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1. 10:35 AM - Combustion concepts - results! (Ralph E. Capen)
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| Subject: | Combustion concepts - results! |
Just to come full circle with this...
I was seeing elevated EGT on my #4 cylinder and CHT normal...
First, I checked the spark plugs for the #4 cylinder to look for evidence of shorting
across the gap / non firing. Didn't find anything abnormal. Cleaned both
plugs and reinstalled with new gaskets.
Second, I disassembled and cleaned the fuel injector and feed tubing for the #4
cylinder. Didn't' find anything abnormal. Put everything back together and
tightened to spec.
Third, I tested the MAP sensor tubing as it is attached to the #4 primer port...found
it leaked...replaced the hoses and added some of the 37 degree gaskets
to the associated AN fittings. Both sensors attached and the entire system holds
vacuum that they would normally encounter from the intake system.
Thinking I had the 'smoking gun', I buttoned everything back up. The subsequent
test flight showed the EGT for #4 still elevated and CHT normal. The EGT graphs
showed the temp initially about 170 degrees higher than the other three (as
previously recorded 'normal) then fluctuating from 400-500 degrees - bouncing
up and down fairly erratically.
The first part of that flight made me think that I probably have another intake
leak - while the latter part made me think that I might also now have a bad EGT
sensor, sooooo...
Fourth, I removed the intake runner for that cylinder to see what I could see.
I found what appeared to be an intake gasket that wasn't deformed with a contact
compression imprint on the cylinder head side. The intake runner side was
well deformed - leading me to think the runner may not have been 'square' when
the collar bolts were initially tightened. Lucky for me, I had a spare gasket
which I installed and was careful to seat properly. The associated rubber
connecting hose appeared to be intact so it was reinstalled and tightened to spec.
Fifth, I replaced the EGT sensor for the #4 cylinder. I have had an EGT sensor
failure before and the tip was burned open with the readings being low and bouncy.
Didn't find anything abnormal on the removed sensor - but I had a fresh
one available so in it went.
Hoping since I have made two changes to the system and not being able to think
of other possibilities (not involving the cylinder) that it should be fixed -
time to close everything up and go for another test flight.
SUCCESS - between the intake runner to cylinder head gasket, the re-torquing of
the connecting hose, and the new EGT sensor, we're back to a steady-state and
can continue with the engine break-in cycle. I think the old EGT sensor will
find its way to the trash-can right next to the intake gasket - so I don't even
think of trying to re-use it.
Thanks to all for their wisdom and experience!
Ralph Capen
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