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  #1  
Old 11-27-2017, 03:36 PM
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Kahuna Kahuna is offline
 
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Unhappy Stumped. Cylinder drops out at High MP.

This one has me absolutely stumped. Here is the deal.
I have an RV-8 with an 0-360 and AFP fuel injection system. Having a problem with #1 cylinder that seems fuel related. At high MP the cylinder drops off lean. At 24”Mp its fine. As I increase the MP, the EGT on Cyl#1 rises in direct correlation with the MP until the cylinder drops off. Here is what I have done to chase this problem down.
  • Overhauled servo and Flow divider.
  • Replaced engine monitor with new with new engine sensors.
  • Replaced Mags with electronic ignition
  • Moved injectors and inserts and rails around
  • Installed new cylinders!
  • Moved rails around to different pickups on flow divider.
Chart of the data here. (too big to paste in forum well)
Im stumped! And I dont get stumped easily. Nothing I have done has helped anything. I cant get the problem to move to another cylinder and even changing and installing new cylinders did nothing. On the chart data, Aux3 is MP. On take off, at just past 3min mark, I pulled MP back to keep EGT down and to prevent cylinder from dropping off. At 5.5min mark I increased MP and you can see cyl1 egt red color track up with MP until it drops off cold. At 9.5 and 10.5 & 13 min mark I slowly leaned to confirm cylinder was rich and would lean properly. At 14min mark I raised MP once again until cyl dropped off. Been chasing this for months now and Ive run out of things to do. Its acts like it has good fuel air mixture at 24"MP but then runs out of fuel as the air is increased with MP. Argh!
Thoughts and Ideas please.
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  #2  
Old 11-27-2017, 03:53 PM
F1R F1R is offline
 
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You could try a new injector LINE on the Cyl that drops at high MP.

Sometimes the ends are silver brazed and there can be a restricted flow compared to the others that does not present until peak fuel flow is required.

Or perhaps borrow / test a new flow divider.

Last edited by F1R : 11-27-2017 at 03:55 PM.
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  #3  
Old 11-27-2017, 04:13 PM
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JonJay JonJay is offline
 
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My goodness Mike. That is really frustrating.
What haven't you changed that is fuel/air related? Sump? Long shot but if there was a crack or something in that intake internal to the sump?
When you change cylinders did you change push rods? Lifters? Rocker arms?
Just throwing stuff out as I would have thought what you had already done would have yielded results.
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  #4  
Old 11-27-2017, 04:17 PM
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Kahuna Kahuna is offline
 
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Quote:
Originally Posted by F1R View Post
You could try a new injector LINE on the Cyl that drops at high MP.

Sometimes the ends are silver brazed and there can be a restricted flow compared to the others that does not present until peak fuel flow is ..
Yes tried that. Tried a new line and swapped lines around. Problem did not move. I have not tried a new divider since this one was rebuilt and bench for tested.
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Old 11-27-2017, 05:50 PM
vic syracuse vic syracuse is offline
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Wow. That's a tough one. It's interesting to me that it goes rich at the end when you are pulling the throttle back. A leak anywhere in the intake will usually cause it to go lean when you are closing the throttle.
Need some more details, unless I missed them---cold air induction? Burning any oil in that cylinder?

You say it drops off cold, but it looks like it is still firing to me, just lean. Does engine get rough?

Vic
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  #6  
Old 11-27-2017, 05:59 PM
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Default Hmmm.

Have you measured the cam lift on exhaust valve #1? I believe it is on its own lobe.

Thoughts:
1. It'd be helpful to see fuel flow on this data as well. I don't know if you can share the link to the interactive part of Savvy's site or not, without the risk of the data being corrupted.
2. The segment from about 11:00 to 14:30 or so is quite interesting. The high CHT at 14:00 would seem to indicate that #1 is running rich of peak, perhaps peak power, since anything lean of peak should drop CHT quickly. Again, seeing fuel flow at this segment might be interesting.
3. What happened with mixture right at the 13:15 or so mark? Cylinders 2,3 and 4 seemed to have peaked and begun their descent, but #1 perhaps hadn't yet peaked, given its sharp drop there.

Sure seems like #1 might be running rich, either too much fuel or not enough air (perhaps from restricted exhaust). Since you've swapped injectors etc., maybe that cylinder is not getting enough air charge.
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  #7  
Old 11-27-2017, 06:39 PM
molson309 molson309 is offline
 
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What airbox are you using?
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  #8  
Old 11-27-2017, 07:21 PM
scsmith scsmith is offline
 
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Did this engine and installation at one time function normally, or has this problem existed since initial installation?


I would think that anything that impaired the exhaust flow or intake flow to #1 would cause it to richen at high MP. Could there be something in the sump that would preferentially direct more air to #1? Hard to imagine such a situation.
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  #9  
Old 11-27-2017, 07:31 PM
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Kahuna,

Check connecting hose from intake to cylinder on bottom.

Cracked hose or failed clamp ??

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  #10  
Old 11-27-2017, 07:35 PM
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Kahuna Kahuna is offline
 
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Quote:
Originally Posted by JonJay View Post
When you change cylinders did you change push rods? Lifters? Rocker arms?
No those were kept the same.

Quote:
Originally Posted by vic syracuse View Post
Wow. That's a tough one. It's interesting to me that it goes rich at the end when you are pulling the throttle back. A leak anywhere in the intake will usually cause it to go lean when you are closing the throttle.
Need some more details, unless I missed them---cold air induction? Burning any oil in that cylinder?

You say it drops off cold, but it looks like it is still firing to me, just lean. Does engine get rough?

Vic
Standard updraft. Not burning oil (wasnt before) as I just changed all the cylinders hoping it would solve the problem. Only have 1 hr on them now. When I say it drops off cold, it looses power, misses, and cylinder goes cold. I did not leave it cold on this run. But that what it does. I have done so many flights now trying to diagnose and change this and that. Also since these are new cylinders with only an hour on them, did not want to abuse them. Just so Im clear, it did this with the old cylinder. This engine has 1700 hours on it, so I figured if I was going to change a cylinder to run this to ground, might as well change them all.

Quote:
Originally Posted by molson309 View Post
What airbox are you using?
Vans box. New air filter. No obstructions or alternate air.

Ive had a couple of people now mention lifters, cam and rockers. Im at a loss as how any of these items would give these symptoms. With a c/s prop and moving the throttle, not sure how the valves and lifters would come into play. But Im not that smart either.

Don at AFP would like to bench the flow divider again as well. But even this, Im not confident to find anything. Since ive moved rails and ports, how would the divider know to keep the problem on the same cylinder when I move the rail to a different port?

Here is the same data with FF. I added to the second chart on bottom half fuel flow in blue. Sorry could not add it to the top chart as the software does not allow it with the other data.

Keep the ideas coming. And maybe someone explain why cam/lifters/springs would come into play.
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