Fouled Plug

[mulro767]

So I went out to fly today and did a normal run up and mags checked good. When I was cleared for takeoff I started to add power and before I released my breaks, I noticed my JPI EDM-700 was flashing. It was flashing a max difference of 170 EGT on #4. I discontinued and asked to return to the run-up area.

I did another run-up and this time with mags on both, the #4 EGT was very high 1560 and all others around 1420, all CHTs normal around 310. Switched over to R mag and there was engine roughness. On the L mag all EGT's evened out.

So I ran the engine leaned out for about 15 minutes on the ground and tried several more times with no luck. How long does it take to clear out a fouled plug? Any other suggestion before I remove the cowl? This is my second flight after my annual and he said all my spark plugs looked good.

[Marauder]

I couldn't tell if you were leaning aggressively when you were running up attempting to clean the fouled plg. Usually when I get a fouled plug, I will lean out aggressively on the ground and run it around 2k rpm. I have a GEM and I typically will see the offending cylinder. Rarely, would I need to pull the plug. But if I did the GEM narrowed it down.

[Marauder]

Sorry I responded too quickly. I see you leaned it. Can you tell on the JPI if it is just one cylinder that is causing the issue? I would expect all of your EGTs to be elevated a bit when running on one mag since the combustion is being done on one plug. On my GEM, if I have a fouled plug, I see that cylinder's EGT actually go down due to the misfiring or non firing plug.

[mulro767]

Yea I leaned aggressively at 2000 for about 5 minutes the first time and didn't see any difference. The #4 cylinder had the high EGT when running on both. On the right mag it ran rough. On the left mag it was smooth and all EGT's leveled evenly. I did a longer run up with mixture lean and it didn't help.

I'll head back out on monday and try again. Think I should do a longer run-up? I know these things sometimes fix themselves but not sure if there's anything else I can do before I take off the cowling.

[mulro767]

Yea I see what you're saying. A fouled plug would have a lower EGT on that cylinder? That would make sense.

[stevesm20b]

I think I would just pull the cowl and check the plug. Even in my B model it would only take about 30 minutes to remove and replace the cowl, and change the plug.

[Marauder]

Sorry for the delay in responding. On both mags, I would expect on my GEM to see higher EGTs on the cylinder with the problem. The rationale being that the fouled plug is causing the combustion to occur later in the cycle resulting in the flame front being down further in the exhaust (closer to the probe). When you switch to the smooth mag, the engine is running on 1 plug and all EGTs should be uniform but higher. When you switch to the bad side, the cylinder with the problem plug would not be firing or firing intermittently causing the lower EGT.

It has been a while since I had plug issues (I lean a lot on the ground), but I'm sure some of my esteemed colleagues will correct me if I have this wrong.

[Marauder]

Another possibility is that you have a cracked plug or a short in that plug. As was mentioned, should be a pretty easy process to pull the plug and check.

[Steve65E-NC]

Sounds like a partially plugged injector to me. I went through a spate of this. Then I started carrying, on board, the right wrenches and gun cleaning fluid for soaking and like magic the problem stopped.

[N33GG]

IMHO: Clearing a fouled plug should only take 10 - 20 seconds. Advance throttle to 2000 - 2200 rpm and lean to peak egt and hold for about ten to twenty seconds, depending on severity of missing. Retard throttle and enrich mixture and check mags left and right. If not cleared, repeat with higher throttle 2200 - 2400 rpm for 20 - 30 seconds. Retard throttle and enrich mixture and check mags left and right. If problem persists, you may have more than a fouled plug. I have cleared lots of fouled plugs and never taken more than about 30 seconds at high throttle and lean mixture. I cannot imagine clearing a plug taking anywhere near five minutes.

Just my two cents, based on thousands of hours flying hundreds of airplanes, for what it is worth.

[fantom]

Clearing a fouled plug should take less than a minute.

Since your plane just came out of annual something else may be up. Stop fooling around and get that cowling off first thing. Your engine is attempting to tell you something. Listen to it.

[garytex]

Fantom is right on track. You have a bad plug, or something that is equally pressing. Find it and fix it before it bites you. Check resistance across the offender, it may be very high.

[gregwatts]

Clearing a fouled plug should take less than a minute.

Since your plane just came out of annual something else may be up. Stop fooling around and get that cowling off first thing. Your engine is attempting to tell you something. Listen to it.

Ditto!

[KSMooniac]

If it runs fine on one mag but not both (or the other) then it is NOT a fouled plug, or a plugged injector! You have an issue with the plug, mag or harness, and it should be checked before flight. Just because it came out of annual doesn't mean it is all good, and in fact something could have been induced by the maintenance action. Your engine monitor has allowed you to pinpoint it down to a specific cylinder, plug and mag, so you have already saved a lot of the troubleshooting time.

[RJBrown]

If it runs fine on one mag but not both (or the other) then it is NOT a fouled plug, or a plugged injector! You have an issue with the plug, mag or harness, and it should be checked before flight. Just because it came out of annual doesn't mean it is all good, and in fact something could have been induced by the maintenance action. Your engine monitor has allowed you to pinpoint it down to a specific cylinder, plug and mag, so you have already saved a lot of the troubleshooting time.

Once again we have a maitainence induced fault. Someone OOPS during annual. Don't let him charge you for his mistake. You missed a flight cause HE messed up. He probably dropped the plug on the ground and didn't regap it. Or something as simple. Accept his apology with grace but not a bill.