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  #1  
Old 05-26-2019, 10:38 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 344
Default low EGT at idle after start

Having just installed a JPI monitor on my 0-320-h2ad (with Bendix FI), I started up today to check that all is working. I got some odd results - at idle, the EGT for #3 is MUCH lower than the other 3 cylinders. (Like less than half). As the engine was still pretty cold I don't have much info on CHT.

So, increased to about 1400 rpm. All 4 are sitting around 1100 degress CHT (I had leaned some after start). OK... back to idle. #3 went back to a quite low EGT. Repeated with the same results.

Eh? What's going on here? I doubt this is a probe problem given the temp difference changes with rpm.
Engine has about 260 hours (and 0.1 monitor time).

Some searches raised multiple theories:
low compression - was AOK at last annual, not many hours ago.
stuck/sticking valve
bad lifter or rocker on intake
bad valve spring
intake leak

Thoughts?

Thanks!
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  #2  
Old 05-27-2019, 12:47 AM
OKAV8r OKAV8r is online now
 
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Default

Intake leak is quite possible
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  #3  
Old 05-27-2019, 06:40 AM
vic syracuse vic syracuse is offline
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Default

An intake leak would cause HIGHER EGT's. Have you looked at the ignition side? Wires/plugs/gaps?
Do check the idle mixture setting on the carb as well. At idle, slowly pull mixture to cutoff and verify you get about a 50 RPM rise.

Vic
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  #4  
Old 05-27-2019, 08:46 AM
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Carl Froehlich Carl Froehlich is online now
 
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Two things to look at:
- Stuck valve
- A chunk of junk in the spider blocking the tiny idle port for that cylinder. The easiest check for this is the shot glass fuel flow test.

Carl
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  #5  
Old 05-27-2019, 09:57 AM
blaplante blaplante is offline
 
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Default Response

Note that this is fuel injection not carb. I can't figure out how the idle mixture setting on FI would cause a single cylinder mixture problem.

Regarding the spider - I would have thought that a blockage in a port on the spider would indeed cause low flow to that cylinder - which would be *worse* above idle (not better).

Thanks
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  #6  
Old 05-27-2019, 10:58 AM
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Carl Froehlich Carl Froehlich is online now
 
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Quote:
Originally Posted by blaplante View Post
Note that this is fuel injection not carb. I can't figure out how the idle mixture setting on FI would cause a single cylinder mixture problem.

Regarding the spider - I would have thought that a blockage in a port on the spider would indeed cause low flow to that cylinder - which would be *worse* above idle (not better).

Thanks
Nope - spiders do not work like that. As fuel flow goes up the diaphragm goes down exposing larger fuel ports. The idle port is small.

Do the shotglass test.

Carl
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  #7  
Old 05-27-2019, 11:05 AM
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Carl Froehlich Carl Froehlich is online now
 
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Here is the shot glass test result of a spider with a spec of junk in in.
Carl
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  #8  
Old 05-27-2019, 12:13 PM
vic syracuse vic syracuse is offline
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Quote:
Originally Posted by blaplante View Post
Note that this is fuel injection not carb. I can't figure out how the idle mixture setting on FI would cause a single cylinder mixture problem.

Regarding the spider - I would have thought that a blockage in a port on the spider would indeed cause low flow to that cylinder - which would be *worse* above idle (not better).

Thanks
My bad. I saw O-320 and assumed carb.

Definitely look at the injectors. Pressure is very low at idle.

Vic
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Kitplanes "Unairworthy" "Diagnostics" monthly feature
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  #9  
Old 05-27-2019, 06:46 PM
blaplante blaplante is offline
 
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Default And the winner is...

Fuel injection distribution spider.

Thanks! The brain trust here saved me some airplane bucks!

-Bryan
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