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M20F Engine Stumbling and Popping at Idle


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1 hour ago, carusoam said:

So...

we have two strong contenders in the discussion...

1) a dead/dying plug...

2) an induction leak...

 

Find the dead plug using proper run-up technique. It can’t hide from the engine monitor...

Check the logs to see what plugs are in there... if Champions, read up on resistance measurements... how many hours do they have?  How football shaped is the electrode?

The other brand isn’t error free... but, its challenge is slightly different...

Often, lower spark plugs collect things like lead balls and burned oil drips... find the dead plug, pull it, take pics... clean it and take pics... measure its resistance, report back...

What plugs do you have?

PP thoughts only, not a mechanic...

Best regards,

-a-

The spark plugs are the Tempest UREM38E plugs. The hours depend on which plug, some were replaced, would have to dig through the logs. 

Plan is to run it again this evening to gather more data and upload tonight. Thanks!

 

Edited by Flyman2456
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That seems to eliminate the two inherent plug challenges...

its not Champion... rising internal resistance challenge

its not a Tempest fine wire... center electrode challenge

 

Still could be contamination of the lower plugs... lead balls or oil soaking...

Best regards,

-a-

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4 hours ago, carusoam said:

3) use caution when leaning on the ground... memory challenges and loose checklist procedures can leave the mixture out during full power T/O runs...

 

If you ground lean correctly you'll barely make it onto the runway without enriching. You shouldn't be able to get more than 2000 RPM if you've leaned correctly on the ground.

-Robert

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5 minutes ago, RobertGary1 said:

If you ground lean correctly you'll barely make it onto the runway without enriching. You shouldn't be able to get more than 2000 RPM if you've leaned correctly on the ground.

-Robert

I have learned how to turn common errors into less common errors over time...   :)

This is one reason a FF check is added early into my T/O roll... MP, RPM and FF...

FT and lean usually result in a giant stumble...

Best regards,

-a-

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Curious to see what your final outcome and resolution is on this. My new-to-me this year, 69 F model does almost exactly what you are describing every so often but it seems to only do it after she warms up. And only sporadically. Normal mag check and never skips a beat once you get some power going. In my research I had resigned myself that it might be normal IO-360 low power ground ops behavior. Warm engine, fuel injection lines on top and maybe a bit of vaporization of the fuel in the lines at low fuel flow. Just enough to make it miss or sputter every once in a while. 

However, after reading this thread, I'd like to know what you find. 

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Put this on the list of things to check....

Clean the sniffle valve to make sure it is closing properly...

if it stays stuck open, excess air can enter the system causing a lean situation... that will be more noticeable at lowest rpms...

 

Something that just came to mind...of a PP.

Best regards,

-a-

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2 minutes ago, carusoam said:

I have learned how to turn common errors into less common errors over time...   :)

This is one reason a FF check is added early into my T/O roll... MP, RPM and FF...

FT and lean usually result in a giant stumble...

Best regards,

-a-

If you are really leaned out (as you should be on the ground) and you go to FT or even mag check power, my JPI EDM-900 will light up like a Christmas tree! :o EGT will spike very very quickly when you add throttle. Ask me how I know!! 

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5 hours ago, JimB said:

If you are really leaned out (as you should be on the ground) and you go to FT or even mag check power, my JPI EDM-900 will light up like a Christmas tree! :o EGT will spike very very quickly when you add throttle. Ask me how I know!! 

I'm generally so lean that I must enrichen to taxi uphill . . . . She coughs, sputters and tries to die . . . .

Edited by Hank
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6 hours ago, RobertGary1 said:

If you ground lean correctly you'll barely make it onto the runway without enriching. You shouldn't be able to get more than 2000 RPM if you've leaned correctly on the ground.

-Robert

Egads, for taxi I lean to the point where I can't get more than 1100 rpm :blink:

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I went for a flight this evening and performed several mag checks and gami tests. 

1) Ground taxi and run-up https://www.savvyanalysis.com/flight/3465025/a8524161-baaf-4704-9792-3a6adbb677bd

2) Flight https://www.savvyanalysis.com/flight/3465026/8f5f10b1-19ed-4673-90b5-8f7fe8b72f82

3) After landing and taxi https://www.savvyanalysis.com/flight/3465028/9114a858-1249-4562-b545-c388a3fb3974

A few notes:

1)- Ground taxi and run-up: Leaned for taxi, no stumbling noted.

  -Run-up, minor stumbling, increased mixture to full rich, raised RPM to 1700, performed a mag check. Some popping/stumbling noted.

2) -Take-off: no stumbling noted.

    -Cruise: Performed a GAMI spread with Wide open throttle (WOT), 2450RPM,  with a result of 0.1 GPH spread. Then performed a mag check at 30-50 LOP. Noted right Mag was rougher than left mag.

Performed a GAMI spread with WOT-10 inches MP (~17MP) and got a GAMI spread of .4 GPH

Descent- Brought throttle to idle, no stumbling noted.

3) -After landing, leaned for taxi, lots of stumbling and popping at 1000 RPM, brought throttle lower and no stumbling noted. Brought to 1000 RPM and mixture slowly reduced and engine shut down. There was no increase in RPM when pulling mixture.

I can elaborate on any of the above if need be.

Let me know if anything stands out. Thanks in advance!

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Looking at the first set of data....

 

So at about 8:00 you increase power and rpm goes with it...

What is happening at 10:00 in the first graph?

looks like one mag was run at 10:00, the next was run near 11:30...

was one mag more rough than the other?

Looks like the one run at at 10:00 has two EGT lines that are not like the others...  something to focus on because this shouldn’t be happening...

Are you seeing this as well..?

it is nice to see four separate EGT lines that are pretty well behaved... so the JPI is working pretty well...

Best regards,

-a-

 

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The second graph...

Lots going on here...

Probably too much for what you are trying to do...

A real stable data set... has 15 or 20 steps from start to run-up to T/O, climb, cruise.... leaning in cruise... then let it stabilize....

We want to see really steady EGT data and CHT data to make observations... each time the MP changes it takes about 5minutes to get everything to equilibrate....

What did you do at minutes... 34, 35, 37, 38?  Label with L or R and B to keep things from getting more confusing...

Compare 34 and 35 EGTs to each other... I am assuming these are related. EGT 3 on one and EGT 4 on the other...

Compare 37 and 38 to each other... same assumption here...

Are you seeing a particular cylinder stand out from the rest in each set?

Mag checks ideally should look identical...

In this case it seems that one set of data is taller than the other... a signature of mag timing not being identical...  the taller the EGTs on a single mag... the later the timing is, closer to TDC...

PP thoughts only, not a mechanic...

Best regards,

-a-

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15 minutes ago, carusoam said:

Looking at the first set of data....

 

So at about 8:00 you increase power and rpm goes with it...

What is happening at 10:00 in the first graph?

looks like one mag was run at 10:00, the next was run near 11:30...

was one mag more rough than the other?

Looks like the one run at at 10:00 has two EGT lines that are not like the others...  something to focus on because this shouldn’t be happening...

Are you seeing this as well..?

it is nice to see four separate EGT lines that are pretty well behaved... so the JPI is working pretty well...

Best regards,

-a-

 

At 00:10:00 the left mag is checked then back to both at 00:11:00, then right mag at 00:12:00. No roughness with either on the ground. In the air the Right mag exhibited some roughness..

Hmm at 00:10:00 it looks like the EGT's seem to follow the same trend to me..

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Let’s talk about what you are seeing in the first graph run-up...

L and R are behaving somewhat differently...

L has some close EGT lines... R is showing four lines that are different as they are spreading out and peaking higher...

L and R should be four lines on top of each other, with the same peaks....

Best regards,

-a-

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You mentioned Gami spreads...

Another collection of valuable data...

More detail is required...

A 0.1 Gami is pretty tight...

A 0.4 Gami is pretty middle of the road...

A 1.0 Gami would be crummy...

With a 0.1 Gami you can run deep LOP, 75°+ LOP down at low altitudes... at higher altitudes deep LOP becomes more challenging...

example... my IO550 had a Gami spread of 0.1 g between the first and last to peak... at 5k’ it would lean to 90°F LOP before it just shut off...

So... if you really have a tight Gami spread... how deep LOP can you go?

The logic behind this list is trying to eliminate that thought regarding an induction leak... on a single cylinder...

Notice how the EGTs had two different high EGTs depending on the mag being used... not a constant high EGT as if extra air was entering one cylinder’s intake...

 

A leaking sniffle valve may be causing some leanness still... Hank has pointed out the expected rpm rise during lean to shutdown... that rpm rise isn’t happening...?

Another oddity being introduced is the throttle plate... for the cleanest data have the throttle wide open... under normal conditions this won’t matter very much... but for Best Gami Numbers WOT is the way to go...

I’m still leaning towards a  mag misbehaving... they don’t seem to be timed the same.... stumbles because of bad timing can be really bad... (too far before TDC...) or they could just be bad for performance... (too close to TDC)

PP thoughts only, not a mechanic... Contact Savvy to share your data for a professional review... :)

Best regards,

-a-

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What I can’t figure out... yet...

why does one cylinder peak higher on one mag and a different cylinder peak higher on the other...

If you want to pull some plugs to have a look at them...

  • 2&3 on the Lmag May be week... a week plug doesn’t burn all the fuel in the cylinder... it burns in front of the EGT sensor instead...

see We what I mean here...

Compare the circle... Lmag to the arrow Rmag....

The arrow is what they should look like... the circle identifies two EGTs that are misbehaving...

 

So if we haven’t confused the Lmag and Rmag or the CHT Numbers... it is safe to approach your mechanic to say the Lmag looks a bit funky as does the two spark plugs that are attached to it... #2 and #3...

got any new plugs to swap in? Or enough time to move these two plugs to different cylinders? This would identify if the plugs themselves are causing the challenge...

Too bad, I don’t have mechanic skills... this would be nice if I was sharing reliable information...

Best regards,

-a-

0DB9A3F4-116C-4A06-8CDC-AAD959AE12E8.jpeg

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More on timing...

i added a new line to the graph....

A Peak EGT line for running on a single mag...

If both mags are timed the same... the peaks generally occur at the same EGT...

if the timing is different... the EGT peaks and CHTs will be different...

So the added line sort of indicates the Mags being timed similarly for 6 out of 8 plugs...

The Two plugs that are misbehaving can’t be timed separately from the rest...

So chasing wires, plugs and mag parts for the two errant plugs makes some sense...

How old are the mags, wires and plugs?

How many hours on each item?

i need to get an apple pen!

Hope this was helpful for somebody, or anybody... I do this every now and then for practice... let me know if I have missed some details... it helps to know when I make mistakes... :)

Best regards,

-a-

CC7D9711-BAEA-4AB6-A4D5-16976849585A.jpeg

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Now for some awesome data....

see the EGTs in this set of graphs...

First is Rmag... EGTs are tight together... (second part of the run-up)

second is Lmag’s data... EGTs have gone somewhat awry, in a way the engine stumbling, now has a probable cause.

6/8 EGTs are near 1250°F...  2/8 have leapt to 1270 and 1290°F respectively....

The raw data  doesn’t mean very much... but the fact the two data points have leapt away from the others is very meaningful....

Now it’s Time to see a mechanic...

Double check to see if Champion plugs really aren’t in there... this behavior is typical of a plug resistance that is too high... :)

I’m Still a PP, not a mechanic...

Best regards,

-a-

-a-

7690F63A-1CE0-4E0A-A9EF-0B59C4493C2B.png

673D0004-2F19-48D4-8D15-75D47AE37298.png

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