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Engine momentarily dies

Earl Findlay

Active Member
For the last 25 hours, since I finished the condition inspection, about five times now, when cruising or descending, the engine stalls out for just a split second and then comes back alive. By the time one can react, it's back and purring.

I changed the spark plugs at the last condition inspection and did a compression check (78, 78, 79, 80). Oil analysis was good.

Pmag and Lightspeed ignition.

Should I change out my plugs again? Or any suggestions where to start? Prior to the RV flying it's been 25 years since I flew. I have about 50 hours on it now. Maybe this is not abnormal and I have forgot about it? Absolutely no other trouble indications.
 
NOT normal. And not enough data to diagnose from afar.
Simplistically, gas/recip engine needs 3 things to keep running: air, fuel, spark. Which one is being interrupted? Probably not air -- but that leaves a lot of detail to check out.
Intermittents are usually more difficult to cure. More specificity, like power reduction, or power change, or pitch change, or ??? change would help your mech. Might want to ride along and go find a way to reproduce it with an observer experienced in type [ABOVE THE AIRPORT]. Find your local EAA chapter, or other leads to locals experienced in model.
 
Is it a carb'd O-360 engine? If so what P/N carb do you have? Maybe one that causes that type of scenario. 10-3878 is a common carb that has been known to cause that type of issue. 10-4164 or 10-3878M are good P/N's that don't normally do it. Could be a bunch of things but 10-3878 carb definitely can cause intermittent, momentary hiccups like you describe.
Good Luck,
Mahlon
 
Occam's Razor

Something that clears that quickly makes this even stranger. A plethora of possibilities.

Apply Occam's razor and start simple. Check all of the fuel system sump and other low points; e.g. pumps, etc. in the fuel system for signs of (previously existing) water. You using 100LL or MoGas?

Please share what you find.
 
Is it a carb'd O-360 engine? If so what P/N carb do you have? Maybe one that causes that type of scenario. 10-3878 is a common carb that has been known to cause that type of issue. 10-4164 or 10-3878M are good P/N's that don't normally do it. Could be a bunch of things but 10-3878 carb definitely can cause intermittent, momentary hiccups like you describe.
Good Luck,
Mahlon

It is unlikely to be your ignitions.

Let's assume the carb is OK (But DO NOT discount Mahlon's advice!)...

If both of your ignitions dropped off line and then came back on line (This could happen if the internal generator in the P-mag died and both ignitions share a common electrical issue. Highly unlikely), you would have a backfire in the exhaust. The reason is the engine would still be pumping fuel through the cylinders and you would get raw fuel in the exhaust stacks. Then, when the ignitions came back on line, that fuel would burn off with a bang.

Since you didn't mention any backfire when it comes back on line, I would suspect fuel delivery.

Good luck and keep us posted.
 
By "stalls out" I assume you mean stops running completely for a short period of time. It is unlikely to be ignition related (both mags would have to fail at the same time) and definitely not one or a few plugs. I would be looking at fuel issues, especially given the start of symptoms after previous work.

Does it immediately stop, like switching the mags off or does it get rougher before it stalls? Also does it come back on cleanly or does it progressively go from rough to clean? That will help point us in the right direction.

Larry
 
Thank you for this valuable information.

It seems that the engine immediately stops, as if it goes from normal power to no power to normal power in a half a second, similar to what would be expected by switching the mags off. No roughness is noted beforehand and just a hint afterwards for a brief period.

This information thread has caused me to stop and reflect on whether this occurs only on the right tank. I have never found water in it, but I have found dirt. And due to a heavy right wing I spend more time flying on the right tank.

Sounds like some flying is in order on the left tank and see if I experience this. It occurs infrequently so it will take a bit of time. In the meantime I suppose I could at least keep good notes on what tank it does occur on when it happens.
 
yep, water droplets in your fuel could be a reason (happened to me on another aircraft).
 
Since you say it goes from normal power to no power and back to normal power in a 1/2 second - it is possible that you have a valve that is hanging up.
I know this is not a total power failure, but over a short period of time it will sound and feel like a total drop in power.
 
stay over the airport - talk to an A&P

... I have never found water in it, but I have found dirt. And due to a heavy right wing I spend more time flying on the right tank.

Sounds like some flying is in order on the left tank and see if I experience this. It occurs infrequently so it will take a bit of time. In the meantime I suppose I could at least keep good notes on what tank it does occur on when it happens.
I'd recommend debugging this within gliding range of an airport. Might also get a good A&P to give you a hand to make sure that the dirt you saw is not still resident in your fuel system. Could be clogging a filter or a jet in the carb.
 
I'd recommend debugging this within gliding range of an airport. Might also get a good A&P to give you a hand to make sure that the dirt you saw is not still resident in your fuel system. Could be clogging a filter or a jet in the carb.

Thank you. This is an injected motor.
 
part number?

Is it a carb'd O-360 engine? If so what P/N carb do you have? Maybe one that causes that type of scenario. 10-3878 is a common carb that has been known to cause that type of issue. 10-4164 or 10-3878M are good P/N's that don't normally do it. Could be a bunch of things but 10-3878 carb definitely can cause intermittent, momentary hiccups like you describe.
Good Luck,
Mahlon

where would one look for the part number on the carb?
 
Its the lightspeed ignition...

For the last 25 hours, since I finished the condition inspection, about five times now, when cruising or descending, the engine stalls out for just a split second and then comes back alive. By the time one can react, it's back and purring.

I changed the spark plugs at the last condition inspection and did a compression check (78, 78, 79, 80). Oil analysis was good.

Pmag and Lightspeed ignition.

Should I change out my plugs again? Or any suggestions where to start? Prior to the RV flying it's been 25 years since I flew. I have about 50 hours on it now. Maybe this is not abnormal and I have forgot about it? Absolutely no other trouble indications.

I had the exact same problem in my Long EZ when it had about 25 hours on it (O-320, 1 mag, 1 Lightspeed Ignition). I could never be duplicate on the ground. It gets your attention really quickly.

I had the mag and the carb rebuilt (but there was nothing wrong with either of them). I finally reached out to the canard community and got a PM that said to get rid of the Lightspeed ignition... it was the problem. This is a little confusing because we have two ignitions and the other should keep the engine running just fine. I think it is a spark timing issue with the computer losing its mind momentarily and screwing up all cylinders simultaneously (read on).

Talking to Klaus (as if anyone can actually talk to Klaus...), he told me it was my problem because the ignition was out of warranty, because it took me a couple of years to finish the plane after I had purchased the unit. He doesn't go by hours on the unit... I removed it, and installed the original magneto in its place. The problem never happen again. I eventually replaced the mag with a Pmag and still never had this repeat. Reinstall the magneto and see if that fixes your problem.

People have also had a lot of problems with the coils. However if you are experiencing a complete power loss, its probably the brain.

MTCW
 
I had the exact same problem in my Long EZ when it had about 25 hours on it (O-320, 1 mag, 1 Lightspeed Ignition). I could never be duplicate on the ground. It gets your attention really quickly.

I had the mag and the carb rebuilt (but there was nothing wrong with either of them). I finally reached out to the canard community and got a PM that said to get rid of the Lightspeed ignition... it was the problem. This is a little confusing because we have two ignitions and the other should keep the engine running just fine. I think it is a spark timing issue with the computer losing its mind momentarily and screwing up all cylinders simultaneously (read on).

Talking to Klaus (as if anyone can actually talk to Klaus...), he told me it was my problem because the ignition was out of warranty, because it took me a couple of years to finish the plane after I had purchased the unit. He doesn't go by hours on the unit... I removed it, and installed the original magneto in its place. The problem never happen again. I eventually replaced the mag with a Pmag and still never had this repeat. Reinstall the magneto and see if that fixes your problem.

People have also had a lot of problems with the coils. However if you are experiencing a complete power loss, its probably the brain.

MTCW

I have had a mag fail and also often drop one mag in flight for testing. Losing one ignition system creates a small drop in RPM/power and causes the EGTs to rise. Losing one ignition system WILL NOT cause an engine to stop working for even a brief second. To get the symptoms described by the OP, BOTH ignitions would have to stop working. It is possible that the PMAG is not working and a brief drop out of the LS would cause this. However, assuming the OP does mag checks before TO, this seems unlikely.

I just don't see how one ignition can keep the other from properly lighting the charge, creating a "no fire" scenario across ALL cylinders. Having one ignition too far advanced can cause rough running and misses, but it usually lights it early (rough running and/or detonation) or, if too far advanced, not at all (cyl runs fine on other ign). The charge won't ignite untill a minimum level of compression has been applied.

Larry
 
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Talking to Klaus (as if anyone can actually talk to Klaus...), he told me it was my problem because the ignition was out of warranty, because it took me a couple of years to finish the plane after I had purchased the unit. He doesn't go by hours on the unit... I removed it, and installed the original magneto in its place. The problem never happen again. I eventually replaced the mag with a Pmag and still never had this repeat. Reinstall the magneto and see if that fixes your problem.

Klaus had a problem with some of his Plasma II boxes. A transistor was not well-mounted, one of the leads would crack and would cause a miss. I agree he should fix them without charge but nevertheless he will check and fix them if they're bad. I have also had a coil go bad so I keep a spare, Nology PFC-06D here https://www.nology.com/profireauto.html
 
Once upon a time many moons ago, I had a similar problem with ElectroAir ignition system. My engine would "Hic-Up" at about 400' altitude on the first take-off of the day. Never able to repeat the problem at any altitude or any other time.

Jeff Rose worked with me even though the system was out of warranty.
We replaced each component of the system one at a time. Nothing helped. Jeff said that, "It can't be the system because we have replaced every part." However, with the system removed and the magneto reinstalled, the problem never surfaced again.

Jeff bought the system back. (Again even though it was out of warranty). To my knowledge, he never found the problem. Every individual part passed all tests.
Jeff Rose was a Great guy!
 
Mel,
I had the exact same problem with my Jeff Rose ignition system in my RV6 (circa 2000). An early problem we had was with a magnet that had come loose in the Hall effect unit. Jeff fixed that, but the problem persisted. The final straw was when my engine just quit completely, for a few seconds still during my phase I flight test. My other ignition system was a Bendix mag (just overhauled) that also quit at the same time. I had enough and told Jeff I didn?t want to be a flight test pilot on his new system. He refunded most of my money and I bought two new Slick mags - not much better, but they lasted until I sold the plane without a problem. EI?s have come a long way since then.
 
Check cheap stuff first

Not an engine guru but I'd check the ht wires and the ignition switch first. Also the associated wiring. Look for wires that may have worn due to rubbing on an adjacent surface or simply come loose. I'd consider your symptoms as a 'warning' from your electrical system that something is going wrong. Cheap stuff first. Please let us know what you find.
 
For the last 25 hours, since I finished the condition inspection, about five times now, when cruising or descending, the engine stalls out for just a split second and then comes back alive. By the time one can react, it's back and purring.

Do you have an engine monitor that stores data? That info might be helpful in seeing what is happening during the event.
 
From your OP it sounds like the issue began after your most recent condition inspection, and never occurred before that. If that?s the case, then if it were me, I would look closely at everything that was ?touched? during the inspection. Maybe I am just stating the obvious, but...
Hope you find the smoking gun, and please report back.
Good luck
 
I have had a mag fail and also often drop one mag in flight for testing. Losing one ignition system creates a small drop in RPM/power and causes the EGTs to rise. Losing one ignition system WILL NOT cause an engine to stop working for even a brief second. To get the symptoms described by the OP, BOTH ignitions would have to stop working. It is possible that the PMAG is not working and a brief drop out of the LS would cause this. However, assuming the OP does mag checks before TO, this seems unlikely.

I just don't see how one ignition can keep the other from properly lighting the charge, creating a "no fire" scenario across ALL cylinders. Having one ignition too far advanced can cause rough running and misses, but it usually lights it early (rough running and/or detonation) or, if too far advanced, not at all (cyl runs fine on other ign). The charge won't ignite untill a minimum level of compression has been applied.

Larry

Yeah... I know it doesn't make sense. But if you replace everything else and the problem doesn't go away, and then replace the ignition and it goes away... that kind of says its the ignition.

I had heard about the taller components on the Lightspeed's circuit board would break and that adding RTV to them stopped that from happening (Klaus never addmitted this was ever a problem). The thought was that all cylinders would fire at the same time. I'm not sure what that would sound like or feel like.

I recall one of the canard guys telling me that I should expect a certain amount of infant mortality in these things. When Klaus' infant mortality turns into my mortality, no thanks.
 
I have dual PMAG and I can change the timing of both PMAGs in the air. I believe the process is that it sends timing to one PMAG and then to the second one. When I do that, the engine for just about a half a second to a second drops, it is more like you see it in the RPM that drops about 50-70 RPM.
I wonder if this is how your perceived engine drop is and if so, if something is happening with one mag dropping and coming back alive.
 
I have dual PMAG and I can change the timing of both PMAGs in the air. I believe the process is that it sends timing to one PMAG and then to the second one. When I do that, the engine for just about a half a second to a second drops, it is more like you see it in the RPM that drops about 50-70 RPM.
I wonder if this is how your perceived engine drop is and if so, if something is happening with one mag dropping and coming back alive.

You are correct, your EIC sends the new configuration to one ignition, waits 30 seconds, then sends it to the second igntion. This is because the new configuration interrupts the firing for a split second. Long enough that if it changed the timing on both at the same time the exhaust would load up with unburned fuel. Then when both ignitions come back on line, it would burn off that fuel with a BANG. By staggering the configuration updates, there is never a period when unburned fuel gets dumped in the exhaust. However, we can't stop the momentary sag as each ignition goes offline to load it's individual update.
 
It is unlikely to be your ignitions.

Since you didn't mention any backfire when it comes back on line, I would suspect fuel delivery.

I would second this and look into fuel or fuel contamination...I had this once on 2 different Cessna aircraft but a year apart and it was in both times directly after getting fuel. Both times it put me in full emergency adrenaline mode but your guess is as good as mine.
 
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Isolate your mag switches (i.e. hot mags) and go fly.

I have resolved a problem like this before....never found the thing that shorted two mags together but isolating one mags taco wire fixed it. I assume an EMS fault or a wire strand somewhere.....

Start with basics.
 
P mag--Had a loose wire in the three wire connector from the coil to mag body was very hard to isolate finally got worse over time. Was inconsistent and uncomfortable for sure. Check those wires at the P mag connectors!??
 
I look around under the cowling for any possibilities.

-Spark plugs are in tight.
-Magneto looks good.
-Sampled fuel, and it does not appear to be contaminated.
-Traced lightspeed wiring and did find an obvious bad ground

Flew the airplane at 8,500' overhead the airport, and in the vicinity of the airport.. no issues.

Question is, would a bad ground potentially cause the momentary stumble that I saw? The problem is intermittent enough that I can't say it's solved, but that bad ground sure makes me wonder.
 
Question is, would a bad ground potentially cause the momentary stumble that I saw? The problem is intermittent enough that I can't say it's solved, but that bad ground sure makes me wonder.

Quite possible. A bad/loose ground is no different than a bad/loose power wire. The circuit must be complete.

A customer of mine had dual LS Plasma II installed on his -7 when he bought it. After several troubleshooting sessions and connector cleaning, a call to Klaus determined that the hall effect module(s) had known issues that he could fix for $300 each. He is now running dual P-Mags and the LS stuff is on a shelf. No problem since.
 
I look around under the cowling for any possibilities.

-Spark plugs are in tight.
-Magneto looks good.
-Sampled fuel, and it does not appear to be contaminated.
-Traced lightspeed wiring and did find an obvious bad ground

Flew the airplane at 8,500' overhead the airport, and in the vicinity of the airport.. no issues.

Question is, would a bad ground potentially cause the momentary stumble that I saw? The problem is intermittent enough that I can't say it's solved, but that bad ground sure makes me wonder.

A mag only uses a ground on the P lead to STOP sparking. It does not need a ground or P lead in order to spark.
 
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Is it a carb'd O-360 engine? If so what P/N carb do you have? Maybe one that causes that type of scenario. 10-3878 is a common carb that has been known to cause that type of issue. 10-4164 or 10-3878M are good P/N's that don't normally do it. Could be a bunch of things but 10-3878 carb definitely can cause intermittent, momentary hiccups like you describe.
Good Luck,
Mahlon

any cure for the 10-3878 carb issues other than replacement?
 
Engine woes

Wouldn?t hurt to really drain the wing sumps to rule out any contamination in the fuel. That little squirt in the sample cup can?t accomplish what follows. ALL FUEL HANDLING PRECAUTIONS APPLY. Elevate 1 wing a little. I use a spot outside the hangar where I can get a main tire off the edge of ramp into the grass. Ground everything together and to a ground point. Remove the wing quick drain from that elevated wing and drain 1-2 gallons into a clean bucket. Crack or remove the gas cap to get max flow. Repeat for the other side. Ensure the fuel vents are clear. Next I would check that the carb body screws are tight then drain the carb bowl to check for contaminates. If you into a little overkill take off the fuel supply flex line between the firewall and engine pump, sight thru it toward a bright light to check the liner is smooth and doesn?t have any ?flaps?. If this line is too stiff to straighten out for this check consider replacing it.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
I scanned this thread and didn't see anyone mention the possibility of a clogged fuel vent. If this is only happening in flight on one tank, and that tank's vent line is plugged it can disrupt fuel flow. I had this problem, fuel pressure would drop drastically and engine would stumble a bit. It wouldn't last long. Engine certainly didn't quit, but it was concerning. In my case it was a clogged screen, from sloppy adhesive application.

I'll get a similar, but far less dramatic effect with very full tanks. Seems that it only happens when I haven't burned enough fuel to reach the vent port in the root of the tank.
 
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