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Pmag Issue - Diagnosis Help

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Kyle Boatright

Well Known Member
I'm finishing up my condition inspection and ran into an issue with the pMag. It was working fine before the inspection, so there's a good chance that the problem is/was related to the maintenance/inspection.

In any case, the symptoms are roughness and lumpy idle on the pMag below about 1300 rpm. That occurs with the pMag alone or the pMag+Mag. At 1300 RPM and below, the engine runs better on the mag alone than on both ignitions.

Above 1300 rpm, the engine runs fine.

These symptoms began a week or so ago when I awakened the engine after the condition inspection. As part of the inspection, I had pulled the pMag to check for shaft play and normal rotation. No problems were identified. To remove the pMag for the inspection, I disconnected the 6 pin connector that attaches to the pMag, and subsequently reconnected it. I've checked/tightened it since then, with no improvement.

In talking with Brad at Emagair, he had me troubleshoot the system by looking for problems in the power and grounding wires. No problems were identified. Tomorrow, I'm going to run a direct circuit from an independent battery to power the pMag to rule out (or in) a power/ground problem.

Any other suggestions?
 
Tell us more:
- Clean/replace plugs?
- Reset timing on the pMag and/or Mag?
- Check plug wire resistance and connections on both ends?

Carl
 
Tell us more:
- Clean/replace plugs?
- Reset timing on the pMag and/or Mag?
- Check plug wire resistance and connections on both ends?

Carl

New plugs on the pMag. Cleaned/gapped the mag plugs. All 8 plugs appear normal and the issue does not appear to be on the mag side.

The mag timing was still correct (25*btdc), so I did not change it.

Yes, I reset the pMag's timing (back to 0* btdc). It is necessary to reset the timing when you remove the unit to check the shaft play (or lack thereof). I've reset the timing 3 different times. It is possible I'm doing it wrong, but if I am, I'm doing it with the manual in my hand, and after getting it right 8 years in a row. ;-)

Initial problem was with an 8 year old set of wires. One wire didn't pass the resistance check. A new wire set didn't cure the problem.

Still, the issue didn't occur until I pulled put everything back together after maintenance. I'm wondering if the 6 wire connector didn't hold up to another remove/reseat cycle and why things smooth out at ~1300 rpm.
 
Did you try setting the Pmag to the same value (not TDC) it was before the problem started? :confused:

TDC is where it is supposed to be set. That is where it should have been before, and I (re) set it to that value 3 different times. A re-read of the manual confirms that I did it correctly unless my confirmation bias is out of whack.

If I can put my hands on the old plugs (Ron's suggestion) I'll try that tomorrow to see if a bad plug is the culprit.
 
Jumper tight?

Take a look at the wires in the connector on the Pmag. I have the jumper installed (as do most). The only problem I had with my Pmag was due to one end of the jumper not being tight in the connector. This caused the timing to change as the loose jumper made and un-made contact. Inspect the pins in the connector to verify they are clean when you check this. Certainly a quick simple check.

Any chance one of the new plugs is bad? If you still have the old ones or another set of new ones it would be another possibility. I agree with the post above to look first at anything touched since it was fine before.
 
I have noticed that p-mags do not always install correctly. The seem to have a loose fit in the mag bore. I once installed one so that it seemed fine, but the gears were not actually meshing. I never ran it like this to see the symptoms, but I would remove and then re-install the p-mag so that you are sure it is seated properly with no force. When I did it everything looked fine, but it required tightening the studs to get it seated.
I would also check for vacuum leaks.
 
I had two issues with mine that created a similar situation to what you describe. One issue was with the connector. One of the wires, I think it was the ground wire was not tight in that green connector. I couldn?t pull it out, but I could tighten the screw holding it about a full turn. If you tin the ends of the wires, they might be able to withstand the crush they experience in that connector. I also had a connector that wasn?t seated fully in the Pmag. Again, it looked OK, but when I wiggled it, it seated in further and I was able to tighten the hold down screws a little. I didn?t actually run it in that condition, as I discovered it during re-installlation. I?m not a fan of that kind of connector on an aircraft engine.

The other issue I had was a suction leak in the manifold pressure line - again it was installation error. My initial install included a section of nylon pitot/static type line after the #3 aircraft hose, with a couple of those safe-air fittings. Those fittings work great for your pitot/static lines, but not so great in a vibrating engine environment under suction. It created some erratic engine behavior. I changed it out to standard aircraft engine hose (TS Flightlines), + aluminum hard line, then transitioning to the silicone lines supplied with the Pmag kit. Much better and it fixed the erratic behavior.
 
TDC is where it is supposed to be set. That is where it should have been before, and I (re) set it to that value 3 different times. A re-read of the manual confirms that I did it correctly unless my confirmation bias is out of whack.
Yes I know the manual says TDC but if it worked then and doesn't work now the equipment is trying to tell you something and I would listen.

FWIW my pMag install works best when set at 1* AFTER TDC.

:cool:
 
Yes I know the manual says TDC but if it worked then and doesn't work now the equipment is trying to tell you something and I would listen.

FWIW my pMag install works best when set at 1* AFTER TDC.

:cool:

Mine seem to run great at 25*btdc but curious what process did you use to determine that 1* worked for you?

We have a new 14 on the field as of yesterday and the builder (Synergy Air) has the engine idling at 1050 and it runs rough as heck, I think somebody adjusted the idle because they didn't properly time the PMAGs to the IO390, haven't done any investigation yet, just the first thing that came to mind.

(sorry for the thread drift but something may come that helps)
 
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Take a look at the wires in the connector on the Pmag. I have the jumper installed (as do most). The only problem I had with my Pmag was due to one end of the jumper not being tight in the connector. This caused the timing to change as the loose jumper made and un-made contact. Inspect the pins in the connector to verify they are clean when you check this. Certainly a quick simple check.

...

The P-mags only check for the jumper at start-up. Once they are spinning, you could remove the jumper and it wouldn't matter.

Over the long weekend I helped two different local pilots with P-mag issues. One had a broken plug wire clip at the sparkplug. Push on all the connectors, both at the cool pack and at the sparkplug. If it moves at all, investigate further.

The other was really odd in that sometimes the P-mag would work fine and another time in the same flight it wouldn't work at all.

Both pilots are sending their P-mags back for inspection and repair just to be safe.
 
Mine seem to run great at 25btdc but curious what process did you use to determine that 1* worked for you?

We have a new 14 on the field as of yesterday and the builder (Synergy Air) has the engine idling at 1050 and it runs rough as heck, I think somebody adjusted the idle because they didn't properly time the PMAGs to the IO390, haven't done any investigation yet, just the first thing that came to mind.

(sorry for the thread drift but something may come that helps)
After talking with Brad at eMags and some trial and error i settled on the 1*ATDC. I guess if you have an EI commander finding the "sweet spot" would be easier but don't know. At about 1* ATDC my engine runs smoothest while the CHT's stay within a very acceptable range.

To avoid confusion; the Pmags don't get set to 25*BTDC they get set to TDC and the internal program adjusts the spark to fire at 25*BTDC, but I guess you already knew that. In my case, since I set mine to 1* ATDC, they are actually firing at 24*BTDC.

:cool:
 
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Kyle, are you at KVPC trouble shooting this?, if so give me a call and I will help or at least provide a second set of eyes ( with glasses). Text is fine.
 
Not timed correctly

One of your magnetos isn't correctly timed or someone dropped a spark-plug. Oh, wait electronic mag? Forget it. I only know about the stuff that's worked for the past 100 years.

I don't know what you mean by pMag, that must be experimental lingo for the magneto with the impulse coupling? If your engine starts, the impulse coupling did it's job. What releases or disconnects the impulse coupling are "flyweights" that when spun, disengage the retarding of the mag. I would look at everything else before the impulse coupling.
 
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It is unlikely that this is caused by your 6 pin wire plugs since once the PMAG is running, its dependency on the power/GND goes away unless below 800-900 RPM, and if it was dependent on that, it would probably just not produce any spark and engine would die.
I know you have checked the sparkplug and its gap, but perhaps if you get one new sets of spark plug and try them. If it was not, it will not be waste of money as you will use them on your next annual. Same thought with your Spark plug wires.
Lastly, maybe checking the timing by pulling the plugs and connecting them to the spark plug wires and grounded and as you turn the prop, check for the spark at each spark plug to make sure they fire correctly and all four will fire. If you do that, make sure your slick mag is off or perhaps not connected at all to make sure the engine will not accidently fire up as you are turning the prop.

Hope this helps.
 
One of your magnetos isn't correctly timed or someone dropped a spark-plug. Oh, wait electronic mag? Forget it. I only know about the stuff that's worked for the past 100 years.

I don't know what you mean by pMag, that must be experimental lingo for the magneto with the impulse coupling? If your engine starts, the impulse coupling did it's job. What releases or disconnects the impulse coupling are "flyweights" that when spun, disengage the retarding of the mag. I would look at everything else before the impulse coupling.

P-Mag is made by E-Magair, an electronic ignition. No impulse coupler involved. Most people replace the impulse coupled mag due to its higher likely hood of failure.
 
One of your magnetos isn't correctly timed or someone dropped a spark-plug. Oh, wait electronic mag? Forget it. I only know about the stuff that's worked for the past 100 years.

I don't know what you mean by pMag, that must be experimental lingo for the magneto with the impulse coupling? If your engine starts, the impulse coupling did it's job. What releases or disconnects the impulse coupling are "flyweights" that when spun, disengage the retarding of the mag. I would look at everything else before the impulse coupling.

You mean those archaic tractor ignitions that are prone to failure at any time, without warning?
 
It is unlikely that this is caused by your 6 pin wire plugs since once the PMAG is running, its dependency on the power/GND goes away unless below 800-900 RPM, and if it was dependent on that, it would probably just not produce any spark and engine would die.
I know you have checked the sparkplug and its gap, but perhaps if you get one new sets of spark plug and try them. If it was not, it will not be waste of money as you will use them on your next annual. Same thought with your Spark plug wires.
Lastly, maybe checking the timing by pulling the plugs and connecting them to the spark plug wires and grounded and as you turn the prop, check for the spark at each spark plug to make sure they fire correctly and all four will fire. If you do that, make sure your slick mag is off or perhaps not connected at all to make sure the engine will not accidently fire up as you are turning the prop.

Hope this helps.
The following assumes you have your P-mags timed to TDC.

If you attempt this, the P-mags will fire at 4.2 degrees after TDC when below 400 RPM's. It does this to assist in starting. Call it an electronic impulse coupler, if you will.

Please be sure to remove at least one plug from each cylinder so the engine won't "kick" and hurt you or anyone standing close by.

I personally doubt this is the issue, but you never know.

Kyle, check your PM's.
 
Recently I had a rough running engine and noticed that this is only true when the Pmags were on ships power. Switching off the external power supply to the "rough" Pmag the engine was then running smooth. Brad assumed the circuit board is faulty and he was right. This is the most expensive repair to the Pmag so it would be wise to first follow all the previously mentioned advices.
 
Ancient history, fixed many years ago.

Carl

So, you are saying that Pmags have never failed in the recent past? I see plenty of posts to the contrary. I understand that the autonomous TDC reset feature has been removed, but still see plenty of folks reporting failures with Pmaigs. I wasn't intending to knock the product, only making the point to Bill that those in glass houses...
 
So, you are saying that Pmags have never failed in the recent past? I see plenty of posts to the contrary. I understand that the autonomous TDC reset feature has been removed, but still see plenty of folks reporting failures with Pmaigs. I wasn't intending to knock the product, only making the point to Bill that those in glass houses...

No one is saying they can't fail, same as a Slick mag or any other ignition.

We were pointing out that many of the issues reported were with early version of the ignitions software and hardware. While I don't have the numbers, based on the number of questions asked on this forum, the frequency of failures has decreased as the number of P-mags in service has increased.

The odd thing is, very few people report magneto failures. I suspect that we as a community have just learned to accept magneto failures as "normal". However, the P-mags are still new enough technology with unique failure modes, that just like a plane crash, it makes the "news".
 
You mean those archaic tractor ignitions that are prone to failure at any time, without warning?

Bill, you have become the prime defender of the PMag system...no thread critical of the PMag appears without a defensive post from you. Fair enough...you have commercial interest in a product that analyses the PMag’s performance so you have pecuniary interest in supporting the PMag. But in defending the PMag you really need to stop your silly attacks on the reliability of magnetos that are totally unsupported by any relevant statistics. On the other hand if you have relative data on the reliability of magnetos then produce it.
 
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Why Bill defends Pmags

Bill gets free stuff from Emagair,
just saying.

That's total BS, Bill has over 12K posts helping folks with Pmags and created a unique product to support that effort, what do you have to offer?
 
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Why Bill defends Pmags
Bill gets free stuff from Emagair,
just saying.

I don't know if Bill gets "Free Stuff" or not BUT.....Regardless......Sometimes "Free Stuff" is justified! Bill does an awful lot of testing and builder assistance for Emag.
 
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Hey Kyle, did you ever figure out what happened?

Not yet. Hopefully this weekend. Other life events have pulled me away from the airport for the last week or so.

As to the comments in other posts regarding Bill Repucci, Bill reached out to me about this problem and was very generous with his time on the phone offering troubleshooting advice. My sense is that he's a guy who has put a good amount of time into understanding/testing pMags and wants to help others who are flying them. I could be wrong, but I don't think he's getting wealthy riding the coattails of Emagair. In fact, I've done exhaustive studies and have determined that the only companies getting wealthy off of experimental aircraft builders are FedEx, UPS, and the USPS. ;-)
 
I have never charged Bill for the abuse either.



[ed. Gang,

Let's please keep it civil (rule #7). *Not picking on you in particular 868RM, just sticking my text here near the end of the thread (Ross' post after this was submitted before I hit submit and locked it). I needed a reply to put this in....

Bill's a good guy who has helped a LOT of people and I'm appreciative of that. I've asked him to become an advertiser in the cheap seats if he wishes to market/support his product here (rule #1) - a conversation we've been having on and off for 3+ years. Hopefully he will. I'd like to help him sell some (VAF is my full time job.........not a side project........and I'm trying my hardest to make it work).

Please play nice and follow the house rules so I can hopefully stay in business during a time when doing so isn't exactly a given.

Thanky,
dr]
 
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It seems strange that someone directly from Pmag doesn't frequent this site given how many units RV guys have purchased over the years. Arguably, the RV market launched their product line. They are a listed advertiser here. [ed. I'm working on that. v/r,dr]

Garmin, Dynon, Van's, EarthX, Vertical Power, the engine suppliers etc. all have factory reps answering questions about their products.

I think folks really appreciate getting info direct from the source.
 
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