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Deposit on plugs?


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M20C--

 

Had a bad runup on one mag a few months ago. Turned out to need a new spark plug. On runup today, same issue. I again attempted going to 2500RPM for 30 sec and run up again, smooth. I assume this is deposit on the plugs.


A few questions:

1. Best way to prevent this? I've read leaning mixture during ground operations; I already do this, but maybe not aggressively enough? How much do you lean?

2. As for "blowing deposit off" the plug (theoretically what we're doing with high RPM for short period of time, right?), what is the appropriate procedure to do this? Full rich to 2500RPM? Lean at all? For how long?

 

Thanks!!

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Brett, can you give a few more details? Type and make of plugs? (fine wire, massives, Champion, Tempest) Time on plugs? Do you know which plug is giving you problems? Sometimes the plugs are crying out for replacement by doing this, and sometimes there are other issues at play.

When I was having this problem, I would run up to high RPM and then lean to get the cylinders hot enough to see a good rise in temperature for a few seconds. My resolution was to change plugs (Champion fine wires out). I lean fairly aggressively on the ground and have not had any problems with my plugs (Tempest massives) for the last 200+ hours.

Welcome aboard!

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20 minutes ago, BrettKS said:

M20C--

 

Had a bad runup on one mag a few months ago. Turned out to need a new spark plug. On runup today, same issue. I again attempted going to 2500RPM for 30 sec and run up again, smooth. I assume this is deposit on the plugs.


A few questions:

1. Best way to prevent this? I've read leaning mixture during ground operations; I already do this, but maybe not aggressively enough? How much do you lean?

2. As for "blowing deposit off" the plug (theoretically what we're doing with high RPM for short period of time, right?), what is the appropriate procedure to do this? Full rich to 2500RPM? Lean at all? For how long?

 

Thanks!!

Engine monitor, single EGT gauge or nothing?

I don't know that I'd run as high as 2500 RPM on the ground, that's just asking to pick up debris and chipping the prop.  I'd just keep it at 1900 RPM for 20-30 seconds longer and redo the mag check.  IIRC, Lycoming says you can also lean the mixture during this extended runup, but need to watch your CHT's.

Most people here believe in leaning aggressively during taxi.  I lean to the point RPM maxes out at 1100-1200 RPM.  That's usually less than 1/4 mixture.  Will keep plugs cleaner, and you can't accidentally takeoff without full mixture.

Also, remember, you probably picked up stuff on the plugs on the way down from the last flight, since you were probably at low power during the descent as well as taxi.  Lycoming suggests running at 1800 RPM for 15-20 seconds immediately prior to shutdown to clear the plugs, but it is not clear whether there is good evidence to support this (Mike Busch suggested in a seminar this is an old wives' tale).

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- Leaning on ground is essential in my C model- sounds like you already do it. I lean as far as I can without needing to enrich when I increase power to taxi. Some folks lean further than that and must remember to enrich to taxi or they get a stumble to remind them.  My plane used to routinely fowl champion fine wire plugs when I first got it before I started leaning aggressively - fine wires are not immune from this problem. Of course that generation of Champion plugs had other problems.  I now run Tempest massives with no issue. 

- Consider whether your idle mixture is too rich and contributing to fowling on the ground - how to test for it and adjust on the C model is detailed in multiple threads here

- When fouled, I generally take it to 2000 RPM while leaving it leaned out for 15sec - I've only had one instance where this failed to clear the fouled plug.

- An engine monitor will effectively diagnose which plug it is based on which mag runs rough + which cylinder goes cold at runup.  Just know L mag on O360-A1D fires bottom #1/2 and top #3/4.   It's great info to have, particularly if clearing doesn't work and you want to pull and clean just one plug and get back in business.

- Consider cleaning, gapping, rotating your own plugs every 50 hrs or so. Resistance test at same time with a simple ammeter and visually inspect ceramic insulator for cracks.  Taking control of this part of my maintenance has left me with a smoother running engine and no fouling issues.

- An oily plug noted on one occasion doesn't mean much, but the same bottom plug appearing oily every time you pull it and being the offending plug on runup can be informative of the health of that cylinder.    

-Once the plugs are in good shape, you can do an in flight mag check in cruise with it leaned out  - the engine monitor in this condition is very sensitive to other problems in the ignition system.  Savvy offers an analysis service where you can upload the data.

 

As carusoam would note, these are tentative thoughts from a lowly PP - I am not an A&P

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Not as sophisticated as the rest of the comments, but my F needs to be leaned on the ground nearly to the point that an application of power will cause the engine to stumble.  Took a while to figure this out, but now it’s second nature.  

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3 hours ago, pilot_jb said:

Not as sophisticated as the rest of the comments, but my F needs to be leaned on the ground nearly to the point that an application of power will cause the engine to stumble.  Took a while to figure this out, but now it’s second nature.  

I lean my C aggressively enough that I needto enrichen to taxi uphill . . . Almost never foul plugs. When I do, it's 2000 RPM, leaned less than at cruise, for 60 seconds. 

Oil change time is good for checking / cleaning plugs.

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Some great comments on agressive leaning for taxi which is good advice. But for those of you that say without you experience plug fouling often - consider that is abnormal as well. With a properly set up mixture idle adjustment you shouldn't have to lean very much and shouldn't be seeing plug fouling if you don't aggressively lean. I fly right seat in a lot of Mooney's and often see some stumble at idle or hear about plug fouling and then suspect and overly rich idle mixture. So try this at shutdown to check your idle mixture. On fuel injected engines: First idle at 1000 RPM full rich for a good 30 sec to a minute to stabilize fuel flow, then use the throttle to reduce map to minimum RPM. It should be very near 700 RPM and be able to smoothly idle. We're still full rich, but next slowly lean the mixture till it dies. Before it dies, you should see an RPM rise of 20-50 RPM for most engines. RSA (for the lyc io-360) allows 20-40 RPM rise and says even 0 rise is okay but I personally find 0 too lean. But often I see engines with 100 or more rpm rise which is way too rich - no wonder these folks complained of fouling plugs, as well as inability to go full rich for landing without engine stumble etc. Adjusting it back to spec is easy for your A&P so if that's the case for your engine get it taken care of and you should also be able idle smoothly around 700 rpm.

When you do need to burn off a fouled plug for a bad mag test, as someone suggested above use 2000 rpm as the max and only in a clean area, and aggressively lean letting EGT's come up above 1400-1500F for a max of about 30 sec before CHTs get near 400F. And then go back down to a thousand rpm leaned as you may need to give it a few seconds to cool down before trying another mag check. But if it's going to clean up, that should do it, but watch temperatures while doing that.

Sent from my iPhone using Tapatalk

Edited by kortopates
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13 hours ago, kortopates said:

Some great comments on agressive leaning for taxi which is good advice. But for those of you that say without you experience plug fouling often - consider that is abnormal as well. With a properly set up mixture idle adjustment you shouldn't have to lean very much and shouldn't be seeing plug fowling if you don't agressively lean.

Thanks for the info!  I'll admit, the other reason I aggressively lean is because it seems to decrease the amount of black stuff I get under the nose...

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23 hours ago, Oldguy said:

Brett, can you give a few more details? Type and make of plugs? (fine wire, massives, Champion, Tempest) Time on plugs? Do you know which plug is giving you problems? Sometimes the plugs are crying out for replacement by doing this, and sometimes there are other issues at play.

When I was having this problem, I would run up to high RPM and then lean to get the cylinders hot enough to see a good rise in temperature for a few seconds. My resolution was to change plugs (Champion fine wires out). I lean fairly aggressively on the ground and have not had any problems with my plugs (Tempest massives) for the last 200+ hours.

Welcome aboard!

I am unsure of make/type of plugs nor which is causing problems. I'll think to check EGT on each cylinder next time to narrow it down. Thanks for the tips.

23 hours ago, jaylw314 said:

Engine monitor, single EGT gauge or nothing?

I don't know that I'd run as high as 2500 RPM on the ground, that's just asking to pick up debris and chipping the prop.  I'd just keep it at 1900 RPM for 20-30 seconds longer and redo the mag check.  IIRC, Lycoming says you can also lean the mixture during this extended runup, but need to watch your CHT's.

Most people here believe in leaning aggressively during taxi.  I lean to the point RPM maxes out at 1100-1200 RPM.  That's usually less than 1/4 mixture.  Will keep plugs cleaner, and you can't accidentally takeoff without full mixture.

Also, remember, you probably picked up stuff on the plugs on the way down from the last flight, since you were probably at low power during the descent as well as taxi.  Lycoming suggests running at 1800 RPM for 15-20 seconds immediately prior to shutdown to clear the plugs, but it is not clear whether there is good evidence to support this (Mike Busch suggested in a seminar this is an old wives' tale).

EGT gauge only. Based on what I'm reading, it's not nearly enough. I probably don't go below 3/5 mixture %.

23 hours ago, Yetti said:

Which plug on which cylinder did you replace?

Do you lean before you turn off the runway?

Do you go full rich in the landing phase?

 

1. Need to look at logs, can't remember.

2. I lean just after turning off the runway.

3. Yes, I go full rich in landing phase.

23 hours ago, DXB said:

- Leaning on ground is essential in my C model- sounds like you already do it. I lean as far as I can without needing to enrich when I increase power to taxi. Some folks lean further than that and must remember to enrich to taxi or they get a stumble to remind them.  My plane used to routinely fowl champion fine wire plugs when I first got it before I started leaning aggressively - fine wires are not immune from this problem. Of course that generation of Champion plugs had other problems.  I now run Tempest massives with no issue. 

- Consider whether your idle mixture is too rich and contributing to fowling on the ground - how to test for it and adjust on the C model is detailed in multiple threads here

- When fouled, I generally take it to 2000 RPM while leaving it leaned out for 15sec - I've only had one instance where this failed to clear the fouled plug.

- An engine monitor will effectively diagnose which plug it is based on which mag runs rough + which cylinder goes cold at runup.  Just know L mag on O360-A1D fires bottom #1/2 and top #3/4.   It's great info to have, particularly if clearing doesn't work and you want to pull and clean just one plug and get back in business.

- Consider cleaning, gapping, rotating your own plugs every 50 hrs or so. Resistance test at same time with a simple ammeter and visually inspect ceramic insulator for cracks.  Taking control of this part of my maintenance has left me with a smoother running engine and no fouling issues.

- An oily plug noted on one occasion doesn't mean much, but the same bottom plug appearing oily every time you pull it and being the offending plug on runup can be informative of the health of that cylinder.    

-Once the plugs are in good shape, you can do an in flight mag check in cruise with it leaned out  - the engine monitor in this condition is very sensitive to other problems in the ignition system.  Savvy offers an analysis service where you can upload the data.

 

As carusoam would note, these are tentative thoughts from a lowly PP - I am not an A&P

Yes, I do have cylinder temps that would help diagnose which plug I'm having trouble with. I can't recall which # was replaced, will have to check logs.

22 hours ago, pilot_jb said:

Not as sophisticated as the rest of the comments, but my F needs to be leaned on the ground nearly to the point that an application of power will cause the engine to stumble.  Took a while to figure this out, but now it’s second nature.  

Yes, I think I'm way too rich based on what I'm reading here.

18 hours ago, Hank said:

I lean my C aggressively enough that I needto enrichen to taxi uphill . . . Almost never foul plugs. When I do, it's 2000 RPM, leaned less than at cruise, for 60 seconds. 

Oil change time is good for checking / cleaning plugs.

Yeah, 2000RPM seems more reasonable than 2500RPM.

18 hours ago, Cyril Gibb said:

If you can increase the throttle during taxi without the engine stumbling, you’re way too rich.  

Thanks for all of the comments and suggestions.

16 hours ago, kortopates said:

Some great comments on agressive leaning for taxi which is good advice. But for those of you that say without you experience plug fouling often - consider that is abnormal as well. With a properly set up mixture idle adjustment you shouldn't have to lean very much and shouldn't be seeing plug fouling if you don't aggressively lean. I fly right seat in a lot of Mooney's and often see some stumble at idle or hear about plug fouling and then suspect and overly rich idle mixture. So try this at shutdown to check your idle mixture. On fuel injected engines: First idle at 1000 RPM full rich for a good 30 sec to a minute to stabilize fuel flow, then use the throttle to reduce map to minimum RPM. It should be very near 700 RPM and be able to smoothly idle. We're still full rich, but next slowly lean the mixture till it dies. Before it dies, you should see an RPM rise of 20-50 RPM for most engines. RSA (for the lyc io-360) allows 20-40 RPM rise and says even 0 rise is okay but I personally find 0 too lean. But often I see engines with 100 or more rpm rise which is way too rich - no wonder these folks complained of fouling plugs, as well as inability to go full rich for landing without engine stumble etc. Adjusting it back to spec is easy for your A&P so if that's the case for your engine get it taken care of and you should also be able idle smoothly around 700 rpm.

When you do need to burn off a fouled plug for a bad mag test, as someone suggested above use 2000 rpm as the max and only in a clean area, and aggressively lean letting EGT's come up above 1400-1500F for a max of about 30 sec before CHTs get near 400F. And then go back down to a thousand rpm leaned as you may need to give it a few seconds to cool down before trying another mag check. But if it's going to clean up, that should do it, but watch temperatures while doing that.

Sent from my iPhone using Tapatalk

 

3 hours ago, AGL Aviation said:

If you’ve already replaced the plug and the replacement is giving you problems out the gate, make sure the plugs aren’t bad right out of the box. Our shop has seen this quite a bit - more so with Champion plugs.


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Thanks

2 hours ago, jaylw314 said:

Thanks for the info!  I'll admit, the other reason I aggressively lean is because it seems to decrease the amount of black stuff I get under the nose...

:D

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