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Engine stumble and in flight mag failure on separate flights... AOG in Carlsbad.

SwimmingDragonfly96

Well Known Member
This is going to be a longer post, so anyone who reads this, I appreciate it.

I've been battling high CHTs likely due to poor baffle sealing but while I get that sorted, my A&P agreed to retard my timing to 23 on both my slick mags (engine is a lyc YO-360-A1A with about 300 hours hobbs on it). The mag retarding helped CHTs tremendously, albeit at a slight loss of power, but acceptable for me to be able to climb like I want to. The other day, after a very long taxi at the KMCC zoo of an airport trying to find the FBO, I started her back up and she wasn't purring like normal, but still running alright. I did my mag check at run up, about 150 drop on both sides, entered the runway, applied throttle smoothly as normal, and the engine stumbled around 1200-1500 RPM. It was hot outside and the engine was quite hot from the previous long taxi. KMCC has a long runway, so I decided to go for it anyways. Took off, did a 2 hour bay tour, returned, dropped off my passenger, and went back to KSQL. No issues in flight at all.

Fast forward to today, 3 days after the engine stumble, started her up for my commute from KSQL to KCRQ. Run-up uneventful, everything looked good, took off with no problems and went about my merry way. Nice tailwind, cruising 190kt and even passed 200 at one point. At some point, I glanced at my airspeed indicator and it looked like I had dropped about 10 knots without any power adjustments, I looked over at my JPI-700 and all my EGTs were suddenly about 100-150deg higher than they were before. I'm a newb, and couldn't diagnose on the fly, so I richened the mixture, got my EGTs where I wanted them, and continued my flight. My TAS didn't come back up, and my fuel flow was a full 1.5gph higher than normal. 20 minutes later, glanced down, and all my EGTs had reduced back by 100-150 degrees, I leaned the mixture, indicated airspeed came back up to where it was before, and fuel flow was where I would expect it right around 8.5 gph. After the commotion and my mind calmed down a bit, I realized one of my mags must have failed and then came back to life. The rest of the flight was uneventful.

Leading edge aviation at KCRQ is going to check out my plane and see what's up as I'll have it parked there for the next 10 days or so. Not sure how much diagnosing they'll do being that it's experimental, but if anyone else is around KCRQ and could come and help me out at some point if they don't get anywhere, I would much much appreciate it.

Thanks and sorry for long-winded post.
 
Your first problem was almost certainly fuel vapor related, with a good hot-soak you got some vapor bubbles in the system and as cool fuel replaced the hot fuel all was well again, not uncommon.

Your second problem is very likely something causing one of the mags to drop out, yes.

Your third problem is going to be the shop telling you to just start replacing parts, because as you said most places don't want to touch an experimental, and they are paying for the parts anyway.
 
Your first problem was almost certainly fuel vapor related, with a good hot-soak you got some vapor bubbles in the system and as cool fuel replaced the hot fuel all was well again, not uncommon.

Your second problem is very likely something causing one of the mags to drop out, yes.

Your third problem is going to be the shop telling you to just start replacing parts, because as you said most places don't want to touch an experimental, and they are paying for the parts anyway.

Haha ****, I hope not, but I could see that happening. Thanks for your reply, gives me some reassurance on the engine stumble.
 
If the problem has gone away, it's gonna be hard to diagnose. I'd look at connections first, which might take an hour or so. After that, do you want them to start looking at mags - that could get expensive fast.

You need to give them an initial scope and work from there, approving (or denying) next steps as appropriate. Or you could get an expensive bill and <possibly> never really know if the problem was resolved.
 
If the problem has gone away, it's gonna be hard to diagnose. I'd look at connections first, which might take an hour or so. After that, do you want them to start looking at mags - that could get expensive fast.

You need to give them an initial scope and work from there, approving (or denying) next steps as appropriate. Or you could get an expensive bill and <possibly> never really know if the problem was resolved.

I’ll see what they say. If they’re at a loss, I’m going to have them time it back to 25 and see what happens. A&P that retarded the timing thinks it’s an issue w the retiming.
 
The difference in timing from 25 to 23 should not cause what you saw unless your A&P is implying he did something wrong. You did not say if you have full engine monitoring but it sounds like one mag dropped completely off line for a bit. As others mentioned sounds like a connection issue. Could even be in the key switch area.
The first problem as others posted is almost normal for the conditions you posted. Fuel getting boiled until you upped the flow and got some cooler fuel in the lines.
 
The difference in timing from 25 to 23 should not cause what you saw unless your A&P is implying he did something wrong. You did not say if you have full engine monitoring but it sounds like one mag dropped completely off line for a bit. As others mentioned sounds like a connection issue. Could even be in the key switch area.
The first problem as others posted is almost normal for the conditions you posted. Fuel getting boiled until you upped the flow and got some cooler fuel in the lines.

He definitely implied that the mags might be out of sync. I have full engine monitoring with a JPI 700, all EGTs rose by over 100 deg. Even before the troubles during the flight I was noticing uncharacteristic EGT spreads of 120+ degrees when they usually run quite even, esp for a carb’d engine.
 
If the engine now runs normally, then fly it. If the squawk returns, do a mag check. That will tell you if it’s a mag and also which one..
 
I’ll see what they say. If they’re at a loss, I’m going to have them time it back to 25 and see what happens. A&P that retarded the timing thinks it’s an issue w the retiming.

Might do well to check the timing at 23 first and not adjust to 25. There is no reason that 23 degree BTDC timing should cause a misfire.
 
If the engine now runs normally, then fly it. If the squawk returns, do a mag check. That will tell you if it’s a mag and also which one..

I don’t have engine data in front of me, but looking at my flight log on foreflight, I have a feeling it was firing on and off a bit after that based off a totally imperfect ground speed analysis. I was also entering the LA basin so lots of variables here but I didn’t notice high EGT or fuel flow fluctuations. I did notice my indicated airspeed fluctuating however, so I have a feeling it was indeed coming in and out.

In the picture the region between the white lines was when I was having my initial issues. The later fluctuations are indicated by the fluctuating ground speed.
 

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There are a couple of mechanics at Ramona, which is 10 min away. Send me a text and I'll forward the names and numbers. I can help with transportation if necessary.

-Marc fife six 2 six four 4 fife fife 1 oh
 
There are a couple of mechanics at Ramona, which is 10 min away. Send me a text and I'll forward the names and numbers. I can help with transportation if necessary.

-Marc fife six 2 six four 4 fife fife 1 oh

A ten minute flight away.
 
Are you able to extract the data from the engine monitor and upload it to savvyaviation.com? Might get some help from those guys for a very small amount of money. Also, they can help you deal with the shop to make sure you don't get into a cycle of replacing expensive parts.
 
Are you able to extract the data from the engine monitor and upload it to savvyaviation.com? Might get some help from those guys for a very small amount of money. Also, they can help you deal with the shop to make sure you don't get into a cycle of replacing expensive parts.

I have an account with them but I don’t have my upload cable with me unfortunately.
 
There are a couple of mechanics at Ramona, which is 10 min away. Send me a text and I'll forward the names and numbers. I can help with transportation if necessary.

-Marc fife six 2 six four 4 fife fife 1 oh

Hey Marc appreciate that. I’ll see what the initial diagnosis looks like but will likely be reaching out to you.
 
How many hours on the mags since last overhaul?
You've pretty much already determined one is bad, you just don't know which one and 'data' isn't going to help you determine which one is the bad one.
Chances of a shorted P-lead wire is small.
If it was me, I'd probably recommend just pulling both and sending to a qualified mag shop for OH or ordering 2 OH'd units and send yours back for core.
 
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I’ll see what they say. If they’re at a loss, I’m going to have them time it back to 25 and see what happens. A&P that retarded the timing thinks it’s an issue w the retiming.

Your issue is not timing. When a cylinders EGT goes up 150* and power mildly falls off, that is classic one spark. If all 4 cyl had EGT go up 150*, one mag stopped working completely. That mag needs to be pulled apart by someone knowledgeable and issue addressed. If the mag hasn't been touched in 400+ hours, my first guess is egap and second would be a failing coil, though several other issues could exist. Many A&P's don't really know what is going on in the mag, so probably best to send it off to an expert. Had a buddy with a problem on our field. Not sure why, but the mech chose to take apart the mag. After the shop spent many hours and parts, the plane still wouldn't start, so in frustration, my buddy called me. Did a few things to get it to start firing and and then after breaking 5 teeth off the ring gear, I pulled the mag apart to inspect. The A&P reassembled it 180* out of phase, causing the kickbacks. Un related, but he also took it upon himself to re-wire the ignition switch. This was also done incorrectly resulting in not only a no start, but sending someone to the hospital when setting the Pmags timing due to the mag not being grounded when the switch was off. Please be careful out there. A&P is a certificate issued by the FAA after logging x hours as an apprentice and passing a written test. IT IS NOT a confirmation of a competent mechanic. Certainly not throwing stones at A&P's, just warning that like anything else in life, there are really good ones and really bad ones, with many layers in between. Many don't regularly take apart mags and you should exercise caution in letting one do so without first proving that expertise.
 
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How many hours on the mags since last overhaul?
You've pretty much already determined one is bad, you just don't know which one and 'data' isn't going to help you determine which one is the bad one.
Chances of a shorted P-lead wire is small.
If it was me, I'd probably recommend just pulling both and sending to a qualified mag shop for OH or ordering 2 OH'd units and send yours back for core.

Walt, being the technical type, do you ever just take the mag apart and see if there is something obvious? Like rotor or points closed (closing) up?


I had some mag questions and took mine apart, set and reassembled, but not very deep. They do have all the quirks of any ignition distributor. I talked to the manufacturer and they gave me a pair of breaker points:eek:.
 
What Tom said in post #8, to determine which mag is the issue.
Also, you must have a very fast plane to do 190-200 knots with 8.5G of fuel. But I suspect you might want to check your pitot/static and calibrate it to make sure your speed is accurate.
 
What Tom said in post #8, to determine which mag is the issue.
Also, you must have a very fast plane to do 190-200 knots with 8.5G of fuel. But I suspect you might want to check your pitot/static and calibrate it to make sure your speed is accurate.

Looks like it was groundspeed. That’s believable. I flew back to San Diego from CCR on Sunday and had a 20+ knot tailwind most of the way. So we are talking a TAS around 170.
 
What Tom said in post #8, to determine which mag is the issue.
Also, you must have a very fast plane to do 190-200 knots with 8.5G of fuel. But I suspect you might want to check your pitot/static and calibrate it to make sure your speed is accurate.

Groundspeed indeed, here’s a screenshot…
 

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If this does reoccur in flight, what is the safest procedure for me to turn my live mag back on?

You can test your mags in the air, in a safe altitude, and perhaps over an airport if you have reasonable concerns. A mag on its last leg will show itself much better in the air and somewhat lean. You will have get a more accurate results than the standard mag check on the ground at 1700 RPM.

If the mag check prove you have faulty mag and kills your engine, switching back to the healthy mag should get your engine running in just a couple of seconds. I have shut my engine down in the air both using mags switches and also shutting off gas and the engine came back live in what seemed to be around ONE second but I did not time it to say for sure.

In regards to your speed, do you know what was the tail wind or what was your TAS? I still think 175-180K assuming around 15-20K tail wind is rather fast for the given numbers. But if accurate, than good for you, it is nice to have a fast plane :)
 
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Walt, being the technical type, do you ever just take the mag apart and see if there is something obvious? Like rotor or points closed (closing) up?


I had some mag questions and took mine apart, set and reassembled, but not very deep. They do have all the quirks of any ignition distributor. I talked to the manufacturer and they gave me a pair of breaker points:eek:.

If I know the mags history, and I noticed the timing has changed a bit, I may take a look at the points/cam and adjust if all looks good, but... I have a excellent mag shop I send them too and prefer tp let the pro look at/OH as required.
 
How many hours on the mags since last overhaul?
You've pretty much already determined one is bad, you just don't know which one and 'data' isn't going to help you determine which one is the bad one.
Chances of a shorted P-lead wire is small.
If it was me, I'd probably recommend just pulling both and sending to a qualified mag shop for OH or ordering 2 OH'd units and send yours back for core.

The mags have 300 hobbs since new. The fact that the mags were retimed two flights ago makes me feel like it would be a fairly wild coincidence that this happened so soon after without being related. I am tempted to get the new mags, but hopefully this shop can figure something out. Thank you for your reply, Walt!
 
The mags have 300 hobbs since new. The fact that the mags were retimed two flights ago makes me feel like it would be a fairly wild coincidence that this happened so soon after without being related. I am tempted to get the new mags, but hopefully this shop can figure something out. Thank you for your reply, Walt!

It certainly could be a mag issue, and in fact that may be most likely. However, I wouldn't assume so to the exclusion of other possibilities. As mentioned above by others, a mag could be grounding out intermittently due to a switch problem, especially if you have a rotary key switch, or a damaged wire. Having just timed the mags doesn't conclusively point to them as the source of the issue. When mags were timed, it certainly would have been possible to jostle a wire that was near the breaking point such that it "went over the edge". If mag timing were part of a CI, any of the other inspection and/or repair work done at the same time could have done the same thing. I had an oil temp sender that would fluctuate between the lowest value the EFIS would display and normal, intermittently. With the cowling removed, another guy stood on the side of the plane (being VERY careful) while the engine was at idle. Jiggling the wire made the oil temp value go crazy. The insulation was intact, but the wire had broken inside. Sometimes it made good contact, other times not. A new probe and a little extra lacing cord resolved the issue.

As also mentioned by others, downloading the engine data and sending it to Savvy would be a great start in the troubleshooting process. If a mag is dropping off line intermittently, it should show up in the data. If not, the analyses may point to something else.
 
It certainly could be a mag issue, and in fact that may be most likely. However, I wouldn't assume so to the exclusion of other possibilities. As mentioned above by others, a mag could be grounding out intermittently due to a switch problem, especially if you have a rotary key switch, or a damaged wire. Having just timed the mags doesn't conclusively point to them as the source of the issue. When mags were timed, it certainly would have been possible to jostle a wire that was near the breaking point such that it "went over the edge". If mag timing were part of a CI, any of the other inspection and/or repair work done at the same time could have done the same thing. I had an oil temp sender that would fluctuate between the lowest value the EFIS would display and normal, intermittently. With the cowling removed, another guy stood on the side of the plane (being VERY careful) while the engine was at idle. Jiggling the wire made the oil temp value go crazy. The insulation was intact, but the wire had broken inside. Sometimes it made good contact, other times not. A new probe and a little extra lacing cord resolved the issue.

As also mentioned by others, downloading the engine data and sending it to Savvy would be a great start in the troubleshooting process. If a mag is dropping off line intermittently, it should show up in the data. If not, the analyses may point to something else.

Thanks for that. The joys of airplane ownership.

My wife is mailing me my cable to grab my data off the JPI. Will keep this thread updated.
 
What kind of cable do you need? if it's a standard (or variation) of a usb cable I can get one to you fairly quick.

-Marc

Hey Marc,

It's the JPI specific cable that connects to the JPI box. My wife actually overnighted it to me today, so I should have it tomorrow and hopefully have my data uploaded to savvy by the evening.

Appreciate your help, man.
 
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