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  #1  
Old 05-07-2020, 10:23 PM
Earl Findlay Earl Findlay is offline
 
Join Date: Jul 2019
Location: Sandpoint, Idaho
Posts: 85
Default Engine momentarily dies

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.
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  #2  
Old 05-07-2020, 10:35 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,851
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No this is not normal.
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  #3  
Old 05-08-2020, 07:27 AM
Red Mtn flyer Red Mtn flyer is offline
 
Join Date: Jul 2017
Location: Carson City, NV
Posts: 128
Default

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.
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  #4  
Old 05-08-2020, 08:15 AM
mahlon_r mahlon_r is offline
 
Join Date: Jan 2005
Posts: 1,058
Default

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
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  #5  
Old 05-08-2020, 08:39 AM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 506
Default 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.
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  #6  
Old 05-08-2020, 08:49 AM
N941WR's Avatar
N941WR N941WR is offline
 
Join Date: Jan 2005
Location: SC
Posts: 12,887
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Quote:
Originally Posted by mahlon_r View Post
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.
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  #7  
Old 05-08-2020, 09:11 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,681
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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
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  #8  
Old 05-08-2020, 09:47 AM
Earl Findlay Earl Findlay is offline
 
Join Date: Jul 2019
Location: Sandpoint, Idaho
Posts: 85
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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.
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  #9  
Old 05-08-2020, 09:52 AM
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Dan 57 Dan 57 is offline
 
Join Date: Sep 2018
Location: LSZF
Posts: 795
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yep, water droplets in your fuel could be a reason (happened to me on another aircraft).
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  #10  
Old 05-08-2020, 10:19 AM
rag rag is offline
 
Join Date: Feb 2012
Location: Holmen, WI
Posts: 57
Default

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.
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