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  #31  
Old 12-02-2020, 07:46 AM
Walt's Avatar
Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
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Quote:
Originally Posted by RedRaider94 View Post
Walt, the Mag went through a 500 hour inspection and rebuild about 150 hours ago. It was sent off to Aircraft Magneto Service in Montana. I'm only a 5-10 minute plane ride from you so need to bring it by to let you take a look someday (I'm at Aero Country).
I probably have a mag laying around if you want to swap it out. Personally I don't think it would be hot fuel, under high power FF is high enough usually to avoid problems with fuel temps. One of the Ign systems IMO.
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  #32  
Old 12-02-2020, 08:13 AM
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rvmills rvmills is offline
 
Join Date: Nov 2007
Location: Georgetown, TX
Posts: 2,143
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Shawn,

Some thoughts from previous experience, that may help you eliminate bogeys:

My plane originally had a LS Plasma 1 and 1 mag. While that was installed, I had half a coil fail once, with a single errant EGT indication. Talked to Klaus, and he confirmed a coil can fail halfway like that, but it's rare.

I later had a brain box failure, which was intermittent, and only happened when cold. It was also an errant EGT. As the engine, and the box, which was on the cold side of the FW, warmed up, it went away. I changed plugs, wires, coils throughout, and finally sent Klaus the brain box. Klaus tested the box, and it was similar on the test bench. As soon as the box and all the transistors and gizmos inside warmed up electrically, it went away. He could also press on the box itself and it would go away before warming up. I know this is opposite of your situation, and you don't have EGT variances...just describing so you can either eliminate, or look at the box, if you develop other indications.

In a racing Glasair III, I had a slow degradation of a Romec mechanical fuel pump, which was masked by a boost pump also starting to go (yes...not a good situation, eh!). Changing the boost pump fixed FF issues at high power for a season, but they returned during the ensuing year. The manifestation of this was fuel pressure that dropped a bit and a hi EGT past a certain power setting. It was a turbo, so I'm talking very high power (greater than 50" MP). In the normal MP ranges the issue was not apparent, but I've been told that it would have been seen at lower power as the pump degraded further. New mechanical pump fixed it all. Your FF appears solid, so you may be able to eliminate this. However, its a parameter worth keeping an eye on, and perhaps it's worth testing to see if you see any RPM fluctuations at cruise power settings when hot.

I also had governor issues with that TIO-580 on the Glasair. Indications were RPM fluctuations, slightly higher in magnitude than yours, but not limited to when hot. an overhauled governor solved that one. The governor is an oil pump, so could hot oil unmask an internal governor issue...perhaps. Might be worth having it looked at.

Infant mortality on the overhauled mag may be unlikely, but not out of the question. Walt's swap offer isn't a bad idea. Just had similar happen on a Stearman mag. Mag bench tested good, so I troubleshot every other potential cause for 2 weeks, and we finally had a new mag built up...boom, fixed it.

Also agree that, while vapor issues could be present, if the configuration of fuel lines and injector lines hasn't changed, and its a new issue at 1500ish hours, this seems like a less likely cause. Have you looked for indications of cracks in the injector lines? I'd think this would cause other indications than just RPM flux (EGT primarily), but trying to help you rule out causes.

Good luck...these things can be hair-pulling...AMHIK!

Cheers,
Bob
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  #33  
Old 12-03-2020, 05:58 AM
RedRaider94 RedRaider94 is offline
 
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Location: Celina, Tx
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Thanks for all of the thoughts so far. I tried again last night and I feel like I have something going on with Cylinder #3. I have attached three recordings:

*** Note - the number 3 cylinder was replaced around 500-600 hours due to an SB on the superior jug. It was replaced with a superior head. The other three heads are the original Superior heads.

#1) After initial start and warming up. The plane was leaned aggressively for the warm up and I noticed on the monitor that #3 CHT was lower than the others but registering and the EGT's were significantly lower until it warmed up a bit. Don't know if this is typical as I have never noticed it before.

#2) 1st lap around the pattern. I did have some slight hesitations at full throttle so it did happen a little on the this flight but not a lot. What got my attention was how erratic the #3 EGT is around when I pull back on the throttle at the end of downwind. I have never seen this before.

#3) 2nd lap around (I taxied back to the runway with Fuel boost on the whole time to try and keep pressure high). I did feel the slight feeling of drop in power for a couple seconds followed by a slight surge in power then slight loss and slight surge a few times. The data though looks pretty clean on this run.

I am now pulling the last amount of hair I have out of my head. Worried this might be a valve problem on #3.

Again, I don't feel noticeable misses on startup. It has a good rhythm to it and doesn't shake or feel like anything is off.

I am getting concerned to fly it thinking something is really wrong with the #3 cylinder and it is going to throw a rod in flight or am I just overthinking this?
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  #34  
Old 12-03-2020, 07:30 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by RedRaider94 View Post
Thanks for all of the thoughts so far. I tried again last night and I feel like I have something going on with Cylinder #3. I have attached three recordings:

*** Note - the number 3 cylinder was replaced around 500-600 hours due to an SB on the superior jug. It was replaced with a superior head. The other three heads are the original Superior heads.

#1) After initial start and warming up. The plane was leaned aggressively for the warm up and I noticed on the monitor that #3 CHT was lower than the others but registering and the EGT's were significantly lower until it warmed up a bit. Don't know if this is typical as I have never noticed it before.

#2) 1st lap around the pattern. I did have some slight hesitations at full throttle so it did happen a little on the this flight but not a lot. What got my attention was how erratic the #3 EGT is around when I pull back on the throttle at the end of downwind. I have never seen this before.

#3) 2nd lap around (I taxied back to the runway with Fuel boost on the whole time to try and keep pressure high). I did feel the slight feeling of drop in power for a couple seconds followed by a slight surge in power then slight loss and slight surge a few times. The data though looks pretty clean on this run.

I am now pulling the last amount of hair I have out of my head. Worried this might be a valve problem on #3.

Again, I don't feel noticeable misses on startup. It has a good rhythm to it and doesn't shake or feel like anything is off.

I am getting concerned to fly it thinking something is really wrong with the #3 cylinder and it is going to throw a rod in flight or am I just overthinking this?
#3 EGT behavior points to an intake leak (goes lean with resulting higher EGT as the MAP goes down). However, that you should not have a significant impact at full power, only at low MAP regiments, such as idle to 1500. Quite unlikely this is causing your high power stumble. The leaking intake also accounts for the low EGT at idle. When the leak is moderate, as MAP starts to drop, the EGT rises. As the leak increase while you move towards idle, the EGTs will plummet.

Quite unlikely for a valve to stick for only 2 seconds in only highly repeatable, full power situations.

Larry
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Last edited by lr172 : 12-03-2020 at 07:42 AM.
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  #35  
Old 12-03-2020, 07:48 AM
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Lufthans Lufthans is offline
 
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Fuel starvation due to dirty gascolator (or other fuel filters you may have)?

I've fried a Ferrari engine that way :-(
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  #36  
Old 12-03-2020, 01:22 PM
pat76cj pat76cj is offline
 
Join Date: Jul 2020
Location: Western edge, Iowa
Posts: 31
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Quote:
Originally Posted by RedRaider94 View Post
Thanks for all of the thoughts so far. I tried again last night and I feel like I have something going on with Cylinder #3. I have attached three recordings:

*** Note - the number 3 cylinder was replaced around 500-600 hours due to an SB on the superior jug. It was replaced with a superior head. The other three heads are the original Superior heads.

#1) After initial start and warming up. The plane was leaned aggressively for the warm up and I noticed on the monitor that #3 CHT was lower than the others but registering and the EGT's were significantly lower until it warmed up a bit. Don't know if this is typical as I have never noticed it before.

#2) 1st lap around the pattern. I did have some slight hesitations at full throttle so it did happen a little on the this flight but not a lot. What got my attention was how erratic the #3 EGT is around when I pull back on the throttle at the end of downwind. I have never seen this before.

#3) 2nd lap around (I taxied back to the runway with Fuel boost on the whole time to try and keep pressure high). I did feel the slight feeling of drop in power for a couple seconds followed by a slight surge in power then slight loss and slight surge a few times. The data though looks pretty clean on this run.

I am now pulling the last amount of hair I have out of my head. Worried this might be a valve problem on #3.

Again, I don't feel noticeable misses on startup. It has a good rhythm to it and doesn't shake or feel like anything is off.

I am getting concerned to fly it thinking something is really wrong with the #3 cylinder and it is going to throw a rod in flight or am I just overthinking this?
Have you checked injectors? Any change on fuel burn rate? If you swapped 3 and 4, does the problem chase the swap? Injector could be fine at low power, but starting dumping fuel when pushed to full. Just a thought.

apologies if I'm repeating something.
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  #37  
Old 12-03-2020, 05:03 PM
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PerfTech PerfTech is offline
 
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Default Possible Cause?

... Try this as you lift off on second go round! Switch off your lightspeed ign.
and just see what happens, do offs and ons and see how it acts. Thanks, Allan
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  #38  
Old 12-04-2020, 08:11 AM
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Low Pass Low Pass is offline
 
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Check the ignition. Been there, done that. Symptoms appeared after engine was warm and had run a while. Also, one intake valve problem affects all 4 cylinders. Been there, done that too.
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Last edited by Low Pass : 12-04-2020 at 01:56 PM.
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