Fouled or Dirty Plugs

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Therookguy

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Therookguy
My engine, a lycoming O-540, is running a bit rough around ~1700 RPM. I've had this issue before and MX replaced all 12 spark plugs and everything was better. This time around it seems a bit worse and the mag checks show a drop of 175-200 RPM. On both the left and right mags it runs a bit rough, which I understand is normal and this is what it has always done, but the large rpm drop is new.

At idle I can't really tell of any issues and it's a tiny bit bumpy at full throttle, but if I take my headset off I don't hear any alarming sounds or loss of power.

The issue is when I pull the power back for approach / final it sounds a little bit off and runs a bit rough, especially around 1700 rpm.

My understanding is this is likely the spark plugs getting fouled. Usually the right mag selection drops more than the left mag. I don't want to pay $700 for all my spark plugs to get replaced. I read online that I can just do a high power run up around ~2000 RPM then lean to 50 RPM LOP for a few minutes to clear it up. Is this likely to work or just make things worse?

Here's the article I read:
https://pilotworkshop.com/tips/clearing_fouled_plug/
 
The lean run-up is SOP when there are symptoms to support doing it. It won't hurt to try. If it works? It may be time to review your leaning habits.
 
Therookguy said:
On both the left and right mags it runs a bit rough, which I understand is normal
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That’s not normal. It should still run smoothly on both independent mags.

The lean run-up is also something that should’ve been taught during primary training, rather than something learned from online reading. There’s no reason it should make things worse and it’s worth a try. Simply run it up to 2000-2200 RPM, lean til RPM peaks out. EGT’s will get pretty hot and then flip the ignition to the fouling side and let it run like that for 30 seconds or so. Bring mixture and power back to the original run-up setting and then try the mag check again.
 
Maybe pull them out one at a time to inspect? Check condition of ceramic and gap?

The work Bonanza had a similar occurrence. 2 of the twelve had damage to the ceramic. And a few were off with the gap.

Once those were addressed, it has been been flying with zero problems.
 
Just tossing out some guesses.......How many hours since your mags have been inspected? might be something going on in there.

granted I have a different engine than you, but If I don't clean/gap/rotate my plugs every 50 hrs I get a good amount of lead fouling. I lean a lot but still get a good amount of build up.
 
My O-540 will foul the plugs pretty quickly if I don't lean pretty aggressively on the ground. As soon as it starts I lean and soon after landing as well. I used to have issues on mag checks during run-up till I started that practice. My CFI taught me the lean run-up. Similar to the article but for 1 min. That took care of the fouling before I started to lean during taxi.
 
What airplane is it in? Some O-540s had the HA-6 carb that ran really rich at full rich, and that's the way Lycoming wanted it, according to Precision Airmotive when I called them about it. Like StewartB says, lean it in the runup. You might have to lean it in the pattern and on approach, too, especially with carb heat on.

Check your POH on it. It might answer your questions.
 
A few things to consider..
When were the plugs last replaced?
What brand pugs were used?
The older style Champions were notorious for having excessive resistance. This causes a number of bad things, including rough mag drops. The newer style Champion's are not having resistance issues but are beginning to have nose ceramic cracking. One of the leading mag OH shops are advising their customers to steer clear until the latest problem is resolved.
Slotted screw resistor = old style. Sold = new.

Remove the plugs regardless. Put them in a trey to keep up with the location they came from.
Clean, gap and test.
Two tests are required. Electrical (bomb test) and resistance test.
Resistance should not be in excess of 5K ohms.
If everything tests good, clean the threads with a wire wheel, rotate the plugs (see attachment), apply proper anti seize, reinstall with new gaskets, torque to 35 ft lbs.
Remember, most mechanics are not checking resistance. Even though there’s a ton of evidence that suggest it’s needed, and the manual says to do it.
Remember, A spark plug with excessive resistance will still test good on a traditional bomb tester.

I just happened to be in the manual today. Here’s a snippet from my IO540 maintenance manual regarding spark plug cleaning.
b. Clean the spark plug as required, removing carbon and foreign deposits.
c. Test the spark plug both electrically and for resistance.
 

Attachments

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My take is mag issues develop in flight but do not manifest themself until the next run- up. That is often the next flight .

There is a Lycoming SI developed for the O-235 L2C and past practice of the Military and Airlines for a Post Flight Run-up.Why would you ever want to put an aircraft away w/o knowing the Ignition System is likely ready for the next flight.
In addition; it’s easier to burn off contaminants with a HOT engine.
 
I found this recently. A lead terminal split open. It was caused by a plug that had high resistance.


87C9B389-70F0-4024-A2E7-ACE8F6DF3BD5.png
 
8FC36A05-0CC3-476C-875C-9D3AEE2A165E.jpeg I have 2 sets of plugs and rotate them in and out of the motor. After I clean and gap em I keep them fresh in the refrigerator until I need em.lol

Where do you keep your plugs?
 
RyanB said:
That’s not normal. It should still run smoothly on both independent mags.

The lean run-up is also something that should’ve been taught during primary training, rather than something learned from online reading. There’s no reason it should make things worse and it’s worth a try. Simply run it up to 2000-2200 RPM, lean til RPM peaks out. EGT’s will get pretty hot and then flip the ignition to the fouling side and let it run like that for 30 seconds or so. Bring mixture and power back to the original run-up setting and then try the mag check again.
Click to expand...
What’s the benefit in running on one mag during a lean run up to clean the plugs?
 
First, the mag drop is unacceptable. This needs to be reconciled. Since it occured after maintenance, likely need timed. And or the e-gap adjusted. Plugs checked as already discussed. Do an inflight lean mag check prior to landing. Do you have the correct plugs. Consider the BY style plugs. Check the leads for integrity with a high tension lead tester
Ensure the carb is adjusted for a 25RPM increase at idle when shutting down or what ever your manual calls for. Use the leanest approved setting.
Make sure you do not have induction leaks. Pressure test with blower side of shop vac with sock over outlet thru carb inlet and use soapy water.
Lastly, in my opinion, you should never clear fouled plugs as suggested. To often, pilots forget to richen prior to departure leading to massive cylinder damage. Use better powerplant management practices and FIX the underlying problems.
 
Getting fine wire plugs might be beneficial, they are less susceptible to fouling compared to the ones with a massive electrode. I know some to have replaced only the bottom ones with fine wire plugs to save costs, but this does limit your ability to rotate them.
 
Yup. I have an O-360 which is the smaller version of yours. Mag drop not good, ran rough on one side, plugs routinely fouled. Tried the leaned run up, leaned very aggressively on the ground. Used tricresyl phosphate with every fill. A little better, but not right.

Replaced the lower plugs with iridium. Runs beautifully. Well worth it.
 
If anything I would think the fridge keeps them humid so they would have corrosion after a while. Don’t get the idea.
 
Eagle_ said:
If anything I would think the fridge keeps them humid so they would have corrosion after a while. Don’t get the idea.
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Cold air can't hold as much moisture as warmer air, so the fridge or freezer will have dryer air in it. The water condenses on the evaporator coils and drains out into an evaporation pan under the fridge during the defrost cycle every 24 hours or so.

But spark plugs in a fridge? No need for that. Bag them up.
 
I like to keep them in order so it does make it a little harder to find a larger zip lock bag, which I have done in the past.

I was desperate to slow down the rust in my humid hangar after bead blasting them clean without a bag. So I stuck them in the fridge, it slowed down the rust.
I thought it might entertain some so I posted about it. I am sure it is not the best way to keep them but better than leaving them on my work bench during the hot summer months, imo.
 
The FAA recently approved a 100 octane no-lead fuel for all aircraft piston engines. It may take a while to find its way into FBOs, but it should reduce spark plug fouling better than 100LL.
 
Dan Thomas said:
Cold air can't hold as much moisture as warmer air, so the fridge or freezer will have dryer air in it. The water condenses on the evaporator coils and drains out into an evaporation pan under the fridge during the defrost cycle every 24 hours or so....
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There is a difference between absolute humidity and relative humidity. Colder air (above freezing) will have a lower absolute humidity, but most likely a higher relative humidity. It's relative humidity that determines the dew point.

I think refrigerated spark plugs was a joke. If not, when they are removed, water will immediately condense on them. If you are going to keep them in the fridge, ziploc or vacuum bag at room temp and store in fridge. Upon removal, before opening the bag, allow them to come to room temp.
 
Gary Ward said:
I like to keep them in order so it does make it a little harder to find a larger zip lock bag, which I have done in the past.

I was desperate to slow down the rust in my humid hangar after bead blasting them clean without a bag. So I stuck them in the fridge, it slowed down the rust.
I thought it might entertain some so I posted about it. I am sure it is not the best way to keep them but better than leaving them on my work bench during the hot summer months, imo.
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Why don’t you dip them in oil or WD-40 or some other type of lubricant and wrap them in some plastic, it should keep corrosion at bay.
 
Actually a fridge is a great place to store things to keep them from rusting. But don't RUN the fridge, use it as a storage place with dessicant packs to lower the humidty.

Fridges are very well sealed, so the desiccant packs last longer.
 
Therookguy said:
I don't want to pay $700 for all my spark plugs to get replaced. I read online that I can just do a high power run up around ~2000 RPM then lean to 50 RPM LOP for a few minutes to clear it up. Is this likely to work or just make things worse?
Click to expand...

Pulling, cleaning and reinstalling plugs is considered preventative maintenance and can be performed by a Private Pilot. I would resistance test them too while they are out. Just make sure to replace or anneal the copper washers.

Having said that, if this is happening often (I don't know when "last time" was), then I would put some thought into how I am leaning, especially on the ground during taxi and run-up.
 
Pinecone said:
Actually a fridge is a great place to store things to keep them from rusting. But don't RUN the fridge, use it as a storage place with dessicant packs to lower the humidty.

Fridges are very well sealed, so the desiccant packs last longer.
Click to expand...

This is a good idea, would be a good use for a broken fridge.
In the winter time I unplug a fridge and use it as a hot box to keep my chemicals from freezing.

IMG_9546.JPG

I use a thermostat and a heat emitter made for reptiles. I have used it for 3 winters now, keeps it at about 50°f inside.
IMG_9536.JPG
 
Eagle_ said:
Why don’t you dip them in oil or WD-40 or some other type of lubricant and wrap them in some plastic, it should keep corrosion at bay.
Click to expand...
Because I don't like to put anything on a fresh plug except aviation anti seize. And I am too lazy/busy to wrap each plug in plastic.
 
Gary Ward said:
I was desperate to slow down the rust in my humid hangar after bead blasting them clean without a bag.
Click to expand...
FYI: tupperware works just fine along the GOM for items like that. You can usually find an "unlimited" number of shapes and sizes to fit your need. If you want to bump it up a notch fabricate aluminum plug holder to fit the plastic container and keep them labeled/organized. This method worked great for several customers who kept 2 plug sets in rotation on a regular basis.
 
Bell206 said:
FYI: tupperware works just fine along the GOM for items like that. You can usually find an "unlimited" number of shapes and sizes to fit your need. If you want to bump it up a notch fabricate aluminum plug holder to fit the plastic container and keep them labeled/organized. This method worked great for several customers who kept 2 plug sets in rotation on a regular basis.
Click to expand...

I don’t think he would have/make time for that either :goofy::D
 
MarkH said:
Pulling, cleaning and reinstalling plugs is considered preventative maintenance and can be performed by a Private Pilot. I would resistance test them too while they are out. Just make sure to replace or anneal the copper washers....
Click to expand...
A note on annealing copper. It is the opposite to iron.
Copper: heat washer to glowing red with torch and drop into water. This will soften work-hardened copper.
 
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