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  #11  
Old 11-27-2020, 08:31 PM
RedRaider94 RedRaider94 is offline
 
Join Date: Nov 2014
Location: Celina, Tx
Posts: 55
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Best I can recall, all fuel lines firewall forward have firesleeves installed with the only exception being the 4 stainless lines going from the fuel divider to the injectors. These are sitting just a inch or two above the heads. Are these lines likely where the vaporizing could be taking place and if so, should these have firesleeves installed over them?

I would have to get sleeves large enough to fit over the brass nuts on either end which are quite a bit larger than the lines themselves.
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  #12  
Old 11-27-2020, 10:18 PM
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rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
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Default GRT

Quote:
Originally Posted by RedRaider94 View Post
MP stays in the 27’s when it happen (RPM’s stay around 2650) so nothing noticeable with my eyes. I meant to record the takeoff in the GRT today but forgot to hit the record button. Will do that tomorrow to see if anything looks weird. If either are happening I am going to need data to really see it as it isn’t perceptible to me eyes.
Two things - I recommend recording all the time and just leaving a small USB key in there for cases like this. You can put the data on savvyaviation.com and get some interesting information.

You may also want to set the recording speed for this issue at the highest frequency, which I believe is 200 milliseconds. 1000 milliseconds (1 second) is probably not going to catch this issue.
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  #13  
Old 11-28-2020, 08:17 AM
lr172 lr172 is offline
 
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Does this happen at the moment that you shove in the throttle or does it come a bit later?

Dropping an ignition does create a distinct sound, but usually only a slight power reduction. You could intenionally drop one ignition to get a sense for the power reduction in this case to confirm or eliminate. Sounds like a fuel issue to me.

Larry
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  #14  
Old 11-28-2020, 08:18 AM
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Carl Froehlich Carl Froehlich is offline
 
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If this is a new issue, I would first suspect the Lightspeed ignition. If a coil problem (not unusual) it will show up with two EGTs (1&2 or 3&4) going a little higher.

Do the plug wire and spark plug resistance checks as well (Lightspeed install manually). High resistance in either will end up killing the associated coil.

Carl
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  #15  
Old 11-28-2020, 10:00 AM
RedRaider94 RedRaider94 is offline
 
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If itís happening on rollout I canít tell but start to feel it for sure about 500 ft AGL and then throughout my climb to pattern altitude. I changed EI plugs yesterday before I went up to recreate the issue and same thing so I know it isnít the plugs.

If the coil or wires were bad, I would think it would do it on the 1st takeoff of the day but it doesnít miss a beat.

Hoping to get up late this evening and do some recording at 2000 milliseconds to see if I can identify anything. Will try and post a picture of the results.
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  #16  
Old 11-28-2020, 10:47 AM
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rv8ch rv8ch is offline
 
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Default 200 - 5Hz

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Originally Posted by RedRaider94 View Post
...Hoping to get up late this evening and do some recording at 2000 milliseconds to see if I can identify anything. Will try and post a picture of the results.
Probably a typo, but I recommend going for 200 milliseconds (5 times per second).
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  #17  
Old 11-28-2020, 03:12 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by RedRaider94 View Post
If it’s happening on rollout I can’t tell but start to feel it for sure about 500 ft AGL and then throughout my climb to pattern altitude. I changed EI plugs yesterday before I went up to recreate the issue and same thing so I know it isn’t the plugs.

If the coil or wires were bad, I would think it would do it on the 1st takeoff of the day but it doesn’t miss a beat.

Hoping to get up late this evening and do some recording at 2000 milliseconds to see if I can identify anything. Will try and post a picture of the results.
Ignition doesn't really fit the symptoms, though failing coils often mis-behave when hot, but not when cold. My money is on the fuel getting too hot. On the ground, the F/F fuel system is heat soaking and that hot fuel gets to the post-servo, low pressure lines (where the pressure drops as does the boiling point) right after take off. This also explains why you don't get it on the first flight - no heat soak. You aren't using auto gas, are you? I suspect they have transitioned to the winter blend and it's lower vapor pressure.

Not certain on the diagnosis, but have a decent confidence that it is heat related. Problem right after a ground-based, heat soak and abates 30 seconds later when things cool down due to increased airflow. boiling fuel can create the hiccup symptom you describe, when it is limited in nature.

Larry
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Last edited by lr172 : 11-28-2020 at 03:19 PM.
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  #18  
Old 11-28-2020, 04:47 PM
NewbRVator NewbRVator is offline
 
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and on that plane they had a miss....

EI EI - O
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  #19  
Old 12-01-2020, 06:15 AM
RedRaider94 RedRaider94 is offline
 
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I was able to get up and do some recording although I forgot to change the settings to 200 MS - this is recording at 1000MS or every second. It is still a bit interesting and my initial thought that the tach wasn't changing on the second flight isn't true.

1st picture is the 1st takeoff. Top graph is EGT and Fuel Pressure. Bottom graph is CHT and Fuel Flow. FP is running between 27 and 29 which it always has and I think is normal. EGT's seem to be extremely consistent. I don't see anything that jumps off the page as abnormal here.

2nd picture is the 2nd takeoff. Same graphs but the only thing that jumps out is how much more erratic the tach is. It's not crazy swings but a high of 2623 down to 2587 but definitely not smooth like the first takeoff.

It's never a situation where i feel like the engine is going to quit but I can feel the back and forth of power changes in my body enough to feel that something is going on.

Any thoughts on these or what it could be? Could it be something with the Constant Speed prop or governor even (I have a slight leak on one side where the base of the whirlwind prop connects to the hub - there is a little grease coming from the seal).

I am just at a loss.....
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  #20  
Old 12-01-2020, 07:59 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by RedRaider94 View Post
I was able to get up and do some recording although I forgot to change the settings to 200 MS - this is recording at 1000MS or every second. It is still a bit interesting and my initial thought that the tach wasn't changing on the second flight isn't true.

1st picture is the 1st takeoff. Top graph is EGT and Fuel Pressure. Bottom graph is CHT and Fuel Flow. FP is running between 27 and 29 which it always has and I think is normal. EGT's seem to be extremely consistent. I don't see anything that jumps off the page as abnormal here.

2nd picture is the 2nd takeoff. Same graphs but the only thing that jumps out is how much more erratic the tach is. It's not crazy swings but a high of 2623 down to 2587 but definitely not smooth like the first takeoff.

It's never a situation where i feel like the engine is going to quit but I can feel the back and forth of power changes in my body enough to feel that something is going on.

Any thoughts on these or what it could be? Could it be something with the Constant Speed prop or governor even (I have a slight leak on one side where the base of the whirlwind prop connects to the hub - there is a little grease coming from the seal).

I am just at a loss.....
Seems pretty improbable that the governor would work unreliably in ONLY the very limited situations that you outlined in your first post. I would expect fuel boiling in the low pressure lines could easily cause the tach variations seen, as different cylinders see rapid swings across the mixture range, including too rich to fire and too lean to fire. While a 1 PSI difference is too small to be meaningful, changes in FP could point to fuel boiling as well. Would be wise to watch for consistency in FP reduction when symptoms occur. Notice in your charts that the 1 Psi reduction only occurs during the period of unstable RPM; That is a clue. Vapor lock (also boiling fuel) often results in lower FP.

Larry
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Last edited by lr172 : 12-01-2020 at 08:03 AM.
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