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  #1  
Old 09-24-2012, 01:49 PM
Lars Lars is offline
 
Join Date: Nov 2005
Location: Davis, CA
Posts: 1,189
Default possible morning sickness?

I have a parallel valve Superior IO-360 in my RV-7. Vertical draft P/A Silverhawk fuel injection, 8.5:1 (180HP) pistons, dual Light Speed Plasma III ignitions, auto plugs (currently NGK BR8EIX), roller cam. Delivered new to me with 1 hour of dyno time in January, 2007. Sat pickled until first start in early June, this year.

The engine has always started easily, idles smoothly, with no signs of roughness on the ground other than the initial 1-2 seconds after it catches. Has only been run on 100LL. About 50 hours TTSN as of yesterday, oil changed regularly, burning about 1 quart in 25 hours now.

At about 5 hours of flight time, I was cruising at 6500', approximately 24 squared, leaned somewhat, when suddenly the engine started missing badly. After the initial panic and 180? turn back towards the airport (I was maybe 15 nm away at that point, airport is at sealevel) I noticed that CHT and EGT on #2 cylinder were dropping way off- it had gone completely cold. It was obvious that I was going to make the field, so I continued. Suddenly the cylinder came to life, as if nothing had ever happened. The symptoms reappeared as I was on downwind, but disappeared again by the time I was halfway through a 180 to final. Ran fine on the ground. My first thought was clogged injector, so I removed the line and the injector, checked for contamination. Found nothing. Reassembled, test flew, everything seemed fine.

A few hours of flight time later the problem reappeared, #2 cylinder again, once again it was only after I'd been flying for at least 15 minutes. Warm day, probably 80 degrees at altitude, but not scorching hot. That time it was intermittently less severe, but the cylinder eventually dropped off. During a beeline back to the airport it once again cured itself. Maddening, the worst type of problem to troubleshoot. This time I removed all the injectors, and, after calling Precision Airmotive, disassembled the flow divider to check for contamination. Found nothing. Ran fuel through the system with nozzles in glass jars which confirmed even flow. Swapped injector nozzles between #2 & #4 just in case, to rule that out. Reassembled, test-flew, everything was fine.

Yesterday, 35 hours after the last incident, the problem reappeared, intermittent in the air as always. Once again I returned to the airport and landed, only this time the problem continued intermittently on the ground. I ran it up to about 1500 rpm and watched the engine monitor. #2 would intermittently cut out (every few seconds) and when it did the EGT would drop precipitously. Once again I disassembled the fuel system from the flow divider on, but once again found nothing. I buttoned it up and test-ran it last night but didn't fly- it started and ran fine, all temps came up evenly.

Now I'm thinking about morning sickness, but I'm not sure what the symptoms are. It never happens at first start or when the engine is cold, but maybe that doesn't matter. What would one expect to see on an engine monitor? For what it's worth, I've checked compression, it's consistently 80/77 all around with a warm engine. Checked plugs, they looked fine everywhere yesterday. If an exhaust valve is sticking open, wouldn't EGTs go up instead of down?

I've spoken to a few local mechanics, but they don't have any ideas. I'm new to aircraft engines, but I've been working on ground-based engines my entire life, so I'm comfortable turning wrenches. I've read the description of the "rope trick" and I'm happy to do that if it makes sense.

Thanks in advance for any input!
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  #2  
Old 09-24-2012, 01:57 PM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
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Default

Have you tried replacing the plug on that cylinder? A bad plug can look fine. If that isn't the issue, try replacing the plug lead. If you're getting fuel and air into the cylinder, then it's gotta be the "fire".
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Last edited by Mark Dickens : 09-24-2012 at 01:57 PM. Reason: bad english
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  #3  
Old 09-24-2012, 02:07 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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50 hours is way too early to have valve sticking, unless there is something really odd. I'd look closely at the induction pipes. Could one of the rubber covered junctions be intermittantly opening up, leading to too lean misfire?
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  #4  
Old 09-24-2012, 02:12 PM
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DanBaier DanBaier is offline
 
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I wouldn't think of morning sickness. People often use that to describe when a cold engine is roughly running when started, but starts to smooth out. It's Lycoming's way of telling you to check the valve guides. If I've got the history of your engine correctly, and given the sudden on / off of the fault, it would seem very unlikely. I'd probably put that idea on the back burner.

Have you checked spark plugs & ignition leads? You might start by rotating the spark plugs to see what happens. It would be possible that you currently have two that are bad in the same cylinder. When you do a mag check they seem fine; yet when you push some power, at some point they break down (I've had this happen). That could explain why EGT is dropping - normally when one plug goes off and the other is still firing, EGT on the cylinder would rise.

You could also check the resistance of the ignition leads to see if there's some problem there.

Dan
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  #5  
Old 09-24-2012, 02:22 PM
Lars Lars is offline
 
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Quote:
Originally Posted by DanBaier View Post
I wouldn't think of morning sickness. People often use that to describe when a cold engine is roughly running when started, but starts to smooth out. It's Lycoming's way of telling you to check the valve guides. If I've got the history of your engine correctly, and given the sudden on / off of the fault, it would seem very unlikely. I'd probably put that idea on the back burner.

Have you checked spark plugs & ignition leads? You might start by rotating the spark plugs to see what happens. It would be possible that you currently have two that are bad in the same cylinder. When you do a mag check they seem fine; yet when you push some power, at some point they break down (I've had this happen). That could explain why EGT is dropping - normally when one plug goes off and the other is still firing, EGT on the cylinder would rise.

You could also check the resistance of the ignition leads to see if there's some problem there.

Dan
Thanks for the reply. Morning sickness seemed sort of unlikely to me, too, based on the descriptions I read. Especially considering the first time was at 5 hours.

I've checked plug leads, replaced plugs, etc. EGT always drops when this happens, along with CHT. In lockstep.

Also, a little more clarification: for anyone who isn't familiar, the Light Speed ignition systems are a "wasted" spark design" which means the plug fires on every rotation of the crankshaft. Each plug is fired from a coil that's shared with the plug on another cylinder, which means that if a coil goes bad it manifests itself as a misfire on both cylinders served by that coil.

Could be both plugs or leads going dead at the same time, which would mean that it's as you described, Dan, but since fuel would still be sprayed at that cylinder, wouldn't I expect a rise in EGT rather than a drop, and/or a big backfire when the raw gas ignited on its way out the exhaust valve?
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  #6  
Old 09-24-2012, 02:23 PM
Lars Lars is offline
 
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Quote:
Originally Posted by BobTurner View Post
50 hours is way too early to have valve sticking, unless there is something really odd. I'd look closely at the induction pipes. Could one of the rubber covered junctions be intermittantly opening up, leading to too lean misfire?
Yep, checked for that. All tight, in good condition Including nuts & gaskets at the cylinder head.
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  #7  
Old 09-24-2012, 02:28 PM
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N8RV N8RV is offline
 
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During your troubleshooting, be sure to check the quality of your connections to the LSE coils. I was doing a run-up earlier this year after flying the day before with no issues and when I turned off the mag, the RPMs dropped off drastically and one of the cylinders' temps dropped as well.

It turned out that the wire to one coil had broken from vibration where it attached to the connector. I replaced the connector (and reinforced the wires to prevent vibration) and figured that, if one wire was broken, the other one might be ready to break. Sure enough, all I did was touch it and it broke!

Just something to check.
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  #8  
Old 09-24-2012, 02:43 PM
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DanH DanH is offline
 
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I don't see any reason to discount valve sticking.
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  #9  
Old 09-24-2012, 02:47 PM
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Pmerems Pmerems is offline
 
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Default Call Bart at Aerosport Power

Bart should be able to help with the diagnosis. He has been very helpful even though I didn't purchase my Superior IO-360 from him. Give him a call.
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  #10  
Old 09-24-2012, 03:00 PM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by DanH View Post
I don't see any reason to discount valve sticking.
I agree.. find a local mechanic that can perform this Lycoming SB 388 -

http://www.caa.si/fileadmin/user_upl..._sb_SB388C.pdf
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