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Stumped. Cylinder drops out at High MP.

Kahuna

Moderatoring
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.
 
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.
 
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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.
 
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.
 
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
 
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.
 
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.
 
Kahuna,

Check connecting hose from intake to cylinder on bottom.

Cracked hose or failed clamp ??

Boomer
 
When you change cylinders did you change push rods? Lifters? Rocker arms?

No those were kept the same.

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.

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.
 
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.

When I purchased the plane this past summer it had this problem. Strangely, I did scope the sump looking for, I dunno what. Nothing was in there.

Kahuna,

Check connecting hose from intake to cylinder on bottom.

Cracked hose or failed clamp ??

Boomer

Hose and clamp replaced. Intake leaks manifest themselves at low MP pressures not high.
 
Does your airbox have the AFP ring installed?

My RV7 has AFP vertical induction. It's amazingly sensitive to disturbances in the airflow and it manifested itself on my airplane by the cylinders having very uneven mixture distribution. The uneven airflow in my case was caused by 2 things - the first was the original magnetic alt air door which would open at high power settings. The second was caused by the manual alt air door - just the slider Vans recommends - coming open when the cable came loose.

I think the lack of the "ring" could also cause airflow disturbances with some weird results. But yours is so sharp and focused on #1 it's hard to imagine that's what is causing it.

If you have a CS prop, have you tried raising MP when you're turning lower RPM? Any difference?
 
Does your airbox have the AFP ring installed?

I think the lack of the "ring" could also cause airflow disturbances with some weird results. But yours is so sharp and focused on #1 it's hard to imagine that's what is causing it.

If you have a CS prop, have you tried raising MP when you're turning lower RPM? Any difference?
Yes it has the ring properly installed. And yes its the same at lower RPMs
 
SNIP

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

The possible theory is the case where the exhaust valve isn't opening as far as it should (worn forward most cam lobe), it will restrict the exhaust cycle, which in turn might restrict air intake in that cylinder on the subsequent step. Fuel flow doesn't know this, so with less air it runs rich. Probably not the intake valve, as the same cam lobe runs intake on #2 as well IIRC.

Thanks for putting the fuel flow on the chart, it is helpful. It does indeed appear that you didn't hit peak EGT on #1 as you stopped leaning at about 13:15, where you again enriched the mixture. The other 3 cylinders had peaked, but not #1.

I don't know how the test is done on these engines, but removing the rocker covers and somehow measuring how much the exhaust valve moves vs spec, and vs the others, might tell a story.
 
I suggest measuring cam lift, if thats good, I would swap out lifter hyd units.

I don't know how the test is done on these engines, but removing the rocker covers and somehow measuring how much the exhaust valve moves vs spec, and vs the others, might tell a story.

I can remove the push tubes, and rods, collapse the lifters, reinstall, and measure the cam lift. Looking at this doc, where the heck is the tolerance for this?
 
Thanks for putting the fuel flow on the chart, it is helpful. It does indeed appear that you didn't hit peak EGT on #1 as you stopped leaning at about 13:15, where you again enriched the mixture. The other 3 cylinders had peaked, but not #1.

Yes. Cylinders less than an hour on them and trying not to abuse them. I was strictly looking to see that #1 was leaning as I pulled the mixture. Looking to assure I was ROP on #1.
 
I can remove the push tubes, and rods, collapse the lifters, reinstall, and measure the cam lift. Looking at this doc, where the heck is the tolerance for this?

Run to operating temp and remove #1 and #3 valve covers and read exhaust rocker travel for each cylinder with a dial indicator.
 
Although it is hard to understand how only a single cylinder would be effected, it is well known that a weak ignition system will cause problems at high power levels.

Perhaps wiring to that cylinder has been compromised somehow?
 
Lifters

Mike,

I had a lifter issue that would make my #1 cylinder go cold very quickly at higher engine power/rpm. Unfortunately we didn't get much data since the lifter locked up before we could troubleshoot. That caused the cylinder to go cold at all rpms. This was a factory new Superior so they tore it down, put new lifters in, built a new engine. 1300 hours now and still a very smooth engine.

Luckily yours is a Lycoming so you can pull the lifters if needed without splitting the case. I have one of the earlier Superior Roller engines that requires splitting the case to remove a lifter.

Came across this info online. Good read on "How Hydraulic Lifters Affect Valve Timing". I think I had a copy of this manual during my build but can't find it so getting the E-version from Spruce for $22.00.

https://books.google.com/books?id=J...I#v=onepage&q=lycoming lifter failure&f=false

Andy
 
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Although it is hard to understand how only a single cylinder would be effected, it is well known that a weak ignition system will cause problems at high power levels.

Perhaps wiring to that cylinder has been compromised somehow?

I thought that too. And this problem was on the mags, then I installed electronic ignition (dual) which of course was a complete gut of ignition system and the problem continued ruling the ignition out.

Mike,

I had a lifter issue that would make my #1 cylinder go cold very quickly at higher engine power/rpm. Unfortunately we didn't get much data since the lifter locked up before we could troubleshoot. That caused the cylinder to go cold at all rpms. This was a factory new Superior so they tore it down, put new lifters in, built a new engine. 1300 hours now and still a very smooth engine.

Luckily yours is a Lycoming so you can pull the lifters if needed without splitting the case. I have one of the earlier Superior Roller engines that requires splitting the case to remove a lifter.

Came across this info online. Good read on "How Hydraulic Lifters Affect Valve Timing". I think I had a copy of this manual during my build but can't find it so getting the E-version from Spruce for $22.00.

https://books.google.com/books?id=J...I#v=onepage&q=lycoming lifter failure&f=false

Andy

Excellent. Im going to be looking at this lifter over the next couple of days.
 
Excellent. Im going to be looking at this lifter over the next couple of days.

Is this thing constant speed or fixed pitch?

Three pages in, no mention of RPM change, just MP change. Lifters don't care about MP.
 
You might try a compression test (automotive style). It will show problems with cam timing, lobe profile and lifter problems.
 
Are these the same plug wires with all these changes, a leaner mixture requires more current to jump at the plug and ignite the mixture and a weak wire will not deliver the current to spark at a certain mixture. are the plug wires tied parallel, cross fire? or jumping to ground?
 
Are these the same plug wires with all these changes, a leaner mixture requires more current to jump at the plug and ignite the mixture and a weak wire will not deliver the current to spark at a certain mixture. are the plug wires tied parallel, cross fire? or jumping to ground?

He swapped mags for electronic ignition. It has all changed.

I also suspect it is a lifter problem, based on the information provided. How is the oil pressure looking during the test? Try a thicker (or thinner) viscosity oil, to see if it changes when the issue occurs.
 
He swapped mags for electronic ignition. It has all changed.

I also suspect it is a lifter problem, based on the information provided. How is the oil pressure looking during the test? Try a thicker (or thinner) viscosity oil, to see if it changes when the issue occurs.

I added the oil pressure to this chart bottom in Blue. No change in oil pressure during the occurrence. Working on testing the cam and lifter.
 
ignition wires? Loose connection?

Hey Mike:

I'm thinking ignition - change a few plugs around to see if it follows a plug. If not then a wire check is next, then have a look at the cap for proper attach and carbon tracking. Ignition can lay down with higher MP values...

This assumes that the cam (and the lifters on that lobe) are to spec, and the nut behind the wheel is tight.:D
 
ignition wires? Loose connection?

Hey Mike:

I'm thinking ignition - change a few plugs around to see if it follows a plug. If not then a wire check is next, then have a look at the cap for proper attach and carbon tracking. Ignition can lay down with higher MP values...

This assumes that the cam (and the lifters on that lobe) are to spec, and the nut behind the wheel is tight.:D
 
IIRC 0.350" is the number for a new lyc. cam to spec.

Also where is your oil pressure sensor feed tapped? IIRC Lycoming issued an SB or there was an online article that stated why new type certified ac with lyc instals had the oil pressure measured at the front end of the case, where the pressure will be lowest. There is a brass plug near the nose of the case, RH side actually by Cyl #1. I think that is where Lycoming now prefers the oil pressure to be measured. Perhaps it is not related to your issue, but it would be interesting to know what problems were manifesting that caused Lycoming to change their thinking on this.
 
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Instrumentation

Any chance this is an instrumentation issue? or can you tell there is something wrong just by listening?
 
Hey Mike:

I'm thinking ignition - change a few plugs around to see if it follows a plug. If not then a wire check is next, then have a look at the cap for proper attach and carbon tracking. Ignition can lay down with higher MP values...

This assumes that the cam (and the lifters on that lobe) are to spec, and the nut behind the wheel is tight.:D

Mags were replaced with electronic ignition.
 
I have sent the spider/flow divider off to AFP for them to re-check its function. Given my general understanding of how it works, and the testing done so far, I have no hope that there is any problem there especially after moving lines and ports and injectors and injector inserts around.

I completed a check of the cam, lifters, and dry tappet clearance per service bulletins and everything is within spec except the exhaust dry tappet clearance was slightly in excess (about .005) of the .080 allowed. Ill be installing a longer push rod as soon as I find one just to rule that out but I also dont have any faith that it would cause this problem.

Im still at a loss and Im still scratching my head. ARGH! Thanks for all the help and ideas so far.

:confused:
 
Hmmm...

SNIP . Ill be installing a longer push rod as soon as I find one just to rule that out but I also dont have any faith that it would cause this problem.
Im still at a loss and Im still scratching my head. ARGH! Thanks for all the help and ideas so far.
:confused:
I had to read this thread twice to understand that just about everything has been replaced on this one jug including the ignition system with the cylinder...So the three ingredients of fuel, air and spark... The only thing left after lifter travel or spider port is the intake riser for that jug? Wow,
I have seen a hard to find intake gasket issue manifest itself at mid and high power settings...head scratching...
 
Plugged up?

Restricted exhaust? If you have a muffler, maybe a broken baffle? I have seen a car exhaust that had a smaller pipe that collapsed inside a bigger pipe. Ran fine at Idle but had no power. Loooong shot I know but it sounds like you?re running out of boxes to check. Good luck!!
 
The pushrod being out of tolerance I doubt is the cause, seeing as you had the problem prior to replacing the cylinder.
Usually intake leaks don't affect the high power settings so much, and when they do it tends to go lean. This one almost acts like it is going rich. It certainly looks like it goes rich when you pull the power back at the end.
I see you took off the divider already. I would have been tempted to make a temporary injector line and swapped it with another cylinder to see if it moved. Don does really great work, so I would find the chances of it coming back from an overhaul and exhibiting the same problem a little remote.

I know you said you checked lifter clearances. Have you thought about swapping the lifters with another cylinder? I just wonder if one is collapsing under high power.

Vic
 
I know you said you checked lifter clearances. Have you thought about swapping the lifters with another cylinder? I just wonder if one is collapsing under high power.
Vic

Doesn't the lifter need to stay with the body it was broken in with?
 
I’m sure Vic is referring to the “hydraulic assemblies” they can be removed from the lifters and swapped around, but the individual components of the assemblies can not be mixed up.
This sure smells like a flow divider.
Mike, have you inspected the air vent holes in the injector bodies? Are the injector bodies clocked correctly?
If you have Turbo nozzles have you checked for blockage in the air lines?
Tim Andres

Edit: clocking only applies to nozzles installed in the lower ports
 
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I have sent the spider/flow divider off to AFP for them to re-check its function. Given my general understanding of how it works, and the testing done so far, I have no hope that there is any problem there especially after moving lines and ports and injectors and injector inserts around.

I completed a check of the cam, lifters, and dry tappet clearance per service bulletins and everything is within spec except the exhaust dry tappet clearance was slightly in excess (about .005) of the .080 allowed. Ill be installing a longer push rod as soon as I find one just to rule that out but I also dont have any faith that it would cause this problem.

Im still at a loss and Im still scratching my head. ARGH! Thanks for all the help and ideas so far.

:confused:

Pardon my ignorance of how this is done on a Lycoming, but for the check of the cam lift do you rotate the engine and measured how far the exhaust valve on #1 moves as compared to the others? Maybe this doesn't work with hydraulic lifters of these sorts, dunno. Or maybe the rocker is removed and the movement of the push rod is measured without the load of the valve spring?

The cam seems to be the only thing that hasn't been swapped or replaced, so it seems to be a likely suspect.
 
Any chance this is an instrumentation issue? or can you tell there is something wrong just by listening?

I think I read everything in the thread, but this is a good question that I've not seen answered yet. Do you feel it drop off or just see the data?

IOW, if you had no instrumentation on the motor, would you know anything is amiss?

If not, maybe switch the egt thermocouple and wiring completely to another cylinder and see what you get......
 
I?m sure Vic is referring to the ?hydraulic assemblies? they can be removed from the lifters and swapped around, but the individual components of the assemblies can not be mixed up.



That's exactly what I was referring to. You can take the hydraulic lifters out, keeping them assembled, and swap them with another cylinder.
 
I think I read everything in the thread, but this is a good question that I've not seen answered yet. Do you feel it drop off or just see the data?

It's there in post #10, by the OP:

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.
 
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IIRC 0.350" is the number for a new lyc. cam to spec.

Also where is your oil pressure sensor feed tapped? IIRC Lycoming issued an SB or there was an online article that stated why new type certified ac with lyc instals had the oil pressure measured at the front end of the case, where the pressure will be lowest. There is a brass plug near the nose of the case, RH side actually by Cyl #1. .

I wish I had known about that. The fitting just under the engine mount is such a pain to get to. I had to loosen the engine on its mounts to swap that out when I discovered damaged threads. I would have plugged it and gone with the forward location.
 
Mags were replaced with electronic ignition.

I've seen this behavior on my plane, and *only* on the electronic ignition (with one mag, one EI on the engine) The mag ran fine, the EI did not. Lower power/MP was ok, but once crossing the line things started to run very badly. It was very weird. In my case it was tired plugs and a couple of the ignition wires, high resistance -- and once replaced everything ran fine. It was a pain to troubleshoot though and we looked everywhere else before figuring it out. Even new plugs and wires can have that sort of problem sometimes.
 
I'm curious about what hypothesis would explain how anything in the valve train (e.g. hydraulic lifters) can tell what the manifold pressure is?

I can see if you had a worn cam lobe with reduced lift, it would run great at idle, and not put out much power at high MP because it can't breath ---just like an old Volvo B-20 or B-18, notorious for bad cam/lifter metalurgy and thus short cam life.

But this would not cause a sudden drop in power at some MP, it would just be a smooth gradual throttling effect.

Everything else in the valve train just keeps on turning no matter what the MP.
 
Kahuna,

Am I interpreting the fuel flow correctly? It seems that when you took off at about minute 3, you were burning about 16-17 gph, which is about right at full rich WOT.

But, then at about minute 5.5, fuel flow went even higher, to something like 20. This is of course right where #1's EGT went from about 1600 down to 1100, suddenly. Mixture too rich to support a normal combustion, it would seem.

Later, at about 13 minutes, where you were leaning, you achieved peak and were on the downhill LOP side of #'s 2, 3 and 4, but not #1. Even at your most lean point, you were burning 10 gph (again - am I mis-reading the chart?) at a MAP of about 24, which seems higher than it should be.

The 20 gph reading, if correct, seems to be out of line. Your #1 it appears is the richest cylinder, and might simply be the canary in the coal mine. Has Don Rivera seen this graph?
 
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