CHT issue on IO-550-G

[rbharvey]

Posted on AOPA, but hope someone here has good ideas of what to do next

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Let me start off that I DONT have an engine analyzer on this aircraft, wish I did to help solve this one.

#2 Cylinder seems to be going off line with erratic CHT (it is the only probed cyl) indications, starts off solid in the climb out (usually), then seems to start going erratic with +/- 20 degree swings, and the EGT drops as the CHT goes low, climbs as CHT returns, making me rule out bad probe. Cylinder will sometimes just go away with temps staying in the 180-200 degree range with EGT dropping by about 50 degress form orig stabilized value. EGT is provided at the collector for 2,4,6. No going lean condition seen with a spike in EGT temp before going off line so dont think it is a fuel system/injector problem.

Plugs were cleaned and gapped, and compression is in 50s, low but not too low for TCM. Rest of cylinders in mid 60s, to low 70s. Oil consumption about a quart/4 hours, again within specs but obviously rings leaking. Has been this way since I have owned for last 150 hours and prior to this problem. Next place to look? New plugs, MAg check, replace plug leads? help!!

[Brooks]

you did not mention if the engine sounds different/ rough or if you are having any rpm fluctuatuins.  i would suspect (although not an expert) that if mechanical/ fuel issues were causing this you would have noticed significant changes in engine sound/ performance ect.  maybey someone else will second this idea but it sounds to me like you may have a loose/intermintent ground or some other power/instrument issue, causing fluctuations in your readings.  i am curious what you mean by "off line" and how you are determining that it is only cylindger #2 or did i misunderstand.  just food for thought. 

[rbharvey]

I think I can hear the engine kind of produce a 'cleaner' sound when the CHT goes back to norm but hard to tell at 2500-2700RPM, pretty loud in the cabin. I dont see any RPM fluctuations (which I think a governor would mask very well anyway). I know it is #2 two, cause that is where the CHT probe is located. It is also the low compression cylinder of the bunch too, again down in the 50s

[TurboExec]

if you had a cylinder going dead you would be able to feel the vibration.

How did the plugs look before they were cleaned?  How much time is on the engine, cylinders?

Your probe might be failing, I've seen this kind of fluctuation before but not at the same time with both the EGT and CHT...

[rbharvey]

Th engine has about 980 hours, I have put the last 150 on it. Original cylinders from new. Plugs were a little dirty, but not bad, no cylinder stood out from others.

[rbharvey]

I am going to attack this as an electrical problem, and it does seem to be something common between the two guages,,,anybody know where the CHT and EGT share a ground ???? You would save me a lot of AMUs...thanks :-)

[Brooks]

if you can find someone with a service manual for your specific model their are schematics in the back.. i know that their are some people with the "money memory stick" that they gave out a couple of years back.  i have the one for a 231 but if you have a io-550-g i assume you dont have a m/20-k.  (i could not find a model/year note in your signature or profile).  if i can help with the info i do have i will be happy to do so.  good luck with getting this resoloved quick sans amu's

[rbharvey]

It is a 2000 Ovation2 M20R Thanks!

[rbharvey]

This has magically just fixed itself for the last 10 hours or so....who knows... but I would put it squarely in the electrical/grounding issue camp.

[triple8s]

I hope you dont think I am butting in here but I'd rather butt in and risk you're ill will towards me than to have you suffer the fate of my friend. The friend I speak of had some come and go EGT & CHTproblems with his lancair legacy w/ Supercharged IO/550 Connie. I suggested he get an engine analyzer, well, he put it off and we never thought anymore of it, then back in the summer he lost a cylinder due to lean out and it wiped the entire engine because of the aluminum spray blown into the crankcase. Several months and 50,000 $ later he is back in the air but he was just lucky he was close to our airport when it was so close to letting go. I would strongly advise of getting some type of analyzer it may save lots of money down the road, you may even save more than money. My friend Tom says he wished he'd spent the 1800$ for the analyzer instead of the engine O/H.  

                                                      Good Luck,

                                                                              Mike    KIA6

[Cruiser]

Quote: triple8s

I hope you dont think I am butting in here but I'd rather butt in and risk you're ill will towards me than to have you suffer the fate of my friend. The friend I speak of had some come and go EGT & CHTproblems with his lancair legacy w/ Supercharged IO/550 Connie. I suggested he get an engine analyzer, well, he put it off and we never thought anymore of it, then back in the summer he lost a cylinder due to lean out and it wiped the entire engine because of the aluminum spray blown into the crankcase. Several months and 50,000 $ later he is back in the air but he was just lucky he was close to our airport when it was so close to letting go. I would strongly advise of getting some type of analyzer it may save lots of money down the road, you may even save more than money. My friend Tom says he wished he'd spent the 1800$ for the analyzer instead of the engine O/H.  

                                                      Good Luck,

                                                                              Mike    KIA6

[Greg_D]

I'd like to know what "lean out" is and how you loose a cylinder because of it.

[triple8s]

On the 550 we pulled the cylinders off and one of them had a hole burned or melted, what ever you would like to call it, at the edge of the piston and down the side of the piston. The cause of this according to the mechanic was a faulty injector that caused an uneven fuel distribution and evidently one of the cylinders didnt recieve as much fuel as the others. As the engine was disassembled further molten aluminum balls were found through out the crankcase, I had a graph that shows the relationships of the temp curve, power curve, air density and the mixture ranges where detonation begins. All these things contribute to piston/cylinder failure. Cant seem to find the graph I have it on here somewhere. I did find a graph in the UGB-16 manual and according to E.I. this is what their manual says:  The following is a list of some of the problems reported from excessive EGT's and/or CHT's

*  Sticky valves due to excessive heat, causing oil to bake on to the valve stems.

*  Burnt exhast valves caused by excessive heat and /or sticky valves.

*  Extensive exhaust valve guide wear due to heat.

*  Cracks and heat damage to the ring lands caused by detonation.

Anyhow, excess heat and detonation are things I prefer to avoid even if I do use more fuel. Dont get me wrong LOP operating if done properly is more efficient, however it must be done properly and I believe there isnt as much room for error as being ROP, so, I'll buy the fuel. Thats just me.

[Greg_D]

Not only is LOP a more efficient way to run your engine, it's also a lot easier on it to boot. I'd bet you aren't running your engine rich enough if you are running your ROP.  If you're following the manufacturer's recomendations for ROP ops, you're definitely not rich enough.

[rbharvey]

The answer to this mystery was discovered during the annual for all who may come across, some chaffed wires on the EGT probe