adverseyaw

IO-360 misfires at idle and low MP

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9 hours ago, KSMooniac said:

Who serviced the magneto?

I don't know. The guy I bought the plane from had trouble with the overhauled servo and sent it out for repair, but I'm missing that document. It may need to go out again. (I would like to pinpoint the issue before sending the mag out, but it's certainly a possibility.)

8 hours ago, carusoam said:

Looking at the rpm line...

1,000 to 1700 a few times... what is that? Or what is causing that?

If the engine is warm and running steady at idle for a minute....the ignition skips?

Got any data during that time?

if something skips, the EGT usually catches it.

It will be subtle, and can be masked by other things like moving the throttle around.

It may take some additional effort to catch a good data set that doesn’t Accidently mask what you are looking for.

Best regards,

-a-

The 1000-1700 was me running the engine up. Any idle time in the trace is time when it was skipping. (In the entire trace I probably had 5 solid minutes of idling.)

8 hours ago, KSMooniac said:

I can't tell from my phone, but if your data recording interval is set for 6 seconds it might not catch your troubles...that is worth checking and correcting.

Good point. I haven't run across the 6/1 second setting in my EDM 830 but will look again and see what I can capture.

6 hours ago, teejayevans said:

Since this is a relatively new engine, check everything is tight: fuel injectors, intake tubes, ignition wires...

Will do. We've leak-checked most if it.

6 hours ago, kortopates said:

No signs of misfire in the data, but the 6 sec default sampling rate is too slow to give much chance of seeing any. The sampling rate needs to be updated to its fastest rate of 1-2 sec to provide diagnostic value. Ground runs aren't very informative but we should be able to get some better data by isolating the mags for a good 30 sec each and see if that shows any misfire. But nothing in this data points at ignition yet; nor is it conclusive to eliminate it.

Its kinda hard to overlook EGT4 is cold. We know the cyl isn't really dead because of CHT4 but we have nothing to detect a mixture or ignition issue without EGT.

Good points -- will check into the 1-second setting and will continue to plug away at the EGT4.

2 hours ago, jetdriven said:

If your engine is in fact the A3B6D, then it’s not approved for 20 degrees of timing.  This is widely-known information. 

Interesting. Will look into this.

 

Thanks all!

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Is your engine "loping"?

http://www.donmaxwell.com/publications/MAPA_TEXT/External_Hoses/External_Hoses_Tubes.htm

"Lycoming powered, fuel injected Mooney’s, share a distinctive, “loping” sound at low power settings during taxi and idle operation. The loping sound is caused by system leakage at the induction drain valve. A small amount of “lope” is normal. Excessive “lope” can be cured by removing the drain valve hose at the drain fitting and spraying the inside of the fitting with Tri-flow, corrosion X or solvent. Fuel dye and oil cause the ball to stick and not seal properly causing rough low rpm engine operation."

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i found a replacement sniffle valve from airflow performance.  also, you can't tell if the intake tube gaskets at the head are leaking. I've changed all mine, they're a dollar each and two bolts to change.  I also coated them with permatex aviation sealer.

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10 hours ago, adverseyaw said:

Went to 20 BTDC per Lycoming SB for reducing CHTs.

Those are good suggestions. I actually don't know what plugs are on the plane. I'll check soon. Thanks!

Spend the extra money on Tempest Iridium Fine Wire plugs.  No exceptions.

Steve

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Some summarizing of thoughts.....

Fire...

Any spark plug info available?

If AY has the Champion plugs, with the ever increasing resistance...  This could be a cause of a dying plug.

 

Air...

Excess air can be leaking in causing fuel ratios to become burning challenges...

Sniffle valve and intake seals, air leaking into the fuel system... (blue stains anywhere like the selector valve?)

 

Fuel...

Flow divider issues.  How long since OH, anything on the fuel screen?

 

Data collection...

Get the JPI set on the fastest data collection speed possible.  Older JPIs may only go to 2 seconds, newer are 1 second(?)

Get the missing EGT operating. What killed the sensor may be related to the problem. The sensors live in a crummy environment.  Excessive heat and exhaust chemistry can be a challenge to their metal.  TITs have this as a common challenge.  EGTs not so much...

 

Procedure...

There is a procedure outlined on the Savvy site to best collect data, I believe... 

When performing the run-up it uses an extended time on each single mag test to allow for the usual EGT rise that comes with the single mag operation.  Back to both for the EGTs to return to the lower position...

 

The engine monitor is the best tool we have for diagnosing the cause of some pretty weird engine characteristics...

The log books is a pretty good tool to find out when something has been changed, OH’d or neglected....

 

Best regards,

-a-

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Since the symptoms are at low power and idle,  be sure to test IDLE Mixture by idling at minimum RPM and slowly leaning till the engine dies. You should see a 25-50 rpm rise before it dies - see what you get.

Checking for the sniffle valve is another good idea given the idle/low rpm symptoms.

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Mine does the occasional miss (lope, whatever) during idle sometimes as well.   As far as I've been able to determine (which seems to be being echoed here) is that this is pretty common and isn't really an issue.   I've heard and do hear lots of other airplanes do this as well.

FWIW, I have fine wire plugs in the bottom and it still does this sometimes.   Probably the drain/sniffle valve thing.

 

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2 hours ago, mooniac15u said:

Is your engine "loping"?

http://www.donmaxwell.com/publications/MAPA_TEXT/External_Hoses/External_Hoses_Tubes.htm

"Lycoming powered, fuel injected Mooney’s, share a distinctive, “loping” sound at low power settings during taxi and idle operation. The loping sound is caused by system leakage at the induction drain valve. A small amount of “lope” is normal. Excessive “lope” can be cured by removing the drain valve hose at the drain fitting and spraying the inside of the fitting with Tri-flow, corrosion X or solvent. Fuel dye and oil cause the ball to stick and not seal properly causing rough low rpm engine operation."

Yes! This is very similar to what I'm experiencing. Definitely the first thing I'll check. We haven't cleaned out that valve yet.

2 hours ago, jetdriven said:

i found a replacement sniffle valve from airflow performance.  also, you can't tell if the intake tube gaskets at the head are leaking. I've changed all mine, they're a dollar each and two bolts to change.  I also coated them with permatex aviation sealer.

Will try the sniffle valve and will look at the induction gaskets too. We pressurized the intake and didn't find issues, so I'm not certain it will be a problem, but good to know.

1 hour ago, StevenL757 said:

Spend the extra money on Tempest Iridium Fine Wire plugs.  No exceptions.

;-)

1 hour ago, carusoam said:

Some summarizing of thoughts.....

Fire...

Any spark plug info available?

If AY has the Champion plugs, with the ever increasing resistance...  This could be a cause of a dying plug.

 

Air...

Excess air can be leaking in causing fuel ratios to become burning challenges...

Sniffle valve and intake seals, air leaking into the fuel system... (blue stains anywhere like the selector valve?)

 

Fuel...

Flow divider issues.  How long since OH, anything on the fuel screen?

 

Data collection...Def

Get the JPI set on the fastest data collection speed possible.  Older JPIs may only go to 2 seconds, newer are 1 second(?)

Get the missing EGT operating. What killed the sensor may be related to the problem. The sensors live in a crummy environment.  Excessive heat and exhaust chemistry can be a challenge to their metal.  TITs have this as a common challenge.  EGTs not so much...

 

Procedure...

There is a procedure outlined on the Savvy site to best collect data, I believe... 

When performing the run-up it uses an extended time on each single mag test to allow for the usual EGT rise that comes with the single mag operation.  Back to both for the EGTs to return to the lower position...

 

The engine monitor is the best tool we have for diagnosing the cause of some pretty weird engine characteristics...

The log books is a pretty good tool to find out when something has been changed, OH’d or neglected....

Plugs: will check those next. Not sure what's in there but will probably lose Champions if I find them in there.

Air: sniffle valve is the best bet so far. Otherwise no leaks we've been able to find (nor staining -- my A&P has been pretty diligent about that since we cleaned the fuel system).

EGT: the probe is in good shape, as it reads fine when we swap connections with another cylinder. The problem is in the line or a connector upstream of the wire bundle. Still working on tracking that down.

Runup: yep, I do the EGT check for mags.

1 hour ago, kortopates said:

Since the symptoms are at low power and idle,  be sure to test IDLE Mixture by idling at minimum RPM and slowly leaning till the engine dies. You should see a 25-50 rpm rise before it dies - see what you get.

Checking for the sniffle valve is another good idea given the idle/low rpm symptoms.

Good suggestion, my A&P thought the same thing and checked this twice after the servo went back into the plane. We had it even at peak RPM at idle cutoff.

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13 hours ago, adverseyaw said:

Hi everyone, I'm trying to track down an occasional stumble I'm seeing at idle and through the bottom half of the power band. The engine, an IO-360-A3B6D in an M20J, runs well at full power.

Symptoms: every few seconds, a cylinder will fail to fire (or fires softly). The engine doesn't afterfire/backfire.

 

In trying to track this down, I had some fuel injectors get clogged due to debris in the fuel bladders. That work is done but the misfire remains.

So far I've:

  • Cleaned or replaced pretty much all of the fuel system (bladders, boost pump, mechanical pump, fuel servo, flow divider, all fuel injectors, all screens). It's clean now, no debris.
  • Pressurized the induction system, no leaks
  • Timed the engine to 20 BTDC
  • Pulled the plugs a few times, they're clear (not sure if my A&P gapped them)
  • Done about 20 runups with pretty much every combination of MP, mixture, and mags. So far, no clear culprit. It misfires at pretty much all mixture and mag settings, and all MP below about 20".

In maybe 10% of the runups I do, it will run like a top (no stumbles!) for a few minutes. So I know it's possible for it to idle cleanly.

This engine has less than 100 hours on it since overhaul so infant mortality of some part or another may be a factor.

Any ideas where to go from here? Thanks much

Have you looked at fuel pressure?  It is possible at idle the air flow in the cowl is not consistent and the metal lines that contain fuel could be heating the fuel to much and causing vapor bubbles.  It is usually because the lines are not run correctly.  This would fit the profile that you are describing that after running (engine is getting hot)  you have subtle misfires.  change RPMs cool engine down (lines get cool gas cools) less vapor less misfire.  Just a suggestion and maybe I missed the point.  

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Have you adjusted your mixture while idling? Move it all the way from full rich to idle cutoff and see if it improves anywhere in there. It may be that your idle mixture is way off.

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The flow divider is instermental in smooth idling. Take the plunger out and inspect it to see if there is any crud in it and make sure it smoothly slides up and down in its bore. Make sure the diaphagram is centered and not binding. With the plunger out you can blow compressed air through the injector lines to blow any crud out of your injector lines and divider.

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3 hours ago, Dream to fly said:

Have you looked at fuel pressure?  It is possible at idle the air flow in the cowl is not consistent and the metal lines that contain fuel could be heating the fuel to much and causing vapor bubbles.  It is usually because the lines are not run correctly.  This would fit the profile that you are describing that after running (engine is getting hot)  you have subtle misfires.  change RPMs cool engine down (lines get cool gas cools) less vapor less misfire.  Just a suggestion and maybe I missed the point.  

Good idea. The gauge reads well into the green and the problem is present with the boost pump running.

1 hour ago, N201MKTurbo said:

Have you adjusted your mixture while idling? Move it all the way from full rich to idle cutoff and see if it improves anywhere in there. It may be that your idle mixture is way off.

Yep, it's there at all mixture settings. :-/

1 hour ago, N201MKTurbo said:

The flow divider is instermental in smooth idling. Take the plunger out and inspect it to see if there is any crud in it and make sure it smoothly slides up and down in its bore. Make sure the diaphagram is centered and not binding. With the plunger out you can blow compressed air through the injector lines to blow any crud out of your injector lines and divider.

I had the flow divider cleaned, reassembled, and bench tested as part of cleaning the debris out of the fuel system. The problem was present before and after the cleaning, unfortunately.

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Well, isn't that strange. We are grasping at straws at this point. I know that an IO-360 can be made to idle very smooth and slow. 

Perhapse you have bad condensers? Have you done a mag check while it is misbehaving?

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2 minutes ago, N201MKTurbo said:

Well, isn't that strange. We are grasping at straws at this point. I know that an IO-360 can be made to idle very smooth and slow. 

Perhapse you have bad condensers? Have you done a mag check while it is misbehaving?

I think I've got enough to go on at this point. Checking the sniffle valve and sanity-checking the plugs is a good start.

Done lots of runups on one mag at a time, no change so far (RPM drop, EGT rise, but no change in misfiring). Haven't looked at condensors, but will see what I can do there.

These are all great ideas. Essentially we're eliminating variables in each system: fuel, air, spark. Getting your input helps me find new variables I may have overlooked, like the sniffle valve, which could read fine during a pressure test but could open after it gets jostled by a bit of extra fuel.

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4 minutes ago, adverseyaw said:

I think I've got enough to go on at this point. Checking the sniffle valve and sanity-checking the plugs is a good start.

Done lots of runups on one mag at a time, no change so far (RPM drop, EGT rise, but no change in misfiring). Haven't looked at condensors, but will see what I can do there.

These are all great ideas. Essentially we're eliminating variables in each system: fuel, air, spark. Getting your input helps me find new variables I may have overlooked, like the sniffle valve, which could read fine during a pressure test but could open after it gets jostled by a bit of extra fuel.

Good luck,

I can't wait to find out what resolves it.

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Time to find the Champion label on the plugs... take pics of the lower plugs to see what is growing on them. If it has a lot of oil on one, that would be a sign...

Or changing to Tempest fine wires because they are preferred by many...

Have you done the test of the mixture cut-off?  When you pull the mixture out, you should get an rpm rise... before it cuts...

Somebody recently posted a pic of the mixture hardware, the stop was missing at the engine end of the control... recently OH’d engine... pics were bright and shiny...

Keep working on the missing EGT.  That shouldn’t be too hard to find a solution for that.

I forgot, did we discuss compressions..? If compression is missing on one cylinder, there is going to be some skipping....  probably more at low rpm and low power...

PP thoughts and guess only, not a mechanic.

Best regards,

-a-

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Cracked exhaust valve guide. Symptoms started like that twice and eventually the valve guide failed. Both times when power was pulled back for descent and approach.You can fell the shudder in your butt before it lets loose.

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Cracked exhaust valve guide. Symptoms started like that twice and eventually the valve guide failed. Both times when power was pulled back for descent and approach.You can fell the shudder in your butt before it lets loose.

I’m curious, how many hours did you have at the time of failure?

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Just a thought that has been mentioned before, leaking fuel strainer shaft O ring allowing air into the fuel system?  Squirt some thick oil down the strainer shaft while it’s running to act a seal.

Clarence

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I could have missed it but, maybe something got screwed up in the mag at overhaul? Pull them and IRAN them? Saw it listed before, but Champion plugs have caused this before. Maybe a plug wire arching? Replace plug wires if they are borderline.

My bet is somthing in the mag or a improper rebuild. Grease or some foreign object shorting out.


Sent from my iPhone using Tapatalk Pro

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How are your hot starts?  That can give a lot of information about how well the mags are doing.  

Backfiring on start or during idle?  

Morning sickness yes or no?

 

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On 4/13/2018 at 2:52 PM, copierdynamics said:

Cracked exhaust valve guide. Symptoms started like that twice and eventually the valve guide failed. Both times when power was pulled back for descent and approach.You can fell the shudder in your butt before it lets loose.

Interesting. This engine has only 50 hours on it but getting extra air into the cylinder would do this.

On 4/13/2018 at 6:58 PM, M20Doc said:

Just a thought that has been mentioned before, leaking fuel strainer shaft O ring allowing air into the fuel system?  Squirt some thick oil down the strainer shaft while it’s running to act a seal.

Good idea, will check.

On 4/13/2018 at 10:58 PM, aaronk25 said:

I could have missed it but, maybe something got screwed up in the mag at overhaul? Pull them and IRAN them? Saw it listed before, but Champion plugs have caused this before. Maybe a plug wire arching? Replace plug wires if they are borderline.

My bet is somthing in the mag or a improper rebuild. Grease or some foreign object shorting out.

Interesting. The mags were overhauled 50 hours ago, but something was faulty with them causing no ability to start. The prior owner had them repaired right before I bought the plane. Could be a lingering issue with the mags.

On 4/14/2018 at 7:44 AM, bradp said:

How are your hot starts?  That can give a lot of information about how well the mags are doing.  

Backfiring on start or during idle?  

Morning sickness yes or no?

No problem with hot starts, but there is some occasional afterfiring at idle.

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An overall update:

I stuffed a bolt into the sniffle drain valve tube and ziptie'd it there. Ran the engine up but still misses at idle. No change.

The plugs are Champion RHM-38S fine wires. My A&P pulled them a few weeks ago and said they were all clean. I'll check the resistance on them soon.

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replace the intake gaskets. you cant accurately determine if they are leaking in place, and it can be a huge leak. use permatex aviation sealer on them. 

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