Help - Stranded after mag failure (?) in Myrtle Beach

[DXB]

Some stress today when climbing out from KCRE at Myrtle Beach, which of course does not have a maintenance shop.  Savvy Breakdown Assistance is helping (this is a nice benefit of Global Insurance BTW), and I'm flying home commercial.  

Here's the scenario: I am climbing out through ~2500ft and notice sudden roughness and see fluctuating RPM  (I initially think the governor is croaking).  I level off and reduce power to 2300 squared, but the roughness is no better, and rpm does not stabilize. I see EGTs rising rapidly and fluctuating on all 4 cylinders. Running rich or lean seems to make no difference. I return immediately for a precautionary landing, and it runs smooth after reducing power to descend. 

Here's the Savvy Analysis trace:

https://apps.savvyaviation.com/flights/3608725/8c7f423a-f1f2-41d7-8687-54a3fc328354

EGTs on all 4 cylinders are affected, so its seems like it's a mag.  So after landing and looking at this, I did a ground runup at 1700rpm with it leaned, and the right side runs smooth, the left side is almost dead but not quite (?) - it's getting maybe just a little ignition but not enough to prevent a backfire upon going back to "Both."  I also got no ignition when trying to start until I stopped cranking -again pointing at the left mag.  After shutdown, I shook the left mag with my hand, and it does not seem obviously loose.  

My question - could this be anything besides the left mag itself?  Ignition switch?  Field wire or something?  I'm not too sharp on this electrical stuff...  Ironically the mags are just past 500 hrs and I was getting ready to replace the left mag with a Surefly at annual next month .

 

 

 

[carusoam]

@DXB,

Nice analysis Dev...

Left mag seems to have gone awol...

So anything that could stop a Mag from running properly could be responsible... from its ground wire to its internal parts...

Having it run barely on one mag... might be a capacitor no longer working... there is a really good video of how mags are supposed to work around here somewhere...

You didn’t happen to collect an inflight mag test, did you?

There is a reason for doing an inflight mag test to identify a mag failing... so that way, you can turn off the failing mag...

Aparently, some failing mags can inhibit the engine operation... and it is best to have it turned off...

Congrats on making the choice to end the flight...

Can you show the last run-up you performed? That may show something interesting... like a single plug really misbehaving... or confirming that it really is just the Lmag...

Best regards,

-a-

[DXB]

13 minutes ago, carusoam said:

You didn’t happen to collect an inflight mag test, did you?

There is a reason for doing an inflight mag test to identify a mag failing... so that way, you can turn off the failing mag...

Aparently, some failing mags can inhibit the engine operation... and it is best to have it turned off...

Can you show the last run-up you performed? That may show something interesting... like a single plug really misbehaving... or confirming that it really is just the Lmag...

Yeah I thought about doing an inflight mag check but was a little rattled, and I was making decent power still so didn’t feel like messing with anything and just getting on the ground.

The runup before takeoff looks pretty unremarkable on the posted trace, except maybe weaker ignition on #1 on the right - EGT rise on L and R are otherwise very symmetric.

I did the ground runup after the flight leaned out and left was almost dead.  Should have tried it rich as well.

[carusoam]

When you get a chance, if possible... check the logs to see how many hours are on the mags...

People like to OH mags at around 500hours to avoid similar challenges...

There isn’t much external to the mag, that I can think of to look for...

PP thoughts only, not a mechanic...

Best regards,

-a-

[DXB]

7 minutes ago, carusoam said:

When you get a chance, if possible... check the logs to see how many hours are on the mags...

People like to OH mags at around 500hours to avoid similar challenges...

There isn’t much external to the mag, that I can think of to look for...

PP thoughts only, not a mechanic...

Best regards,

-a-

The mags just past 500hrs, and I was actually about to replace the left with a Surefly and IRAN the right one at annual at your home field next month.  Sure would have been cheaper if it had held out a couple more weeks 

[carusoam]

2 minutes ago, DXB said:

The mags just past 500hrs, and I was actually about to replace the left with a Surefly and IRAN the right one at annual at your home field next month.  Sure would have been cheaper if it had held out a couple more weeks 

In that case... see if Kenny can spot you a mag to get you to annual... or at least get your bird home...

Best regards,

-a-

[Andy95W]

Dev- do you have Bendix magnetos or Slick?  The Surefly uses a Slick harness, so if you do it's a fairly quick swap, especially on an M20C with the battery inside the cowling.

My suggestion is to see if you can get the airport manager to have a local owner call you.  Folks there have to have someone to do maintenance.  It's just a matter of getting the information.

Good luck, keep us posted!

[DXB]

25 minutes ago, Andy95W said:

Dev- do you have Bendix magnetos or Slick?  The Surefly uses a Slick harness, so if you do it's a fairly quick swap, especially on an M20C with the battery inside the cowling.

My suggestion is to see if you can get the airport manager to have a local owner call you.  Folks there have to have someone to do maintenance.  It's just a matter of getting the information.

Good luck, keep us posted!

Thanks- that crossed my mind as well - unfortunately the Sureflys are on backorder - mine is supposed to ship on the 12th. I’d have to get lucky with a mechanic around here having one on hand.  Also I have a bendix so need to swap to the Slick harness for a Surefly.

[chriscalandro]

That fuel pressure looks pretty concerning to me.  I'm not 100% convinced on mag.

[chriscalandro]

Also, I'm willing to bet on when you killed your boost pump.

[DXB]

18 minutes ago, chriscalandro said:

That fuel pressure looks pretty concerning to me.  I'm not 100% convinced on mag.

Pressure drops to 1.8psi (0.5 is red line for this carb'd engine) when boost pump turned off at WOT in climb - that's normal -happens most every flight.  Note fuel flow hardly budges when that happens.  So it's definitely spark and not fuel.  All 4 EGTs are effected.  Left mag check afterwards is abnormal on ground - it essentially dies. I can't be sure it's the mag itself, but it's definitely the left ignition system and affects all 4 cylinders.

[chriscalandro]

Sorry, I missed the further troubleshooting bits. 
 

still, I have the same airplane (mine is a 67) and mine keeps solid pressure. Others will chime in but I don’t think that is normal. 

[DXB]

44 minutes ago, chriscalandro said:

Sorry, I missed the further troubleshooting bits. 
 still, I have the same airplane (mine is a 67) and mine keeps solid pressure. Others will chime in but I don’t think that is normal. 

I had the FP issue looked at ad nauseam when I first got the plane 700 hours ago and discussed extensively on here (multiple prior threads).  The reading occasionally goes much lower than the 1.8 psi shown here - even below the 0.5psi redline occasionally, but fuel flow never drops (all that really matters). Other folks with carb'd birds have described the same phenomenon. My working conclusion was that there is vapor lock from time to time in the fuel line that goes to the pressure transducer, preventing an accurate pressure reading. 

Regardless, it's definitely not the problem here. 

Addendum: Here's one old thread - not sure it's the best one. 

 

[AlexLev]

3 hours ago, DXB said:

I had the FP issue looked at ad nauseam when I first got the plane 700 hours ago and discussed extensively on here (multiple prior threads).  The reading occasionally goes much lower than the 1.8 psi shown here - even below the 0.5psi redline occasionally, but fuel flow never drops (all that really matters). Other folks with carb'd birds have described the same phenomenon. My working conclusion was that there is vapor lock from time to time in the fuel line that goes to the pressure transducer, preventing an accurate pressure reading. 

Regardless, it's definitely not the problem here. 

Addendum: Here's one old thread - not sure it's the best one. 

 

I have the same fuel pressure on climbout in my M20G, so you're not alone. I dealt with a mag failure a few years back and also made a precautionary landing not at my home field. Was down for a few weeks, but the field did have a shop that took decent care of it. About 5 hours for a mag R&R + the part, which for an exchange came in at about $1,000+.

[N201MKTurbo]

Probably needs the points reset. After 500 hours they can wear and stop opening. Just takes a few minuets to do.

Well after you take it off. Sometimes you can manage with them on the engine.

[DXB]

1 hour ago, N201MKTurbo said:

Probably needs the points reset. After 500 hours they can wear and stop opening. Just takes a few minuets to do.

Well after you take it off. Sometimes you can manage with them on the engine.

Then would the retard breaker points stop functioning at the exact same moment as the main ones (i.e. after landing it wouldn’t start until key released to “both”)?   Sorry if it’s an obtuse question - my grasp of inner magneto workings is tenuous.

[Andy95W]

For whatever reason, your left magneto is grounding internally so it's not generating a spark- or if it does, its intermittent and not timed properly.

During a normal start, the left and right magneto primary points/circuits are grounded, so the only magneto circuit that is active is the retard breaker points.  Once the switch is released to Both, the primary 25° BTDC points are no longer grounded and are active.  In your situation (which is also common when an ignition switch starts to malfunction) when you release the switch to both, there is just enough rotation and energy to create just enough spark to start the engine at 25° BTDC.  In your case, since only the right magneto is functional, this is a great testament to the fact you have a very strong starter and right magneto!

Rich makes a good point- if the points were worn out, the magneto would be grounded internally.  My theory is the point hold down screw might have loosened so the points aren't opening at all.  *Edit- on second thought, that might not be the case- because if it were, the engine would start on the retard points, which yours doesn't.* In that case, something internal to the magneto is grounding it.*

It sucks that you're on hold for the Surefly until December 12.  It would be a shame that you would pull your left magneto to repair your left points just to replace it a few hours from now.  My suggestion is to cut your losses with your left magneto (which may or may not be seriously screwed) and go with the Surefly, since you're going to anyway.

[DXB]

Based on the EGT trace, it looks like the left mag gave up suddenly, but was still firing briefly every ~500 revolutions - the down spikes in EGT reduce proportionately with rpm when I went from 2700 to 2300 rpm.  That low rate of firing was enough to make it run rough and also make the governor unstable at high power. The combustion disturbance from that mag then abates when I reduced MP to descend back to the field.  In retrospect, it would have run smooth had I switched to the right mag, which would have also controlled my heart rate and blood pressure before returning to the field.  Of course it would have died when I switched to the left, then backfired when I went to right or both, unless I had the presence of mind to pull mixture out before switching again, which is not likely. That would have had decidedly the opposite effect on my heart rate, which would be interesting for engine monitors to capture in conjunction with these events .

 

[Yetti]

could be a bad ignition switch or bad P lead.   Easy things first.   Check timing.  That will rule out 2 things.  What story do the plugs on the left mag say?

Edited December 1, 2019 by Yetti

[N201MKTurbo]

After further reading, I’ve changed my mind on the problem. I’ve had a similar problem caused by the condenser wire rubbing against the magneto case. It wore through the insulation and grounded the mag. This keeps both points from firing.

If this is the case, you can easily get yourself home. If it is a Bendix mag, remove the P lead, remove the 4 screws around the point cover, pull it back and inspect the wires in there. If one is chafed through, reroute it away from the cover, put a piece of tape on the chafed wire, put it back together and if it works, fly it somewhere where you can get it fixed properly. 

[N201MKTurbo]

You may also have a bad condenser.

[carusoam]

lots o things to think about, while waiting...
 

1) If the condenser is showing some weakness or larger drain of its charge....

Does slowing the number of sparks/minute down allow the mag to run better..? (Lower rpm) (better charge in the capacitor)

2) The capacitor is one of those wear parts that gets changed out during a mag OH...(?). Their job is to store large charges of electricity... so when they fail... it can be pretty destructive to the internal construction of the capacitor itself...

3) The capacitor is typically like a large piece of aluminum foil.... collecting charge (electrons) on its surface.... to roll it up to fit inside a can, it requires a layer of insulation like a plastic film the same size as the aluminum foil...

4) If a part of the insulating layer wears/fails... the charge collector can ground on itself... changing its effective surface area....minimizing the amount of charge it can hold...

5) Sounds like the capacitor experienced a slight failure, got weaker, but still kinda worked for a while...

6) There is one oddity in the EGT graph...  each time something fails to operate.... the EGT spikes downwards...  this is not what is expected of a two mag system running on one may...

7) Running on one mag, unburned fuel goes into the exhaust system while continuing to burn...giving off its last release of energy...

8) hence the higher EGTs we see on the monitor, when clicking to the single mags...

9) along way to go... to say don’t spend too much time looking at the mag and ignoring everything else...

10) something seems to have changed on cylinder one, stronger than what is happening on the other three...

11) or what ever happened to the mag is affecting cylinder one more strongly?

12) I grabbed a close-up of the run-up of the flight Dev shared... note where I left the data mark... cyl #1 looks like it's slightly misbehaving up to this point... But really goes its own way after this point... have a look...

13) I am baffled by the periodic downward spikes in the EGT... and how Cyl#1 stands out more than the rest...

14) The second mag peak, is clearly showing that mag misbehaving... most on cylinder #1...

15) Try this PP logic... If the top plug is getting turned off going single mag... and the bottom plug is really dirty... so much unburned fuel is going to the exhaust... it is cool...  explaining the downward spike...

16) What plugs are in there? 
 

putting this all together...

17) A weak mag may not be able to generate a strong spark... a high resistance plug may be showing the affects of the weak mag first...(?)

18) great data collection Dev!, well shared...

To be Extra Clear... these are only thoughts of a PP, not a mechanic...  

Best regards,

-a-

 

 

[Alan Fox]

I could go down and switch it out if you need it

[DXB]

13 minutes ago, Alan Fox said:

I could go down and switch it out if you need it

Thanks very much Alan - Savvy Breakdown Assistance is already working with a local shop to look at it on Monday - let me see what transpires.

[carusoam]

So...

Mag check order...

Right, Left, Both...

Cyl #1 misbehaves the most on the Left Mag...(?)

We could check the drawing of mags and plugs to see which plug is turned off and which one seems to be malfunctioning....

More PP thoughts...

Best regards,

-a-