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Combustion concepts - results!

 
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recapen(at)earthlink.net
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PostPosted: Wed Dec 26, 2012 10:35 am    Post subject: Combustion concepts - results! Reply with quote

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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