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  #1  
Old 01-16-2018, 11:33 AM
MK77 MK77 is offline
 
Join Date: Apr 2013
Location: Evanston, IL
Posts: 100
Default 4th flight engine issue

Hi All!

Just completed the 4th flight in my RV-7 on Sunday and experienced some variation in engine power that I hadn't before. It was very subtle actually, but I could sense by the sound of the engine and just feeling the acceleration / deceleration that the engine power was surging at times. Hard to detect in terms of engine RPM change, maybe around 50 RPM. After feeling it a few times I decided to head back to the airport to be safe.

I downloaded the engine data (below) and I noticed that on previous flights the EGTs for all cylinders were all very consistent (within maybe 30 deg of each other and tracking nicely). On this last flight cyl 1 and 2 were much higher than 3&4 for most of the flight. Occasionally they would come down to match the others for a brief period and then diverge again. First thing that comes to mind is an ignition issue. Perhaps one of set of plugs on cyl 1 and 2 weren't firing all the time, because that would cause an increase in EGT. Other thoughts?? Thanks in advance.

New Superior IO-360
1 LightSpeed II+ ignition
1 Slick Mag
Catto FP Prop

Flight 3 (no issue detected)



Flight 4

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  #2  
Old 01-16-2018, 11:54 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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After you eliminate any spark plug issues (just replace them to be sure), I would next look at:
- Intake air leak on #1 and #2 cylinders
- Injector clog
- Spider issue (do the simple shot glass fuel flow test)

After that, and assuming the mag/EI checks on runup are correct, then Id look at the LightSpeed.

Carl
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  #3  
Old 01-16-2018, 12:05 PM
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airguy airguy is offline
 
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1 and 2 are opposed cylinders, and share a single ignition coil for the lightspeed, that would be my #1 suspect. I doubt the induction leak or injection flow rates would change as cleanly and uniformly as they did, this looks like ignition.
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  #4  
Old 01-16-2018, 02:15 PM
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Walt Walt is online now
 
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Quote:
Originally Posted by airguy View Post
1 and 2 are opposed cylinders, and share a single ignition coil for the lightspeed, that would be my #1 suspect. I doubt the induction leak or injection flow rates would change as cleanly and uniformly as they did, this looks like ignition.
I think Greg nailed it.
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  #5  
Old 01-16-2018, 07:40 PM
deek deek is offline
 
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Location: Flathead Lake Montana - 8S1
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Carefully inspect the spade connectors on the coil, and the integrity of the BNC on the other end of the RG400 cable. If all seems okay, re-read the troubleshooting section of the LSE manual and then - and only then - call Klaus
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  #6  
Old 01-16-2018, 08:27 PM
MK77 MK77 is offline
 
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Thanks All! That reinforces what I was thinking. I'll run through the LSE troubleshooting and see what I come up with.
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  #7  
Old 01-16-2018, 08:35 PM
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N941WR N941WR is online now
 
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I'm confused, are all your numbers EGT's? What is going on with your CHT's?

If you have a bad coil pack, then both the CHT's and EGT's should be going down, not up.

If the LS is firing one coil pack out of time (is this even possible?), then you could see a rise in CHT and a drop in EGT or a drop in CHT and a rise in EGT.
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  #8  
Old 01-17-2018, 08:41 AM
sailvi767 sailvi767 is offline
 
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Location: Charlotte NC
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Be aware that a the coil light speed uses can work normally at sea level but fail at altitude. This caused us a long trouble shooting process.
G
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  #9  
Old 01-17-2018, 10:54 AM
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skylor skylor is offline
 
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Location: Southern California
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Default Dead Plug/ignition

Quote:
Originally Posted by N941WR View Post

If you have a bad coil pack, then both the CHT's and EGT's should be going down, not up.
Usually when one of the 2 plugs on a cylinder stops firing the EGT rises due to the slower mixture burn, and the CHT will drop.

Skylor

RV-8
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  #10  
Old 01-17-2018, 11:32 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by skylor View Post
Usually when one of the 2 plugs on a cylinder stops firing the EGT rises due to the slower mixture burn, and the CHT will drop.

Skylor

RV-8
+1
Losing one of two plugs in a cylinder will cause the "effective timing" to retard for that cylinder. This causes an increased EGT and decreased CHT. I also would be looking at the coil pack if it is shared by the two problem cylinders.

Larry
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