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IO-360 - All 4 EGTs/CHTs oscillating together, slight roughness. Looking for ideas.

C

Cwarkenton

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Hi everyone,
I'm hoping to get some ideas before taking the airplane back to my shop.
Airplane
Van's RV-7
Lycoming IO-360 (parallel valve)
Hartzell constant-speed prop
Dynon HDX EMS
Slick magnetos
History
This issue originally started several months ago when the manifold pressure sensing line to the Dynon manifold pressure sensor broke.
The line was repaired and issue was remedied.
Now the airplane just came out of annual, during which the shop:
Installed new spark plugs
Installed a new ignition harness
Relocated the Dynon manifold pressure sensor from inside the cabin to the engine side of the firewall
Completed the annual inspection and other miscellaneous maintenance
Unfortunately, the original symptom is still present.
Symptoms
Slight but noticeable engine roughness in cruise when event occurs.
All four EGTs and CHTs oscillate together rather than one cylinder acting independently.
MAP and RPM appear very stable.
Fuel flow appears to fluctuate slightly (around 0.1 GPH), although I'm not sure whether that's significant.
Dynon will occasionally switch between displaying ROP and PK, even though I'm indicating approximately 50-80°F ROP.
GAMI spread is approximately 0.44 GPH.
CHTs otherwise look healthy and fairly even.
Engine starts well and appears to make normal power.
Separate electrical issue
Also after the annual, I'm now seeing charging voltage fluctuate between about 14.5 and 15.0 volts. This was not occurring before the annual. My shop believes the alternator's internal voltage regulator is failing, and we've already ordered a replacement B&C alternator.
I don't know if this is completely unrelated or if electrical noise could somehow be contributing to what I'm seeing on the EMS, but I thought it was worth mentioning.
I attached in a video in below comment.
Questions
Has anyone seen all four cylinders oscillate together?
Could this still be related to the manifold pressure sensing system or relocating the sensor?
Does this point more toward ignition timing, fuel servo, induction, or something else?
Could a failing alternator/regulator contribute to this behavior, or is that likely an unrelated issue being that originally the event occurred from a broken MP line?
Thanks in advance. Any ideas or troubleshooting suggestions are greatly appreciated.
 
Last edited:
lr172 said:
CHTs simply don't move that fast. You have an indication issue.
Click to expand...
Thanks! This was my first thought as well however there is slight but noticeable roughness when the oscillation occur.
Originally thought you put 'induction' issue which is kinda what I'm thinking but I am very inexperienced in engine issues.
 
Check your engine monitor grounds.
Check the EGT CHT d-sub connector at the engine monitor.
Get your indication issues resolved first, than address any perceived engine issues.
 
Last edited:
Cwarkenton said:
Thanks! This was my first thought as well however there is slight but noticeable roughness when the oscillation occur.
Originally thought you put 'induction' issue which is kinda what I'm thinking but I am very inexperienced in engine issues.
Click to expand...
well, there certainly could be something else going on as well, but whatever that is, it is not causing the chts to bounce like that. Do you have elec ignition? A systemic power or ground issue could be messing with that as well and creating the roughness.
 
The Dynon EMS indication of ROP, PK or LOP reflects a software model of your engine, not reality. It tends to be close, good enough for ball park stuff, not good enough as an analysis tool. As others have noted it seems you have indication problems, so inputs to this software model are now suspect as well.

With a GAMI spread of 0.44 and you running that low in the ROP range I’d guess you may have one or more cylinders LOP while others are ROP. This may explain your engine roughness. The preferred options it to reduce the GAMI spread to 0.0 - 0.1 GPH. This is not hard. I suggest that you never put a bigger nozzle in the lean cylinder(s), aways approach this by going smaller in the rich cylinder(s). My experince is 1 or 2 nozzle changes over 3-4 data runs and you are done. Don Rivera at AFP will help if you call him. I also recommend not spending money on GAMI nozzles.

Carl
 
lr172 said:
well, there certainly could be something else going on as well, but whatever that is, it is not causing the chts to bounce like that. Do you have elec ignition? A systemic power or ground issue could be messing with that as well and creating the roughness.
Click to expand...
Don't like the fluctuating voltage. possible that is the source of moving chts if it is adding interference on the bus, but don't really see how that could create roughness with slick mags.
 
lr172 said:
any chance the roughness is the alternator loading up and letting go in oscillation?
Click to expand...

....maybe....

If the OP had a hand held O-scope, configured correctly (AC coupled), I'll bet the mains look as "rough as a corn cob" (lots of AC transients riding on top of the DC).

+1 for the Alternator - Regulator, secondarily look at the rectifier - one or more failed?
 
Thanks you guys! I'm getting some good info and I appreciate it!
A note I should have included is that the oscillation event seems sporadic. At times everything it runs completely steady then it seems to randomly happen which is why I know there is a slight roughness. I feel a different vibration at my feet, check the monitor and sure enough everything is reading sporadically.
 
Cwarkenton said:
Thanks you guys! I'm getting some good info and I appreciate it!
A note I should have included is that the oscillation event seems sporadic. At times everything it runs completely steady then it seems to randomly happen which is why I know there is a slight roughness. I feel a different vibration at my feet, check the monitor and sure enough everything is reading sporadically.
Click to expand...
given that the roughness appears with the fluctuating voltage and other indication anomolies, i would start by sorting out the charging system first. start with the easy stuff, maybe loose wires on alt (pp has major issues with that), engine grd strap, etc.
 
bjdecker said:
....maybe....

If the OP had a hand held O-scope, configured correctly (AC coupled), I'll bet the mains look as "rough as a corn cob" (lots of AC transients riding on top of the DC).

+1 for the Alternator - Regulator, secondarily look at the rectifier - one or more failed?
Click to expand...
i was thinking that a loose wire on the sense side could causing the alt to intermittenly go full output, then back off. could see how the inexperienced could view that as slight roughness. the rouighness tracking with weird indication issues makes this possible, as there is not many other ways for elec issues to cause roughness with mags.
 
If engine data recordings are available, we might be better able to determine cause-and-effect. Eg, if variations in the alternator voltage don't line up timewise with anything, we would look elsewhere.
 
Thank you all for the replies! I'm going to check all wiring and grounds over the weekend. That sounds like the consensus. Will report back!
 
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