High EGT on one cylinder

High EGT on one cylinder

I own a 1980 TR 182 with a carborated Lycoming 540 engine. I reciently replaced the lower plugs with A/C XL URHB32S wire plugs. Soon after this I noticed the #5 EGT was running about 100 degrees higher than the other EGT's and even higher than the TIT. The compression is 76 over 80 on that cylinder. We changed the EGT probe and the temp was still highest. I have noticed that the right side cylinders
run higher than the left side. The baffeling is new and positioned correctly. I use a JPI EDM 700 engine anilizer.
Is it possible that this could be due to fuel distribution in the manifold? Any suggestions as to where the problem a lie?

JOHN EASTON
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Re: High EGT on one cylinder

John:

It sounds like you may have a bad plug on the #5.  We find that about 2-3% of brand new plugs are bad.   harrrumph!

I'd suggest that you do an in-flight mag check and let's verify that all of the plugs are good.  If they are, you could have an induction coupling leak near the #5.

Walter

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Re: High EGT on one cylinder

Walter, I forgot to mention yhay I did an inflight mag check and it was OK. How do you go about tracing down an inductiob
leak? John

JOHN EASTON
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Re: High EGT on one cylinder

John,

Just for clarity, when you said the following, I assumed you meant the CHT's on the right side indicated higher than the CHT's on the left side?  (This makes sense considering Walter's response.)

"We changed the EGT probe and the temp was still highest. I have noticed that the right side cylinders
run higher than the left side."

It's probably a silly question, but I thought I would ask any.  I could construe the wording to mean that the EGTs associated with the cylinders on the right side indicate higher.

Also, do you have a precise flight standby vac and if so is it connected to the intake on cylinder #5?  It could be a source or an intake leak on a single cylinder.

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Re: High EGT on one cylinder

Barry, The EGT's on the right side are higher than the left side. All six CHT's are within 20 degrees of each   other in curse. My stand-by vacumn system is electric. John

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Re: High EGT on one cylinder

John, 

Here is a few other things I thought you could try without doing harm.  A&P’s please chime in if you think I’m wrong.

1) What happens if you switch the lower wire spark plug in cylinder #5 with one from another cylinder? See if it changes the EGT in #5.  That should tell us if the problem is the spark not firing properly.  If there is no change, then check the wire is good and / or try using one of the old massive plugs in the place of the wire plug in #5 and see if the EGT is still high.  If it returns to normal while using the massive plug, then there is something about having a wire plug that doesn’t necessary agree with your particular engine.  Contact the manufacturer of the spark plug and ask them if they have seen this before.

2)  How can you confirm if it’s an induction leak close to this one cylinder so that it affects only this single cylinder?  It could be the gasket on the spark plug that is leaking?  Did you notice any exhaust gas marks around it the spark plug?  Changing the sparkplug may cure the problem, so check that it was properly torqued before removing it. 

I speculate that an intake leak on one side could be the cause of one side of the engine having higher EGTs than the other due to a leaner mixture.  If differences were due to a weird f:a distribution then I would think the differences in EGTs would be a pattern more like observing differences from the farthest cylinders from the carburetor to the closest cylinders.

3)  (This one’s a guess)  You might want to try this if you can record data from you engine analyzer.  If it is a leak around the spark plug or another intake leak that only affects that single cylinder, you might confirm it by doing the following.
While at idle or low RPM, whichever is normal for shutting down the engine, slowly lean the engine until it gets rough and then finally quits.  Review the EGT data and see if the #5 cylinder leans the fastest and quits before any of the other cylinders.  I don’t know if this is possible with your engine analyzer.

Explanation:  At low RPM with the throttle retarded you draw the lowest manifold pressure which I speculate may exacerbate the leak (depending on what is leaking).  I say depending on what is leaking, because the added differential pressure may improve sealing a leaking gasket and hide the leak.  However, it does quit first, this would tend to support the intake leak.  If it doesn’t, it doesn’t rule it out for two reasons.  a) While at cruise your manifold pressure is high and with this lower differential pressure the leak may appear.  In that event, checking the torquing on closure bolts/clamps for the intake manifold may solve the problem.   b) the fuel air ratios are not that predictable in a carbureted engine so the one that quits first may just be due to that distribution and not an intake leak!

Anyway, perhaps this will give you some other ideas, hopefully it doesn’t confuse you....

Barry

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Re: High EGT on one cylinder

Barry, Thanks for the ideas; I will have a chance to check some of suggestions out later on this week and will let you know how it comes out. I have already replaced the wire plug in the #5 cylinder and it did drop the temp 10 degrees but that cylinder EGT is still much higher than the rest. John

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Re: High EGT on one cylinder

I have a C172K with Powerflow and 4 cyl EGT.

I had #4 running about 100+ deg higher than the other cylinders and chased this problem for months (I fly twice a week), even replacing the carb, mags and plugs. I had to throttle back in cruise to 2450 rpm to keep #4 under 1575 degrees or pull carb heat if it got too high.

Anyway, I heard about induction leaks so replaced the intake hoses and clamps. #4 went normal, over 125 deg less, but #3 went up over 125 deg higher than the rest. I tested and found the EGT probes were in the correct cylinders.

I had the mechanic pull the intake pipe from the #3 cylinder intake and found a lot of old gasket not scraped off. He cleaned it, put in a new gasket but #3 still ran 100+ deg over the rest.

He then again removed the intake air pipe, put the flange part on a mill and got it absolutely flat. He put in high temp gasket sealer and two gaskets. All is now fine.

I can now take it to 75% power 2600 rpm (I have Powerflow, Challenger K&N air filter and 3" repitched prop) and max forward speed of 140 mph (top of the green) during an IFR approach (lot of jet traffic) with no problems on any cylinder EGT. I land at sea level.

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