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  #1  
Old 03-19-2018, 02:40 PM
rjcthree's Avatar
rjcthree rjcthree is offline
 
Join Date: Jan 2007
Location: Bay Village, OH
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Default Cold (not dead) cylinder at high MP except WOT

I’m observing some behavior that I would like the group’s opinion on.

Setup: O-320-H2AD, 33H Hobbs/19.5H Tach since OH with new cam, lifters, new Lyc cylinders. Ellison, standard dual mag (D3000) also OH. Sensenich fixed, RV-9A. Compressions are 76/80 or better cold.

At full throttle/WOT – 28.5in HG for the most recent flight - at low altitudes (takeoff), CHT and EGT’s line up well. EGT’s are in the 1250F average range for what it’s worth, all rich of peak. At MP’s slightly below WOT to medium throttle – 27in HG to 20 in HG– cylinder #4 EGT falls by 100F-150F and CHT for #4 falls by about 30F-40F versus the average of the other three. The EGT falls fast and settles out with thirty seconds, CHT takes a couple minutes. Below 20in HG, all four cylinders come back together again in EGT and CHT quickly. It is repeatable, centering around 20in HG MP.

There really isn’t any perceived roughness, and even in this 27in - 20in HG cold-cylinder range, #4 EGT and CHT responds normally and consistently with the other cylinders to leaning, they are just doing so from a significantly different place. Since I lean to basically 100F-150F ROP at anything less than WOT, I can’t say if ranging from full rich to lean changes the behavior at the transition points. I believe it’s been occurring since hour 1.5 based on the data (no high power data exists prior to this time, <1.5H is all run-in), and there is no significant metal in the first two oil changes, suggesting I’m not wiping a lobe.

My first suspect is ignition, looking for one side of the ignition falling off on #4. I have not done any disassembly inspection yet, only gross inspection of the ignition harness - no obvious ignition leakage or damage to plug wires, and timing is on target. I did check the intake tube clamps (thanks Ralph, I should have mentioned it).

My plan: Run the Savvy ignition test in flight, in various levels of richness/leanness and MP’s. If it’s ignition, I expect it will show up pretty clearly, and the diagnostic work from there is (hopefully) logical: plugs, harness and magneto get the focus. I’ll probably look at the plugs anyway – a cylinder running that cold may be generating deposits that may point at something (one plug not firing being scuzzy?).

If that doesn’t give any hints, I will confirm my secondary elements: valve lift, boroscope, pushrods.

Any hints or past experience would be welcome. Thanks.
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RV-9A N183RC/90432: tip-up, O320H2, Ellison, Dynon D180, CPi2, Sen GA, at KLPR
RV-8 83718, wing kit, tanks done, with a four year plus plan - on hold due to home move
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Last edited by rjcthree : 03-19-2018 at 02:56 PM. Reason: Detail
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  #2  
Old 03-19-2018, 02:54 PM
Ralph Inkster Ralph Inkster is offline
 
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Location: Calgary, Alberta
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Add tightening intake tube clamps to your diagnostic list.
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  #3  
Old 03-19-2018, 03:52 PM
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Raymo Raymo is offline
 
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With #4 EGT and CHT falling, I'd suspect it is getting less fuel or more air than the others. If ignition was the issue, EGT would go up while CHT would drop (more fuel burning in the exhaust pipe).
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  #4  
Old 03-19-2018, 11:43 PM
simpkinsona simpkinsona is offline
 
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Default Normal?

Not familiar with the characteristics of the Ellison system, but I suspect it can have a wide variation of mixture between cylinders just like a carb. This is often a large difference and varies with throttle position. Probably normal.

-Andy
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  #5  
Old 03-20-2018, 06:17 AM
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rjcthree rjcthree is offline
 
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Location: Bay Village, OH
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Default More detail

I'm focussed on ignition from past engine experience and a whole lot of searching, and I'm not sure it's correct, but it's also what appears to be easiest to evaulate in a short local flight.

The oddity of it is the ability to turn it on and off. At 19.5MP, everything lines up, all CHT within 20F span, EGT's within 60F span. At 20.5 it's wonky, as described. At WOT, it's ok. I discounted mixture variation so far for two reasons - one is that even when #4 is deviated, it responds to mixture control in line (direction and magnitude) when adjusting mixture, so it's probably not gone past peak EGT or running LOP. The second reason is I have no idea what I can do to change it. It's already got the flow straitener, which may go away as part of later diagnostics if required.

Mentally, I'm wondering if #4 just isn't working that hard in this condition, and what could cause it. Oil pressure is >70psi thoughout, oil temp between 170F and 185F. Like Kahuna's post, back of my mind I'm thinking cam or lifter, but that it gets normal at WOT pushes that idea back to the secondary pile. The behavior is the same if it's at 2250 RPM or 2550 RPM.

It will come down to fuel, air, compression and spark, just like always. Ichikawa diagram time. Maybe it might be better to look at the two conditions EGT and CHT separately, then see what cross connects them, rather than assuming they are related.
Keep slinging ideas, I'll work the list. Thanks
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RV-9A N183RC/90432: tip-up, O320H2, Ellison, Dynon D180, CPi2, Sen GA, at KLPR
RV-8 83718, wing kit, tanks done, with a four year plus plan - on hold due to home move
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Last edited by rjcthree : 03-20-2018 at 07:04 AM.
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  #6  
Old 03-20-2018, 09:41 AM
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Tankerpilot75 Tankerpilot75 is offline
 
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Location: Oklahoma City, OK
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Default Not engine savvy

I?m certainly not the brightest person when it comes to engine diagnostics but here?s an idea. Check your sensors first. I have the GRT EIS system and experienced erratic EGT readings last year. After contacting GRT about the problem I purchased two replacement sensors (the second one just to have a spare).

Guess what. My spare was also immediately installed because I had more than one burned up sensor. CHT and EGT sensors are exposed to a lot of heat and pressure. They wear out. If the engine runs smoothly throughout the realms you expressed then I?d first check my sensors to ensure their not worn out and giving accurate information.

Just a thought.
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  #7  
Old 03-20-2018, 09:52 AM
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rocketbob rocketbob is offline
 
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Not enough development has occured with either the Ellison or the Rotec. Specifically the hole pattern and sizes of the holes in the spray bars are not correct for various throttle settings and neither is the venturi size for WOT. Since the Rotec is a copy of the Ellison, the same problems exist between the two. I have gotten the Rotec to work very well on the RV I fly but its still a work-in-progress.
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Last edited by rocketbob : 03-20-2018 at 10:16 AM.
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  #8  
Old 03-20-2018, 11:46 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by rjcthree View Post
I'm focussed on ignition from past engine experience and a whole lot of searching, and I'm not sure it's correct, but it's also what appears to be easiest to evaulate in a short local flight.

The oddity of it is the ability to turn it on and off. At 19.5MP, everything lines up, all CHT within 20F span, EGT's within 60F span. At 20.5 it's wonky, as described. At WOT, it's ok. I discounted mixture variation so far for two reasons - one is that even when #4 is deviated, it responds to mixture control in line (direction and magnitude) when adjusting mixture, so it's probably not gone past peak EGT or running LOP. The second reason is I have no idea what I can do to change it. It's already got the flow straitener, which may go away as part of later diagnostics if required.

Mentally, I'm wondering if #4 just isn't working that hard in this condition, and what could cause it. Oil pressure is >70psi thoughout, oil temp between 170F and 185F. Like Kahuna's post, back of my mind I'm thinking cam or lifter, but that it gets normal at WOT pushes that idea back to the secondary pile. The behavior is the same if it's at 2250 RPM or 2550 RPM.

It will come down to fuel, air, compression and spark, just like always. Ichikawa diagram time. Maybe it might be better to look at the two conditions EGT and CHT separately, then see what cross connects them, rather than assuming they are related.
Keep slinging ideas, I'll work the list. Thanks
hard to see ignition as the cause, given that the problem disappears at high MAP and low MAP. Seems a somewhat of a stretch to be a traditional fuel delivery problem either, given the symptoms, though I don't know the throttle bodies and their unique distribution issues. The fact that you can vary the mixture in concert with the other cylinders points away from the TB. Given the recency of the overhaul, I would be looking at something sticking or hanging up in the valve train or possibly something happening with the rings (issues with rings sometimes present differently at different load conditions). Drops in EGT/CHT can be related to reductions in power and not just fuel/air. For example, a valve sticking open will reduce the compression of the charge and therefore the power and heat output. The amount of leakage determines how much power/heat is lost.

Larry
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Last edited by lr172 : 03-21-2018 at 12:04 AM.
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  #9  
Old 03-20-2018, 11:47 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Raymo View Post
With #4 EGT and CHT falling, I'd suspect it is getting less fuel or more air than the others. If ignition was the issue, EGT would go up while CHT would drop (more fuel burning in the exhaust pipe).
less fuel/more air (i.e. leaner) than than the others while ROP would raise EGT & CHT. OP says he has similar readings at WOT / ROP. As throttle comes back, EGT drops. That would meant it is richer than the others, assuming you believed fuel/air was the cause for the drop.

Larry
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Last edited by lr172 : 03-20-2018 at 11:50 PM.
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  #10  
Old 03-21-2018, 09:54 AM
Canadian_JOY Canadian_JOY is offline
 
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I don't think this has been mentioned yet... One helpful diagnostic tool in a carb'd airplane is the carb heat control. A review of posts on this forum will reveal that some folks haven't been able to get even EGT's unless carb heat was used. Often it has been reported that only a small amount of carb heat was required to even things out.

Similarly, some owners report that more even mixture distribution is achieved by tipping the throttle butterfly slightly, or, in plain English, pulling back a small amount from WOT.

The turbulence caused by the throttle butterfly disrupting the airflow seems to aid some engines in smoothing out airflow within the intake runners. The same phenomenon might also be at play when some carb heat is deployed.

Others have also had success after installing a "flow straightener" between carb and intake.

If it's any consolation, our O-360 seems to exhibit similar but opposite symptoms, with #1 having higher EGT at all power settings when rich, and then the other three cylinders coming up to meet #1 as the mixture is leaned. It's weird... pull the mixture back and the EGT/CHT graph goes from a slope to a straight line. The joys of carburation!
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