Cylinder #3

[NJMac]

I keep seeing high temps on cylinder #3 on my M20E. Had the mechanic clean the fuel injectors last year and nothing improved. Can hardly lean the mixture wanting to stay around 1400-1415 EGT, ROP. It won't run well LOP. Would you accept this as is or do I ask for some specific digging with my annual in a week?

 

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[Niko182]

If you are taking about CHTs 283 i not bad at all. if you're taking about EGTs, they don't really mean anything except where you are according to peak. Whats the gami spread?

[carusoam]

Summary.... (because Niko said it so well...)
 

To find out if it is meaningful...

We run the GAMI spread test...

So many things can affect the raw data number, they aren’t very meaningful...

Peak is where we start to see if something important is going on...

Then look at CHTs to see if there is any corroborating evidence....

For a wider view... compare various flights over time...
 

Next steps, Gami.... (the spread, not the injectors yet... )

Follow up by posting engine data on Savvy, and sharing the link here...

No, MSers don’t usually accept not being able to go LOP smoothly if they are flying behind an IO360...  Sounds like there may be room for improvement...

Doing the homework before the test, is much better than showing up to the annual il-prepared...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[Matt Ward]

Just an observation, but I’m guessing getting 24 squared at 70% should be closer to 10 gph using POH tables. Assuming you’re low - maybe 3k feet or so - does that ff work for you? Are you cruising at +13 gph to smooth out the engine? Maybe this was a climb?

[NJMac]

Just an observation, but I’m guessing getting 24 squared at 70% should be closer to 10 gph using POH tables. Assuming you’re low - maybe 3k feet or so - does that ff work for you? Are you cruising at +13 gph to smooth out the engine? Maybe this was a climb?

No climb, mid 12s gph is all I can lean it to under 5000.

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[Niko182]

Do you have gami's. Whens the last time yoy had the mags checked just in general and for timing? Sparkplugs clean?

[carusoam]

Leaning gets more challenging the higher you go...

A well balanced intake can be 90+°F LOP down low before the engine stops firing....

Challenges at 5k’ aren’t going to get better up high....

Best regards,

-a-

[NJMac]

Do you have gami's. Whens the last time yoy had the mags checked just in general and for timing? Sparkplugs clean?

No gamis, never done a gami spread. They reset my timing last year at annual. Believe they're clean. I don't wrench on the plane, never been shown how.

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[Niko182]

Id say gamis would probably be the first thing to do. Theyre relatively inexpensive. And if they end up working, they'll pay for themselves in 50 hours or less. 

[carusoam]

The Savvy site has all you need to know about performing a Gami spread test....

essentially finding peak EGT for each cylinder, and taking notes of the FF at each cylinder’s peak...

Some technique is required, but not Rocket surgery... no engineering degree required...

Patience helps... Lean slowly near peak.... for best results...

Best regards,

-a-

[Ragsf15e]

I would try the Gami spread just to see how it does but definitely not worry about the egt.  There’s nothing wrong with that egt or with “1400-1450”... why do you think there is?

If you keep the cylinders at good temps, you’re in good shape and it appears they are.

If you keep leaning, the egt a bit further, all 4 will eventually go back down... hence the “peak egt”.  There’s no Redline/limit egt number.

Finally, if you use your jpi to “lean find” (LF), and set it to LOP, you can just slowly, smoothly lean right past the peak while the jpi captures all the data.  When you get back, download it and look at the data/gami spread while at zero knots, enjoying your favorite beverage.

[Bob - S50]

First, if anything at all looks wrong to me it's your CHT's are too LOW.  In the July issue of AOPA Pilot, Mike Busch says the 'sweet spot' for CHT's is 350 to 400.  In his article he says low CHT's is an indication of low exhaust valve temperature and letting it get too low increases the likelihood of deposits on the exhaust valve stem which in turn leads to morning sickness.

As for not being able to operate LOP, have you tried it at 2600 RPM?

[Niko182]

Just now, Bob - S50 said:

First, if anything at all looks wrong to me it's your CHT's are too LOW.  In the July issue of AOPA Pilot, Mike Busch says the 'sweet spot' for CHT's is 350 to 400.  In his article he says low CHT's is an indication of low exhaust valve temperature and letting it get too low increases the likelihood of deposits on the exhaust valve stem which in turn leads to morning sickness.

As for not being able to operate LOP, have you tried it at 2600 RPM?

I think it's being run quite rich.

[NJMac]

I think it's being run quite rich.

I agree completely. Reading up on the lean find function on the EDM. May go up one evening this week just to use it. Never have.

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[NJMac]

First, if anything at all looks wrong to me it's your CHT's are too LOW.  In the July issue of AOPA Pilot, Mike Busch says the 'sweet spot' for CHT's is 350 to 400.  In his article he says low CHT's is an indication of low exhaust valve temperature and letting it get too low increases the likelihood of deposits on the exhaust valve stem which in turn leads to morning sickness.
As for not being able to operate LOP, have you tried it at 2600 RPM?

Have not tried it at 2600. You thinking that will improve this?

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[NJMac]

I would try the Gami spread just to see how it does but definitely not worry about the egt.  There’s nothing wrong with that egt or with “1400-1450”... why do you think there is?
If you keep the cylinders at good temps, you’re in good shape and it appears they are.
If you keep leaning, the egt a bit further, all 4 will eventually go back down... hence the “peak egt”.  There’s no Redline/limit egt number.
Finally, if you use your jpi to “lean find” (LF), and set it to LOP, you can just slowly, smoothly lean right past the peak while the jpi captures all the data.  When you get back, download it and look at the data/gami spread while at zero knots, enjoying your favorite beverage.

I'm looking forward to doing this. Appreciate the input from you and all so far

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[David Lloyd]

Timing would affect all cylinders, not just one.  A bad plug in #3 could make the #3 EGT higher.  Have you done a mag check in flight?  A plug might seem good at the relatively low power runup and misbehave in flight.  Check it first.  If it is a bad plug, you will feel it, hear it, and see the #3 EGT drop as others rise about 100 degrees operating on one mag. 

As already said, the EGT numbers don't mean anything by themselves.  A probe or the probe location could account for the higher indicated #3 EGT.  What is important is the relationship between all.  Climb to 8 or 9000 feet, lean in .2 GPH increments.  Wait 1 minute, write down each EGT temp. Lean, wait, write.  Repeat until all numbers are decreasing. Post your chart. 

[N231BN]

Timing would affect all cylinders, not just one.  A bad plug in #3 could make the #3 EGT higher.  Have you done a mag check in flight?  A plug might seem good at the relatively low power runup and misbehave in flight.  Check it first.  If it is a bad plug, you will feel it, hear it, and see the #3 EGT drop as others rise about 100 degrees operating on one mag.

Great advice here and it's easy to check.

I picked up a Husky for a friend about month ago. Fresh annual, mags check perfect on the ground. Had a solid miss when checking the mags in the air. It turns out someone had dropped a plug and the insulator was broken.

[Bob - S50]

11 hours ago, Niko182 said:

I think it's being run quite rich.

Which, combined with low CHT/exhaust valve temperatures will speed the rate of deposits and reduce the time before the engine develops morning sickness.

[Bob - S50]

10 hours ago, NJMac said:

 

 

Have not tried it at 2600. You thinking that will improve this?

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I'm thinking that running relatively high MP and low RPM may be making the engine somewhat unhappy to begin with.  Then when you try to run LOP, it doesn't take much for you to notice and give up trying to lean further.

Both high MP and low RPM push peak pressure (PP) closer to TDC.  During the climb you are very ROP which pushes peak PP further away from TDC.  If you level off and then try to lean slowly, the mixture will initially burn more quickly, which will push PP closer to TDC and your engine may be complaining just a bit.  You may be interpreting that as running rough.  The mixture will continue to burn more quickly until you get to peak EGT.

I was thinking that if instead of running 24"/2400 RPM, if you tried 22"/2600 RPM or even 23"/2500 RPM the engine might not complain as much and you might find you can run LOP.

[NJMac]

I'm thinking that running relatively high MP and low RPM may be making the engine somewhat unhappy to begin with.  Then when you try to run LOP, it doesn't take much for you to notice and give up trying to lean further.
Both high MP and low RPM push peak pressure (PP) closer to TDC.  During the climb you are very ROP which pushes peak PP further away from TDC.  If you level off and then try to lean slowly, the mixture will initially burn more quickly, which will push PP closer to TDC and your engine may be complaining just a bit.  You may be interpreting that as running rough.  The mixture will continue to burn more quickly until you get to peak EGT.
I was thinking that if instead of running 24"/2400 RPM, if you tried 22"/2600 RPM or even 23"/2500 RPM the engine might not complain as much and you might find you can run LOP.

I'm up for anything. Appreciate the thought. Can't wait to try some of these ideas this week. Will report back

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[NJMac]

Timing would affect all cylinders, not just one.  A bad plug in #3 could make the #3 EGT higher.  Have you done a mag check in flight?  A plug might seem good at the relatively low power runup and misbehave in flight.  Check it first.  If it is a bad plug, you will feel it, hear it, and see the #3 EGT drop as others rise about 100 degrees operating on one mag. 
As already said, the EGT numbers don't mean anything by themselves.  A probe or the probe location could account for the higher indicated #3 EGT.  What is important is the relationship between all.  Climb to 8 or 9000 feet, lean in .2 GPH increments.  Wait 1 minute, write down each EGT temp. Lean, wait, write.  Repeat until all numbers are decreasing. Post your chart. 

Will be back with the chart. Thanks

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[jaylw314]

The higher #3 EGT seems irrelevant, unless that's been a recent change.  Check the EGT sensor probe, mine partly backed out of the hole once, and needed to be resecured.

Is there a chance your fuel flow transducer has not been calibrated correctly, or that your JPI has the wrong K-factor entered for your transducer?  13.3 gph seems almost impossibly rich at 24/2400.  From my POH, best power is at 10.2 gph.  That seems like pretty much full rich, and if your motor requires full rich just to run, that seems very wrong.  It might mean you have a really weak ignition system, but I'd put more money on it being a fuel flow calibration problem.  Do you have a factory fuel flow you can cross check it with, or have you confirmed the fuel flow with your refueling?

[carusoam]

 NJ,

Try uploading your JPI data to savvy...  

As J pointed out above... 13 gph is pretty high for anyone cruising behind a four cylinder engine...

What altitude was this data taken at?
 

Best regards,

-a-

[Shiny moose]

I would start with your JPI set up, MP, % power, then K factor before all else. A few things seem off

Edited June 15, 2020 by Shiny moose