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  #41  
Old 12-27-2012, 12:51 PM
DakotaHawk's Avatar
DakotaHawk DakotaHawk is offline
 
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Location: Arlington, WA
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Here's the follow-up...

Last night I was able to follow up on a couple of the suggestions offered here.
  • I tested fuel tanks for water. No water found.
  • I checked all connections on Light Speed coils and plugs. No problems found.
  • I removed and cleaned the injector insert. Found some sooty colored black on the insert, but no blockage. All injectors looked good.
  • Checked intake gaskets and connector rubber for any intake air leaks. All tight.
  • Downloaded EMS data. Data shows a sharp spike of about ^300F on the #2 EGT about eight seconds after RPM went up to 2700rpm (take-off roll). About 2 seconds later, the #2 EGT dropped low (down to about 250F). Over the next 45 seconds, I reduced power to 1950 rpm, and then chopped power to land. When I chopped power, the #2 EGT picked back up and tracked with the other EGTs.

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  #42  
Old 12-27-2012, 01:46 PM
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Ron Lee Ron Lee is offline
 
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Many of the colors run together so it is hard to ID some things. There are lines at the bottom that may be the four CHTs. Is the one that drops below the others CHT #2? If so, and this in not the norm for your engine, there may have been a combustion related issue with #2.

Last edited by Ron Lee : 12-27-2012 at 01:48 PM.
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  #43  
Old 12-27-2012, 01:53 PM
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Mike S Mike S is offline
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That EGT line sure looks like an interruption to the fuel supply for that cyl from what I can see. Looks like a piece of crud got in the way, then let fuel through, then again partially blocked the fuel at the end.

Did you flow any fuel from the line when you had the injector orifice out??
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  #44  
Old 12-27-2012, 02:23 PM
BobTurner BobTurner is offline
 
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I agree with Mike, it sure looks like a partially blocked fuel line or injector. Not that there aren't other explanations. It looks to begin just prior to takeoff, perhaps taxiing onto the runway, where all EGTs went up a bit but #2 is much higher, running lean. At full throttle mixture is so lean (?) that it quits firing, EGT and CHT drop toward ambient (CHT slowly). After retarding throttle #2 starts firing again but is still too lean, high EGT compared to others. Looks like you added throttle to taxi, #2 briefly quits again, but comes back but still too lean after you reduce throttle.
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  #45  
Old 12-27-2012, 02:49 PM
BobTurner BobTurner is offline
 
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I would try the coke bottle test: remove all the injector line clamps (do not bend the lines), remove #2 and at least one other injector from the cylinder heads, put identical glass jars (coke bottles) under each injector, apply full throttle, full rich, turn on the fuel pump. Wait a minute or so, depending on the jar size, turn fuel pump off. Compare fuel levels in the jars. If #2 is obviously less than the others, you have a flow problem.
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  #46  
Old 12-27-2012, 04:01 PM
Tom Martin Tom Martin is offline
 
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A stuck valve could give the same readings. It happened, I believe, after a reduction of power. My experience with stuck valves has been on the ground, first start, and in the air after a power reduction.
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  #47  
Old 12-27-2012, 10:48 PM
N427EF N427EF is offline
 
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Hard to argue with experience Tom.
While you are correct in thinking that a stuck valve would result in the same kind of data read out, I believe a fuel problem is more likely.
Here is why:
DakotaHawk has been running mogas for some 500 hours by his own account and gumming up the valve stems with lead is somewhat unlikely, although possible. A stuck valve is almost exclusively the result of lead build up in the valve guide or on the valve stem.
Soooo, I think a plugged injector line even temporarily, has caused the rough running cylinder. I am also quite certain that this was not ignition related because of the almost ambient temperature reading on the EGT.
Having 2 ignition sources and one go out would elevate EGT's somewhat and having both go out at the same time on only one cylinder is highly unlikely.
My guess is an obstructed injector nozzle or line.
I don't think vapor lock or water contamination affects one cylinder only.
Let us know what you find, for educational purposes.
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  #48  
Old 12-27-2012, 11:29 PM
Lars Lars is offline
 
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Default stuck valve

I'm gonna stick with my stuck valve assessment. While I am certain (would bet substantial money on) that the only other possible explanation is a clogged injector, all the evidence Scott has presented looks exactly what I saw as I chased my issue. Every time it happened was after a reduction in power from wide open throttle and max rpm. One giveaway was in the post describing sooty exhaust stack on the offending cylinder, but not on the adjacent one. Fire is continuing, but it's happening in the exhaust stack, blackening it, rather than inside the cylinder where it belongs.

What will help with troubleshooting is if it happens again. If it's the same cylinder, repeatedly, as it was in my case, then it's not the injector nozzle.
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  #49  
Old 12-28-2012, 12:46 AM
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Mike S Mike S is offline
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Quote:
Originally Posted by Tom Martin View Post
A stuck valve could give the same readings. It happened, I believe, after a reduction of power.
Quote:
Originally Posted by Lars View Post
Every time it happened was after a reduction in power from wide open throttle and max rpm.
Look at the graph-------egt started up about 2 sec before throttle reduced, peak egt about a second before.

Not saying it isnt a valve, but if so, it was not after pulling power.
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  #50  
Old 12-28-2012, 04:53 AM
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rv8ch rv8ch is offline
 
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Default Sherlock Holmes

Impressive detective work going on here, gents. I don't have anything to add, except that this is really educational and entertaining. If anyone is not yet convinced that an engine monitor with logging is worth it's weight in avgas then they have not been paying attention!
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