control of our ignition switches.

[flyboy1963]

....okay, it's refreshing to know when 2 of the smartest guys I know BOTH pitch in and post when there's a problem!
....and I don't even have a P-mag........yet!

[WAM120RV]

Hi

I have read this with interest as I have two Pmags, and can I congratulate you on your diagnostic work on working out what caused the problem with your P Mag. I will certainly make sure I check the connections on my alternator to make sure this does not happen to my system.

Also good decision making in your actions to ensure a safe flight and return to the ground. I had a very similar experience with a Lightspeed EI. It popped the circuit breaker for no apparent reason. CHT and EGT rose. It would not reset so I carried out very similar actions to you, got the temps down and landed.

I checked all my wiring and found no fault and after resetting things on the ground it all worked again, however several hours later the EI developed a misfire which I could not cure, hence my change to dual P mags.

I wonder why though you have titled this as P Mag problem. What you had was a problem with your alternator connections which apparently caused a timing shift on your P Mag. The Pmag was apparently happily doing its job and would have continued to do so had the alternator connection not failed?


It's great to know that the failure mode of PMags with certain chargers can be replicated by an arcing alternator connection and Emagair should in my opinion include this information in their manual so that the connection gets checked. I have now added it to my list of repetitive checks in my engine log book, so again thanks for that.

I am though perplexed as to why you seem to be identifying the PMag as the culprit when it was in fact the victim of a wiring fault. I guess if it gets the brains at Emagair to come up with a solution to prevent this failure mode then that will be great, but all us P mag owners can do to prevent a similar failure is to ensure the integrity of our charging system.

Thanks again for posting this, it really is good information to have and could save a life. Actually come to think of it I am glad you posted it as PMag problem or I might not have read it. Well done try to ensure Emagair include this failure mode in their manual!

[WAM120RV]

Originally Posted by Canadian_JOY

Unless that P-Mag has the latest firmware, it will still be susceptible to losing its timing if powered up and down while the engine is running. Version 40 firmware is a "must have" for P-Mags. Some P-Mag owners think they don't need the newest firmware because their cockpit switching technique removes the possibility of them inadvertently power-cycling the P-Mag with the engine running. Unfortunately that line of thinking doesn't cover some of life's other little eventualities, like stuff that happens beyond our control, and the control of our ignition switches.

Does this mean that V40 pmags would not suffer this type of failure mode?

[Whitman]

Just a quick reminder to check emag website for service notes. I just had an emergency in flight and would have benefited greatly from seeing this before hand, reference case bolts on pmag in my case. More to follow once I get the plane flying again.


http://www.emagair.com/service-notes/

[N941WR]

Originally Posted by Canadian_JOY

Unless that P-Mag has the latest firmware, it will still be susceptible to losing its timing if powered up and down while the engine is running. Version 40 firmware is a "must have" for P-Mags. Some P-Mag owners think they don't need the newest firmware because their cockpit switching technique removes the possibility of them inadvertently power-cycling the P-Mag with the engine running. Unfortunately that line of thinking doesn't cover some of life's other little eventualities, like stuff that happens beyond our control, and the control of our ignition switches.

I can't stress enough how important the Version 40 upgrade is, if you have a mixed ignition environment and/or use toggle switches to ground your P-mags.

Originally Posted by WAM120RV

Does this mean that V40 pmags would not suffer this type of failure mode?

Yes, that is what this means.

It turns out that pre-version 40, when the P-mags are powered (or spinning above 800 RPM) and they are grounded, they are in setup mode. Which means two puffs in the manifold line will change their TDC mark to wherever the crankshaft is when the P-mags get the puffs.

With the shorting described by the OP, the system was being grounded, which puts it in setup mode. (Powered but grounded is setup mode.)

When your intake valve closes there is a short duration but high velocity positive pulse in your manifold pressure line, just like the puff it takes to set the timing.

Version 40 is different in that the prop must be stationary to set the timing. Thus a spinning P-mag will not allow its timing to be changed.

So to answer the question, this problem was solved in late 2014, so depending on the vintage of your P-mags, you want to get them in for the update.

Here is the link to the Emag Service Notices. While they don't list it as "mandatory", our experience is that it is required. Think of it like a certified airplane's Service Bulletin vs. AD.

gbusterguy, check your PM's.

[Mark Dickens]

Originally Posted by N941WR

It turns out that pre-version 40, when the P-mags are powered (or spinning above 800 RPM) and they are grounded, they are in setup mode. Which means two puffs in the manifold line will change their TDC mark to wherever the crankshaft is when the P-mags get the puffs..

So, if I understand this right, when you do your run up, and individually ground out the PMags to test the RPM drop, this inadvertently puts the PMag in setup mode as long as the P Lead is grounded out? This seems to be quite different from what Emagair put on their website...please clarify.

[N941WR]

Originally Posted by Mark Dickens

So, if I understand this right, when you do your run up, and individually ground out the PMags to test the RPM drop, this inadvertently puts the PMag in setup mode as long as the P Lead is grounded out? This seems to be quite different from what Emagair put on their website...please clarify.

There is a difference, and I'm not sure how to address it properly.

What we found is that in startup mode (below 200 RPM), it is very possible to reset the timing, IF one P-mag is in setup mode and the engine cranks over.

Now, to answer your question, once the engine comes out of "startup" mode (above 200 rpm), it should not be possible to reset the timing. However, with the OP's situation where there is some shorting event going on, all bets are off.

If a mag check were able to reset the timing, there would be many more lost timing issues than we have heard about.

The lost timing event that V40 addressed typically happens with ignitions of different types or two P-mags operated by toggle switches and a P-mag is left grounded for starting. When this happens, we found there is about a 40% chance of resetting the TDC mark.

Timing with Version 40 is slightly different, you have to set the prop to TDC and then power up the P-mags. If the prop turns after the P-mags are powered up, you cannot reset the timing, regardless of the RPM.

The other change that V40 has is to fire the plugs at 4 degrees AFTER TDC for starting. Pre V40, they fired the plugs at TDC. Thus you do not have to "clock" the P-mags, if you have a lightweight prop.

I hope all that is clear.