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Diagnose my engine


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Challenge question - help me diagnose my engine.

...let me start - all safe and sound uneventful landing.

Long story short - in flight today I had some significant - but not severe - roughness in flight today and a moderate/significant but not severe reduction in power.

Long story long - so I went up with a friend today. with the intent of re-calibrating my AOA indicator (alpha systems) since it had lost its preset when I had some battery adjustment which caused the AOA to loose its saved values - likely because I forgot one last button press to save values properly last time around quite some time ago.  ANYWAY the configuration involves flying at near stall speed with zero climb - i.e. a variant of slow flight.  We did this 3 separate times as we were trying to remember the buttonology.  Me flying and him pressing buttons.  It took a bit of time. 

So I had a rather low engine setting during this period at relatively low manifold setting (18'') and 2400rpm, and low fuel flow to match.  Any more than that and the nose points up quite a lot and it starts feeling more like a departure stall.  Remember I am setting my AOA and not specifically practicing slow flight.  We were at 6500.  The OAA (as the book calls the configuration) calls for lowish power (like near pattern flight settings but I did a tad below that as you see) and pull back until you stop climbing - so this is clearly a configuration that is flying at low power but behind the power curve.

Well after about 30 min of flight and almost right after the AOA setup was finished, the engine started running a tad almost inperceptably rough, and shortly thereafter, unmistakably rough.  I mean rough - not severe shaking or anything.  With some unmistakable loss of power.  We were 6 or 7 miles from the airport at 6500, so it was easy work getting home.  Nice clean landing.  Oh when it started getting rough then I was at 23'' shortly after the 3rd slow flight.  I switched tanks, richened a bit, leaned a bit, and then decided to leave the power alone since it was running and just focus on getting to the runway.  Well on final. it. actually cleaned up a bit and pretty well smoothed out and. power improved.  So I was coming hot as I was saving energy and yay for speed brakes, I easily slowed to reasonable speeds over the gate and made an absolutely normal and smooth landing using a normal amount of runway.

I did some normal 18''  run-ups and also some 22 and 23'' higher power than usual run ups and all seemed normal.  But at taxi-speed power 10'' it seemed oh so imperceptibly rougher than typical.

So she is waiting in my hangar right now for a visit from the IA.

Oh - and the critical hint - EGT 6 was very high temps.  All other EGTs were normal and even reduced in temps when 6 got hot, and all cylinders were normal cool, very cool compared to cruise since these were low power ops.

I think I either fowled a spark plug or possibly an injector.  What does Mooneyspace brain trust think?

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@aviatoreb Erik...

Your Description matches a fouled plug on that cylinder...

The fuel is only getting partially burned in the cylinder...

The rest burning in the exhaust...

Hence the elevated EGT on that cylinder...

Slow flight, and low power settings can cause the fouling... extra care in leaning probably helps to avoid the situation...

Got the JPI data?

Great download experiment to identify exactly which plug it is...

Run-up data should expose the fouled plug...

Normally Aspirated PP thoughts only, not a mechanic... :)

Best regards,

-a-

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33 minutes ago, carusoam said:

...Slow flight, and low power settings can cause the fouling... extra care in leaning probably helps to avoid the situation...

Got the JPI data?

Great download experiment to identify exactly which plug it is...Run-up data should expose the fouled plug...

Yup - just posted.  The moment the problem starts sticks out like a sore thumb, eh?I WAS trying to lean appropriately during the slow flight - as you see quite warm EGT during the middle period. when. the power was. exceedingly low - as I was leaning.  I guess it didn't work.

Yah - all bets are on a fowled plug or possibly fowled injector.  I might find nothing on visual inspection (which will happen before I fly again) since it may well already be cleared.  Which is a very unsatisfying answer.

Normally Aspirated PP thoughts only, not a mechanic... :)

 

You are so funny Anthony. Makes me laugh every time you do that.

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Just now, neilpilot said:

So you didn't try switching to a single mag?  Too bad, since that test might have revealed if it was actually a plug, and which one (it's usually, but not always, the lower plug).

However, my money is on a fouled injector.

 

I did a mag check on the ground after landing and nothing stood out by that time.  But in flight - significant roughness and loss of power - I was not sure what was going on and there was a nice runway right near by so I made a bee line for the runway - emphasis on safe landing with what working engine I had ... In any case if it was something much worse. (Still not for sure it is not something much worse) I wanted to get there without hesitation lest it get worse and I loose that opportunity.

 

 

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11 minutes ago, DXB said:

Would the higher CHT on 6 during the high EGT period make you favor an injector over a fouled plug, which should not raise CHT?

I dunno. But nothing was particularly hot at all so I am not sure.  Do you think even though everything is quite cool but CHT6 is hottest at 256 that is a sign pointing at injector?

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1 hour ago, aviatoreb said:

I dunno. But nothing was particularly hot at all so I am not sure.  Do you think even though everything is quite cool but CHT6 is hottest at 256 that is a sign pointing at injector?

Not sure - just thinking aloud. I'm assuming 6 doesn't normally run hotter at that altitude / speed/ power configuration (are there normal comparison flights to examine 6?).  It's pretty tight with the other 5 cylinder temps throughout  the recording, so I'm guessing the hotter CHT in the time frame of the high EGT is a consequence of whatever is going on.  I would not expect a fouled plug to raise CHT under any conditions.  A partly clogged injector might, depending on how lean it was running because of the clog?  I'm sure you're going to check your plugs on 6 regardless.  

Edited by DXB
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Hmmm...

Are you able to post the link from Savvy..?

This way we can really dive into the data.

Cylinder #6 really decided to play a game at the end of the flight.

Seems like a high Egt And elevated CHT to go with it...

I would expect a bad plug wouldn’t raise the CHT...

PP Making guesses based on one set of data in the pic...

Best regards,

-a-

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19 minutes ago, carusoam said:

Hmmm...

Are you able to post the link from Savvy..?

This way we can really dive into the data.

Cylinder #6 really decided to play a game at the end of the flight.

Seems like a high Egt And elevated CHT to go with it...

I would expect a bad plug wouldn’t raise the CHT...

PP Making guesses based on one set of data in the pic...

Best regards,

-a-

I don't know.  Is there a way to post? I am happy to do so if anyone knows how.

I wouldn't say that CH6 is elevated.  All CHT's were between 281 and 300 at minute 19, and CH4 was warmer at 300 followed by CHT6 at 298.  EGT

Then by minute 42:30, EGT6 was 1617 and CH6 was 256, CH4 was 226, on down to CH3 was 216.  SO elevated seems like the wrong phrase.  Cooled off but cooled off the slowest is more true.  Is this a relevant distinction?  Could it still be a bad plug or injector?  Seems like if it were something else CHT's wouldn't decrease but would increase.  CH6 decreased from 298 to 256 in 3:30 minutes, which albeit the slowest decreasing is still decreasing.

I have appt tomorrow am to look into it with ... assistance.

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Yes it is that easy... :)

we can click away getting lots of data to compare...

Whatever was going on was happening in the last few minutes...

Around 40:00 to 42:00 and on...

The EGt 6 and CHT 6 leave the other cylinders...

CHT 6 is close until this time frame... then it becomes 30°F warmer than the rest...

But it’s only a few minutes before the FF gets pulled back...

Get a close look at where the EGt6 goes funny... it seems to occur after the FF gets adjusted from about 11 to 9...

 

So if it’s a plug... should be able to be easily ascertained... using Jpi data...

if it is a fuel injector... it is showing the effect better during lower FF... (?)

 

If you get a chance... do an extended time between switch positions... and really see if there is an effect between EGTs and mags...  I don’t see anything standing out in the run-up... both mags and all EGTs are trending similarly...

Extended time... add 15 seconds if you can... it’s only a few data points if your JPI is set to the fastest cycle time... (1 or 2 seconds per data point)

 

Best regards,

-a-

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Post script.

Plugs out and injectors out- nothing found.  We collectively decided it was as already we suggested - that too much slow flight at very low power settings fouled the plugs or injectors, and it cleared out on its own.  A little cleaning them up anyway, and some high power run up to make sure everything was in order, and I flew yesterday for 30 min without a hitch a blink or a hiccup -and I flew at a good solid 72% after a full power climb just for good measure.  31'', 2300 and a bit of 75% 31'' 2400. She ran as usual.

So my fine wire plugs have about 900 hrs on them.  The AP thought the residence is getting a bit high.  How long do those last in general?  How do I know when they are done and I need new ones.

...maybe I could get someone to get some Oshkosh discount fine wires for me?  ..are they discounted at Oshkosh?

E

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1 hour ago, jetdriven said:

Tempest Fine wire plugs last 2000 hours or more. Champion Fw plugs get cracks on the insulators.. What resistance was he getting? 

Thanks for jumping in jetdriven...I am asking him right now.  Waiting for the text.

What kind of resistance should they get new - and what is a sign of aging?  Is that how one knows plugs are getting old - the resistance?  At 800 hrs in principle the might still have a lot of life in them unless they are showing high resistance.

In all likelihood it was simply the sort of flying I did that caused #6 to foul and otherwise there has never been a hiccup or a single other fouling event (incl preventive aggressive leaning on the ground).

...if I were to need new plugs - I wonder if they are cheaper in Oshkosh this week if I could get a friend to pick up a set?

Edited by aviatoreb
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1 hour ago, jetdriven said:

Tempest Fine wire plugs last 2000 hours or more. Champion Fw plugs get cracks on the insulators.. What resistance was he getting? 

Ah - just in - he was getting 800 ohms range.  in the 800's all.

He was just now telling me they are fine and was only mentioning they are a tad low compared to new, with 500 being too low and optimal being 1200-1500.

...so 800 - Im good?

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4 minutes ago, jetdriven said:

Below 4000-5000 ohms is good.  

Ok. I am just now catching up and I realize that I have been saying nonsense and I must have been misunderstanding you - and him.

800 ohms is crazy low resistance so that would be very very good?  But impossible.  And high resistance (big numbers) is bad.

Darn- so I need to start over to figure where I stand.  

 

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