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  #1  
Old 09-20-2020, 08:35 PM
wjb's Avatar
wjb wjb is offline
 
Join Date: Nov 2012
Location: Half Moon Bay, CA
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Default Weird EGT wiggles after hot start

I've found an interesting EGT oscillation after hot start that I request the VAF brain trust to opine upon ... This shows up after a hot start during taxi. IO-360-M1B, 30 hrs TTSN, running great in all other respects. The engine broke in nicely during phase 1 and is purring along happily.

I noticed a ~10 second oscillation in EGT after a hot start at low power operations (ie, taxiing back to hangar or departure end after a fuel stop). The plot below shows it on #4, but I've also seen it on all cylinders together (#4 is the most common). This clearly doesn't seem to be the burnt exhaust valve oscillation generated by the rotator cap, but may be due to hot fuel in the spider after a heat soak.

Go fly, and this doesn't ever show up again (until a hot start + taxi ...)

What say you, VAF brain trust?

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Last edited by wjb : 09-20-2020 at 08:38 PM.
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  #2  
Old 09-21-2020, 05:57 AM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,285
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I suspect some fuel is vaporizing in the fuel lines. It’s basically normally for an injected engine. A lot of heat builds up under the cowl and fuel can start to vaporize. As soon as you push the power up for takeoff the higher flow rate and pressure solves the problem. In other words it’s normal after a hot start. Many 4 bangers won’t idle smoothly after a hot start with high OAT.
G
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Last edited by sailvi767 : 09-21-2020 at 06:00 AM.
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  #3  
Old 09-21-2020, 06:09 AM
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RV10inOz RV10inOz is offline
 
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Location: Brisbane Qld. Aust.
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Quote:
Originally Posted by sailvi767 View Post
I suspect some fuel is vaporizing in the fuel lines. Itís basically normally for an injected engine. A lot of heat builds up under the cowl and fuel can start to vaporize. As soon as you push the power up for takeoff the higher flow rate and pressure solves the problem. In other words itís normal after a hot start. Many 4 bangers wonít idle smoothly after a hot start with high OAT.
G
What he said.

Look at your fuel pressure to. Such low flow rate means boiling fuel.
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  #4  
Old 09-21-2020, 07:27 AM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
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#4 EGT fluctuation is WAY too stable of a rhythm to be boiling fuel. Looks like electrical interference to me (notice how the oscillation pattern follows the general temp pattern of all EGTs). You can even see how EGT #2 is following a similar pattern with much less severe range of oscillations. Also, boiling fuel won't drop the EGT 600-800 degrees in 2 seconds, fully recover in 6 seconds, then do it all over again. This consistently repeats, in perfect harmony, 30 times with a consistent period. Sorry, but boiling fuel doesn't have such perfectly predictable behavior.

I would be looking for spark plug wires running close to and in parallel with EGT lines. I did that on my 10 and had very similar, wildly intermittent EGT swings. Completely abated when I got separation of the wires. Though in my case, I never saw the issue at idle, like you are.

Larry
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Last edited by lr172 : 09-21-2020 at 07:52 AM.
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