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  #1  
Old 10-25-2016, 08:09 PM
Aggie78 Aggie78 is offline
 
Join Date: May 2014
Location: Fort Worth, Texas
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Default Engine Stumble Help Requested

Howdy Gang,

Having a problem diagnosing this engine stumble...Cylinder #2 appears to lose power:







I've kind of ruled out ignition system as a source due to cleaned plugs and a newly installed P-mag (10 hours ago). A little richening of the mixture and she smoothes right out and runs good, even leaned back out to the same degree.

Had the FF nozzles cleaned out a year or so ago, but did have the servo re-flowed earlier this year and wondering if gunk from that could be in a restrictor?

Thinking about swapping restrictors around as a first step unless someone has a better idea of something else to do first?

Thanks,

Rob
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  #2  
Old 10-25-2016, 08:37 PM
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AltonD AltonD is offline
 
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Location: Dothan, Alabama
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In flight mag check?
EGTshould go up when you do. The spike tells me one plug is miss firing.
When I first swapped to pmags, I had the same issue. I got religious about leaning while taxing. I also had to adjust my full rich mixture. It was very rich. You should see 50-100 rpm increase when you pull the mixture on shutdown.

Replace both plugs, clean the injector nozzle, restrictor.
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  #3  
Old 10-26-2016, 08:40 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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It does not seem to be ignition (at least lower down the probability list), as it responds to increased fuel. You will notice that it does not fully recover with more fuel, though I don't know your engine. Notice that #2 is the second highest EGT in the beginning. After recovery, it is the lowest.

I would be looking at fuel flow and blockage, especially with a history of this problem. I would pull the #2 restrictor for cleaning and would also flush the SS line. If it persists, I would flush the whole system.

Given the FF, I assume you are running LOP at the time. My guess is that #2 gets restricted (a piece of junk floating around that blocks flow to different degrees at different times) and net #2 flow drops. This causes the miss or lack of firing. The increased gross flow gets it firing again, but is still more lean (net flow is still lower than normal) than it was before the event, as evidenced by your logs.

Larry
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  #4  
Old 10-26-2016, 09:47 AM
tim2542 tim2542 is offline
 
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Location: Redding,Ca
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When you had the servo serviced did they also do the flow divider? I have trouble imagining that nozzles could plug and then unplug repeatedly. It seems more like junk in the flow divider to me.

You can see a little egt spike on #2 before it drops off when the fuel flow is increased from what appears to be the LOP condition. So it appears that cylinder is peaking well before the others.
Have you done a GAMI spread test on it?

Another thought is an intake leak.

Good luck
Tim Andres
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  #5  
Old 10-26-2016, 10:01 AM
Kyle Boatright Kyle Boatright is offline
 
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Your comment about it responding to increased fuel makes me think induction leak.
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  #6  
Old 10-26-2016, 10:06 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by tim2542 View Post
When you had the servo serviced did they also do the flow divider? I have trouble imagining that nozzles could plug and then unplug repeatedly. It seems more like junk in the flow divider to me.

You can see a little egt spike on #2 before it drops off when the fuel flow is increased from what appears to be the LOP condition. So it appears that cylinder is peaking well before the others.
Have you done a GAMI spread test on it?

Another thought is an intake leak.

Good luck
Tim Andres
According to the logs, the problem occurred on three different occasions and always occurred on #2. I don't see how random blockage in the divider could always occur on the same cylinder. If the debris were stuck in the V slot of the divider's #2 outlet, it would not be intermittent at the same flow. If it is floating around in the divider chamber, the odds of it blocking the same port on three separate occasions are pretty low. The cylinder/piston in the divider creates a wiping motion over the v slots, opening and closing them based upon fuel pressure. The only blockage that can occur there over a period of time would be that which becomes stuck in the slot and does not protrude into the interior. I don't see how that type of blockage could be intermittent at constant fuel flows.

Just my thoughts. Clearly cleaning out the divider in this case is good advice.

Larry
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Last edited by lr172 : 10-26-2016 at 10:10 AM.
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  #7  
Old 10-26-2016, 10:47 AM
BillL BillL is offline
 
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Location: Central IL
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Just another opinion, but . . .

1. Intake leak -maybe possible, but since it is injected the fuel/air would be richer if there was a leak AND at WOT a leak has little effect anyway. = Not likely the issue, move on.

2. Lower fuel flow - could be. A GAMI test, as mentioned, would verify this definitively (irrespective of ignition effects). = possible - do GAMI check first. If bad fix that, then consider other options.

3. As mentioned - inflight mag check would help. Also, a weak spark will push the lean misfire towards the richer mixtures. Plugs, gaps, wires, etc all have an effect, but it sounds like you are appropriately checking those. = Possible, but do a GAMI first to eliminate the fuel issue as you could chase ignition for a while.

Just one cent.
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  #8  
Old 10-26-2016, 11:30 AM
pa38112 pa38112 is offline
 
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It looks like you have your data on the Savey server - what do they say - That is what you are paying the for.
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  #9  
Old 10-26-2016, 11:42 AM
Ben Meyer Ben Meyer is offline
 
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Default Stuck Exhaust Valve?

Educate me, please. Is this not a stuck exhaust valve? Thanks in advance!

Ben
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  #10  
Old 10-26-2016, 11:53 AM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by Ben Meyer View Post
Educate me, please. Is this not a stuck exhaust valve? Thanks in advance!

Ben
I second that request. Same symptoms I had with an intermittent exhaust valve sticking on #2.
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