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Bad pmag or engine monitor?

jell

I'm New Here
Hello. I would be very appreciative if someone could point me in the right direction for diagnosing an issue that just popped up.

I purchased an RV-6A 12 months ago and it came with dual pmags. I've flown it 50+ hours with no issue. During run up today I noticed that the RPM reading on my engine monitor was sporadically dropping to 0, every few seconds or so while on both magnetos. The engine monitor is quite old (it's an RMI umonitor) and so my initial thought was that it was failing. However, there are a few things that then made me think it's one of the pmags instead:
1. the RPM reading issue seems to only happen on the right mag or on both, not while on the left mag.
2. the engine also sounds like it's running slightly slower on the right mag (it's not running rough, just at a slightly lower power setting compared to the left mag).
3. The right mag is the older of the 2 pmags (7 years / 600 hours old). The left was replaced several years later.
4. I read in the umonitor installation guide that a failing mag could potentially cause failures with the umonitor.

So is it probable that the pmag is starting to fail? If so, what's a good way to test for that? I looked in the troubleshooting guide on the emagair website but none of those tests seem to apply to this situation.

Or are there other causes I should be considering instead? Loose wiring or something else?

Thank you very much.
 
When you do a mag check during run up, do all EGTs go up when you turn off the left pMag, go up when you turn off the right pMag?

Carl
 
I had a similar issue recently. Unlikely to be related to a failing mag, per the folks at emagair. First, make sure you are getting the RPM signal from one of the pmags. Should be just one, not both. Check the wire connection at the Pmag, I believe it’s pin 6. Pull that wire out and reinstall it, making sure no stray wire strands are hanging out. If still no change check the connection at the monitor end.
 
In addition to Carl's comment you could pull both mags, check for gear bearing play & swap the mags at reinstall to see if the issue follows the right mag.
Checking plug lead resistance may be useful too.
All that cost nothing except time :).
 
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Josh, if you have not already, I recommend downloading the pmag manual from the emagair website. These ignitions are great, but do require knowledge from the owner/operator that is different from standard mags.

I'd also recommend investing in a better engine monitor, and a way to monitor the pmags like the eicommander or the enginebridge.

There are probably 100 posts on the VAF about pmags, and you'll probably learn something from each. Both Bill Repucci of eicommander fame and Brad at Emagair are excellent sources of information. I don't know the enginebridge guy(s) but they also seem pretty sharp.
 
Hello. I would be very appreciative if someone could point me in the right direction for diagnosing an issue that just popped up.

I purchased an RV-6A 12 months ago and it came with dual pmags. I've flown it 50+ hours with no issue. During run up today I noticed that the RPM reading on my engine monitor was sporadically dropping to 0, every few seconds or so while on both magnetos. The engine monitor is quite old (it's an RMI umonitor) and so my initial thought was that it was failing. However, there are a few things that then made me think it's one of the pmags instead:
1. the RPM reading issue seems to only happen on the right mag or on both, not while on the left mag.
2. the engine also sounds like it's running slightly slower on the right mag (it's not running rough, just at a slightly lower power setting compared to the left mag).
3. The right mag is the older of the 2 pmags (7 years / 600 hours old). The left was replaced several years later.
4. I read in the umonitor installation guide that a failing mag could potentially cause failures with the umonitor.

So is it probable that the pmag is starting to fail? If so, what's a good way to test for that? I looked in the troubleshooting guide on the emagair website but none of those tests seem to apply to this situation.

Or are there other causes I should be considering instead? Loose wiring or something else?

Thank you very much.

Cooling scat tubes to the Pmags are critical. If your Pmags have overheated and the heat sensor on the side of the Pmag has turned black, your problem my be a damaged Tach circuit. The solution is to send it back to Emag and have the main board replaced. Before doing that, connect the tach wire to the newer Pmag, and only the newer Pmag. If the RPM problem is fixed, continue to fly both Pmags. The failed tach circuit will not effect the ignition function.
 
Thanks everyone for the replies. Responses below:

Cooling scat tubes to the Pmags are critical. If your Pmags have overheated and the heat sensor on the side of the Pmag has turned black, your problem my be a damaged Tach circuit. The solution is to send it back to Emag and have the main board replaced. Before doing that, connect the tach wire to the newer Pmag, and only the newer Pmag. If the RPM problem is fixed, continue to fly both Pmags. The failed tach circuit will not effect the ignition function.

Thanks Danny. I think you are at least mostly right - I swapped the wires and that solved the problem. But it doesn't look like it was overheated. I attached a picture of the sticker and it's still ash colored to my eye. Does that look right to you or was it even lighter in color initially?

Also, do you happen to know if the tach circuit is just more likely to fail than the rest of the unit? Sounds like you think this is unlikely to lead to other issues?

I'd also recommend investing in a better engine monitor, and a way to monitor the pmags like the eicommander or the enginebridge.

Definitely - a new engine monitor was already top of the list of upgrades. Will also look into your other suggestions. Thanks.

When you do a mag check during run up, do all EGTs go up when you turn off the left pMag, go up when you turn off the right pMag?

Carl

I unfortunately only trust the EGT and CHT temp probes on one of the cylinders, but it was reading as I expected (EGT went up slightly when on each mag separately vs. on both mags).
 

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Update: After switching the tach data cable from the right mag to the left mag, the problem appeared to be resolved, or at least it did during ground testing. But as soon as I got it in the air, it started again.
 
P-Mag issue 👍

I had a issue like yours and as the P-Mag had 620 hrs up I pulled it and sent it back to E-Mag for service. The mag is now running perfectly ����.

Bob
 
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Update: After switching the tach data cable from the right mag to the left mag, the problem appeared to be resolved, or at least it did during ground testing. But as soon as I got it in the air, it started again.

That greatly reduces the likelihood that the problem is in the pmag - sounds like a wiring problem, or the engine monitor you are using. Most likely a loose wire somewhere.

While you are playing around with that, it might be the right time to get one of those pmag managers mentioned earlier.
 
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