Fouled plug procedure?

Pi1otguy

Pi1otguy

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Fox McCloud
Is there a recommended procedure for clearing fouled spark plugs? Specifically how long should we run at high RPM?

Last flight the left mag ran really rough during the runup. So I did what previous CFIs taught me. Increase RPM to ~2000, lean, and waited ~30 seconds. Rechecked and it was still rough. Repeated this at a higher setting and felt some roughness before it settled. About 45 sec. Finally passed the mag check.

I learned this from my first CFI, but I don't recall seeing a checklist for fouled plugs in the POH or any list from the flight school.
 
You need to pull the plug and physically clean it. Don’t continue relying on a lean run-up procedure to fix the problem.
 
RyanB said:
You need to pull the plug and physically clean it. Don’t continue relying on a lean run-up procedure to fix the problem.
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It's a rental, so are plugs usually checked during the 100 hr?
 
Pi1otguy said:
Last flight the left mag ran really rough during the runup. So I did what previous CFIs taught me. Increase RPM to ~2000, lean, and waited ~30 seconds. Rechecked and it was still rough. Repeated this at a higher setting and felt some roughness before it settled. About 45 sec. Finally passed the mag check.
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I discussed with my mechanic. He inspected the airplane and diagnosed it with lead fouling. For my aircraft and my situation, if I received rough mag during runup, he instructed me to lean as much as possible right before engine cutoff during runup @ 2000 rpm for 60 seconds (I use a timer). Then full mixture and test mags again. If rough then repeat for a second time. Test mags. If still rough then shut down and do not fly. Again, this was my mechanic for my airplane for my situation.

Your situation is not likely to be the same as mine.
 
Mongoose Aviator said:
. For my aircraft and my situation,
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I don't doubt you. Just odd that I don't recall an POH stating it.
Mongoose Aviator said:
Your situation is not likely to be the same as mine.
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In my experience I only have 60% success in clearing. The other 40% is fouling as a prelude to you guys discussing me in an ntsb report. Long ago I learned the hard way that failed spark plug can somehow foul the other plug, killing a cylinder. Airplane are funny creatures.

Edit: I hope G100UL makes fouling a thing of the past.
 
That is the procedure... for lead deposits, which I'd say is the most common issue faced with a failed mag check. Run lean at >60% power ish. If it fixes it, great. If not, maybe something else is wrong. It's even better if you have EGT / CHT gauge as you can see exactly what's going on. If a cylinder goes fully cold, might be a bad plug or oil or something. No amount of running this procedure will help if something else is wrong.

I've had dozens? of mag check failures, however, only two resulted in AOG - one bad plug and one oiled over plug (which kept it from firing and we couldn't clear it)
 
Pi1otguy said:
I don't doubt you. Just odd that I don't recall an POH stating it.
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Perhaps I was not clear. This is NOT for my type or model of aircraft. This is NOT in my POH. This is my mechanic providing me specific instructions for my specific aircraft.

Your situation may very well be different from mine and it may be smart and safe for your mechanic to advise you on what is best for the aircraft you are dealing with.

EDIT. After reading post from @kaiser. I do have a graphical engine monitor to be able to see the EGT & CHT on all cylinders. I love the information it provides.
 
WE used to do the runup and lean thing in the flight school, but I wanted to know when the other instructors were having to do that so we could fix it right. Clean those plugs. I switched to the REM or UREM37BY plugs for every engine we had that was approved to use them, and that stopped the fouling issues. Those plugs have the extended electrodes that have the gap well above the plug well that holds those deposits. They make a huge difference, but too few people even know about them. They're no more expensive than the regular plugs.

upload_2023-3-3_15-23-28.png

Tempest/Unison and Champion have charts on their websites showing which engines can take them.
 
Pi1otguy said:
odd that I don't recall an POH stating it.
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A lot of planes I fly, it was never an issue because the only time anyone would consider burning 100LL in it is those extremely rare occasions 80 octane wasn't available.

And some planes I fly it is what POH? One of them the Entire maintenance Manual is a single 8 1/2x 11 sheet of paper typed front and back.

Brian
 
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