Toobuilder

Toobuilder

Well Known Member
I have a little more than a year and about 150 trouble free hours on the dual Pmags on the -8. Last weekend I changed the oil and also decided to install a whole new set of NGK plugs. The old ones looked great, but at $18 bucks for a whole set, I change them out every year. Ground run up is normal, with only the EGT rise to indicate I'm running on left or right. Test flight is normal as well, as a mag check at 100 ROP produces no discernible difference in power in the climb (again, only an EGT rise). Top of climb, and my usual 50 LOP cruise setting is completely normal. So far so good.

Where it goes off the rails is when I try a final mag check in the 50 LOP condition. Selecting the right mag only (which runs ALL the bottom plugs) causes the engine to fall on its face. It still runs, but is clearly not happy. Selection of the other mag (top plugs) all is well (slight EGT change). I found that I can richen up the mixture and the "problem child" (RH Pmag) starts to behave normally. To be thorough, I reinstalled the old plugs and was able to duplicate the condition.

So my problem is that I'm not sure I've ever done the mag check in LOP cruise before, so I don't know if this is a new issue (or ANY issue, for that matter). Since all indications are otherwise normal, and I can bring the errant ignition back into normal ops with the mixture, I suspect that the difference is tied to the combustion chamber of the Lycoming engine.

Is there anyone out there running the "all top, and all bottom" split in their ignition, and have you run across the same issue as I have?

Thanks!
 
I'm really curious about this too. Could you please not PM your response, as I would like to benefit from the discussion as well. Thank you very much.
 
...or because its just easier to hash it out on the phone...

Anyway, considering the engine would not run LOP with two "good" Bendix magnetos (if there is such a thing ;)...), I'm a long way from throwing stones at a single PMag for not picking up the slack. Lighting off a super lean mixture takes a very healthy spark, after all.
 
Which is worse, hazardous to sales or hazardous to safety? I'm not trying to be cute with this question...just sincerely interested in making my system as reliable as possible by learning about everyone's experiences. Thank you.
 
Dual P Mags

Let's see, Fifty degrees Lean Of Peak, shut off 1/2 my ignition, induce roughness. What a surprise.

Why don't you try that again and enrich the mixture, then report back.

Mike Bauer
N918MB RV6 O-360 Dual Pmags
 
I have not had the discussion yet, but I'm not ready to think this is a safety issue at all. After all, single ignition while LOP is hardly normal ops.

...But if you do mag checks like this, AND run PMags split top\bottom, please speak up.
 
MontanaMike said:
Let's see, Fifty degrees Lean Of Peak, shut off 1/2 my ignition, induce roughness. What a surprise.

Why don't you try that again and enrich the mixture, then report back.

Mike Bauer
N918MB RV6 O-360 Dual Pmags
Click to expand...

Please read post #1 again...

My question is not THAT it gets rough... (Expected). It is why one ignition takes the load as a single, while the other does not. My theory is that it has to do with the proximity of one plug to the intake port compared to the other. I'm looking for others to share their experience so that I can rule out my ignitions.
 
P-Mag

Mike I have a carb and cannot get much LOP with BOTH ignitions, at least on all cylinders.:)

Can we assume you are GAMI / Fuel Injection? If you are carb, maybe a mag check in that situation is not telling you that much about your ignition, more about your fuel flow. That was my point.
 
Timing?

I suggest you first check that both Pmags are timed correctly and are synced, if you haven't already done so. And are you certain they are both configured to the same timing curve?
Also, do you have the solid top plug or the screw on? And are you sure they are all seated correctly?
You might pull the plugs wires back off and check if the dielectric grease is blackened, if so you have some arcing going on in there, like from screw on plug terminals.
BTW mine runs fine on one PMAG down to 80-100LOP
0-360/Bendix/PMAG/slick
Tim
 
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Michael, My P-Mags are wired with one powering the top plugs and the other powering the bottom (I cannot remember which is which) it drops more RPM when testing the left (not LOP) and I have always assumed it was the flame travel or whatever because of the plug positions. At one time I thought of changing one to the top on the right and the bottom on the left and vise versa for the other mag to see if that would even it out.

Bob
 
OK, I think this is like one of those cases where you go to the doctor and complain that it hurts when I do "this" - and his answer is " then don't do that"...

My ignitions perform exactly as they should according to the manual and what 99.9% of pilots do before every flight (end of runway "mag check"). Additionally, for those that advocate doing a "real" ignition stress test (climb power check), my ignitions also pass with flying colors.

The only place where I'm having anything less than perfect combustion is a fairly extreme condition - well LOP and one set of plugs firing. Considering how much work goes into plug location for racing engines, the basic geometry is a very important factor for efficient combustion. So it is not unreasonable to expect a fairly radical difference between the two plugs which are on opposite sides of a huge combustion chamber. After all, the two plugs are not there because of safety/redundancy - two plugs is a requirement to ensure that relatively slow flame front makes it all the way across the chamber. To make matters worse, a lean mixture is a slower burn than a rich one.

Anyway, I have some more digging to do, but let's not jump on this as an ignition "problem". On that note, if anyone has a angle valve, fuel injected, dual Pmag engine (firing all top and all bottom) and would like to do a mag isolation test at 7500 feet and 50 LOP, I'd like to hear the results. I'm going to try it with my other airplane tonight, but it is a parallel valve and that may be a big difference. I'll let you know.
 
Michael and I spoke on the phone this morning. The purpose of the call was to talk over what is going and why he is seeing the results he is.

Let me reiterate what he is doing and experiencing.

At altitude, while running 50* lean of peak, he decided to perform a mag check. This is something most of would never try. Heck, I don't know very many pilots who shut off one ignition, in flight, on a perfectly smooth running engine but Mike did.

His setup is also slightly non-standard in that he has the right P-mag firing all four top plugs and the left P-mag fires all four bottom plugs.

This is on an "angle valve" 200 HP IO-360 engine running NGK auto plugs.

Here are a few facts / thoughts about this setup, that others may have missed and Mike and I discussed.

1. It is difficult to light off a lean mixture.
2. As Mike mentioned, when running lean, the flame propagation is very slow. That alone can make the engine run rough.
3. The "angle valve" engine is actually a hemi-head. So yes, he has a Hemi it. This means that the standard reach auto plugs are slightly recessed, when compared to the parallel valve engines. That, coupled with the location of the bottom plugs with relation to the swirl of the fuel/air mixture may make it difficult to light the charge.
4. Since these are auto plugs, the ground electrode (The little tang that bends over the center electrode) could be blocking / shielding the spark from the minimal fuel charge.

Other things we discussed were the possibility of a loose connector or a plug wire touching the engine mount. Both of those can cause a misfire, as I have found out while debugging issues uncovered by customers running our EICommander.

Mike is going to do some more testing and will report back to this thread, once he knows more.

As a reminder, this issue came up while performing an unusual test in extreme conditions and is not necessarily indicative of a problem with the P-mags. Neither Mike nor I have anything to hide and only hope to gain more operational knowledge of these P-mag, which we will share, once we understand what is going on.

As a side note, my partner in the EICommander developed a test rig, similar to an accessory case, that allows us to spin two P-mags in a controlled environment while adjusting the RPM, manifold pressure, timing, etc. We have tested P-mags in various flight configurations without leaving the ground and risking our lives or my engine.

In all the testing we have performed at various RPMs and manifold pressures, we have been unable to trip-up the P-mags in normal operation.
 
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MontanaMike said:
Mike I have a carb and cannot get much LOP with BOTH ignitions, at least on all cylinders.:)...
Click to expand...

BTW, I have an ECi O-360 in my -9 and can run it as much as 100* LOP before it starts to get rough. However, I typically run it 50* LOP.
 
N941WR said:
Michael and I spoke on the phone this morning. The purpose of the call was to talk over what is going and why he is seeing the results he is.

Let me reiterate what he is doing and experiencing.

At altitude, while running 50* lean of peak, he decided to perform a mag check. This is something most of would never try. Heck, I don't know very many pilots who shut off one ignition, in flight, on a perfectly smooth running engine but Mike did.

His setup is also slightly non-standard in that he has the right P-mag firing all four top plugs and the left P-mag fires all four bottom plugs.

This is on an "angle valve" 200 HP IO-360 engine running NGK auto plugs.

Here are a few facts / thoughts about this setup, that others may have missed and Mike and I discussed.

1. It is difficult to light off a lean mixture.
2. As Mike mentioned, when running lean, the flame propagation is very slow. That alone can make the engine run rough.
3. The "angle valve" engine is actually a hemi-head. So yes, he has a Hemi it. This means that the standard reach auto plugs are slight recessed, when compared to the parallel valve engines. That, coupled with the location of the bottom plugs with relation to the swirl of the fuel/air mixture may make it difficult to light the charge.
4. Since these are auto plugs, the ground electrode (The little tang that bends over the center electrode) could be blocking / shielding the spark from the minimal fuel charge.

Other things we discussed ware the possibility of a lose connector or a plug wire touching the engine mount. Both of those can cause a misfire, as I have found out while debugging issues uncovered by customers running our EICommander.

Mike is going to do some more testing and will report back to this thread, once he knows more.

As a reminder, this issue came up while performing an unusual test in extreme conditions and is not necessarily indicative of a problem with the P-mags. Neither Mike nor I have anything to hide and only hope to gain more operational knowledge of these P-mag, which we will share, once we understand what is going on.

As a side note, my partner in the EICommander developed a test rig, similar to an accessory case, that allows us to spin two P-mags in a controlled environment while adjusting the manifold pressure, timing, etc. We have tested P-mags in various flight configurations without leaving the ground and risking our lives or my engine.

In all the testing we have performed at various RPMs and manifold pressures, we have been unable to trip-up the P-mags in normal operation.
Click to expand...

You might have something there with the plugs being recessed and covered buy the ?electrode, also maybe that he is firing only bottom plugs on one P-mag. Can he get longer plugs? In theory it would be better off if it was running well on both plugs.

As one more data point I have slick mags firing Unison fine wire plugs on a 200HP angle valve IO-360 A1A at 20 degree advance, I am one who does do regular mag checks in flight and wile LOP, both my mags pass nicely and the same even at 50 LOP.
 
Russ McCutcheon said:
... Can he get longer plugs? In theory it would be better off if it was running well on both plugs.
...
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This question has come up in the past and I just don't know what plug would work. Today I sent an email one engine builder to see if they have a dead angle valve cylinder they can send me. If so, I will try a number of different plugs in it and report back.

If anyone reading this has useless cylinder they want to give up for the cause, please contact me.
 
Russ McCutcheon said:
...As one more data point I have slick mags firing Unison fine wire plugs on a 200HP angle valve IO-360 A1A at 20 degree advance, I am one who does do regular mag checks in flight and wile LOP, both my mags pass nicely and the same even at 50 LOP.
Click to expand...

Thanks for that data point Russ. I'm guessing that you have the conventional crossover harness, so if my angle valve theory was correct, you would have two cylinders go cold on one mag, then the other two on the other mag... I flew the Hiperbipe today and tried to repeat my experience, and while I did see a difference between top and bottom plugs, it was not nearly as dramatic as the last flight with the -8.

So I went back to basics on the problem child and may have a smoking gun... The "weak" left PMag was found to have the coil connector screws loose and the connector body not seated. The ship side connector screws were also loose but the body was at least seated. I'm guessing that this was something I overlooked last year when I put it back together after the major rewire. I'll try fly it tomorrow and see if that's it. I'm hopeful, as the symptoms fit an intermittent connection.

Stand by.
 
Toobuilder said:
Thanks for that data point Russ. I'm guessing that you have the conventional crossover harness, so if my angle valve theory was correct, you would have two cylinders go cold on one mag, then the other two on the other mag... I flew the Hiperbipe today and tried to repeat my experience, and while I did see a difference between top and bottom plugs, it was not nearly as dramatic as the last flight with the -8.

So I went back to basics on the problem child and may have a smoking gun... The "weak" left PMag was found to have the coil connector screws loose and the connector body not seated. The ship side connector screws were also loose but the body was at least seated. I'm guessing that this was something I overlooked last year when I put it back together after the major rewire. I'll try fly it tomorrow and see if that's it. I'm hopeful, as the symptoms fit an intermittent connection.

Stand by.
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Yes I have the standard harness, one mag fires the top on one side and the bottom on the other side. I definitely don?t have two cylinders dropping out during a mag test LOP in flight, that would get your attention for sure!

Seems like some others have reported having problems with those screws coming loose on the P-mag connectors, seems like someone reported there solution for this.
 
Flight test tonight showed no change. Ignition looks great and performs perfectly in all normal respects, so until someone else with an angle valve and an ignition firing all top and all bottom plugs can tell me it runs smooth on either set of plugs, I'm at a loss. I'll keep looking, but it's kind of a back burner deal for the time being. If I get really motivated, I may just swap the ignitions side to side and see if the behavior follows the ignition or the plugs.
 
Michael

Can you confirm the cruising altitude and power setting you have when doing a 50dF LOP mag check.

I suspect I have the answer, but even then not entirely sure it will be correct.

Lets assume you are at 7500', WOT/RPM2200-2500/and 10dF LOP, do the test that way. See what the result is.

at maybe 1500-2000' WOT, a 50dF LOP mag check would work also.

Happy to discuss offline by skype until you get a resolution that you can bring back to the boards.
 
Ahhh I see ;)

OK go out and try the same test at 7500, WOT 2350, and use 10dF LOP

Might be interesting to see.

By the way, using 50LOP at that power setting is not efficient, your speed loss Vs fuel flow is too great. 10-20 LOP is going to be better.

Cheers! :)
 
I can try that, but I suspect that it with it that rich (10 LOP), it will be fine. In prior tests with the single ignition "misbehaving", I can slowly richen the mixture up and the engine fires normally again. The odd part is that it does not come back slowly, as most engines do when you go too lean- it is all at once, like a light switch. The behavior is very "electrical" in nature. That's why I thought the loose connector was the cause.

To your other point, the 50LOP setting was not arbitrary. That is the sweet spot for this engine/airframe. The speed drops off rapidly leaner than that, but the difference between 10 LOP and 50 is only about 4 knots at a cost of 1GPH. That is a relatively expensive four knots.
 
Update

Ok, so my Hiperbipe has dual PMags set up all top and all bottom but it is not an angle valve. It does not exhibit the same behavior that the RV does, but acts "normal" on one ignition or the other in all respects ( no roughness, just an EGT rise). It acts the same whether on the ground, at climb power, or at 9000 feet/50 LOP...

So today I pulled the suspect ignition out of the RV and replaced it with a borrowed one from the Hiperbipe. Long story short, the engine runs fine now. The behavior followed the one ignition unit to the bench. Looking at it, I see that the over temp sticker on the body is now dark - so it saw at least 200 at one time or another.

I have not talked to Brad yet, so we should probably keep the speculation down to a dull roar, but I will certainly let you know the outcome of any repair action.

Just as a recap, this is a 113 series with all the updates, about 100 hours TTSN, with the only hint of a problem at altitude and 50LOP.
 
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200 Hp Angle-valve info

OK, MIke, I went out and did the test for you.

I have an IO-360-A1A angle-valve 200 Hp. Bendix FI.
Light Speed Plasma II EI fires Denso spark plugs on top
Slick Mag, timed at 24 BTDC, fires all the bottom, standard aircraft plugs.

7500 ft, 2400 rpm, WOT, leaned 50-60F LOP (Fuel flow about 8.3 gph)

On the Light Speed only (top plugs), ran a little rough, EGT's rose a littel

On the Slick mag only (bottom plugs) it ran pretty darn rough, but not like it was going to quit, or shake the airplane apart. There was a significant loss of power, but with the C/S prop, it kept turning 2400. EGT's rose quite a bit.

I was wondering if it would misfire badly enough that the EGT's might drop, but nope, the EGT's went up.

Sounds like you already figured out you had a borderline P-Mag? but anyway, I don't think there is anything special about the bottom plugs relative to the top plugs. I think my rougher running is from a weaker spark with less spark advance on the Slick mag.
 
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.
 
If this turns out to be the case (weak coil), that does present an interesting situation for the PMag equipped.
Click to expand...

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. :)



01-14-modis02.gif
 
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 said:
Would an EI Commander have shown anything odd going on?
Click to expand...

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.
 
ColoRv said:
Would an EI Commander have shown anything odd going on?
Click to expand...

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.
 
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.
 
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.
 
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