Engine runup problem

[N601RX]

I had a problem durring mag check today. I suspect a fowled plug as the engine was  ran on the ground not fully leaned for a while.  I ran it up to 2000 leaned and it seemed to clear itself after a couple of minutes. I few minutes later it was missing again on one cylinder. 

How do others clear a fowled plug and how long does it take?

 

[carusoam]

When you cleared it, did you stay lean while on the ground?  or did you push the mixture back in?

O-360 or IO-360?  (O more likely to fowl than IO)

Left mag or right mag? (Engine monitor to help Identify actual cylinder?)

Lower plugs are more likely to fowl with lead deposits.  Large lead deposits are hard to get rid of without pulling the plug.  Pulling the plugs is not so hard.  Look for lead or oily plug.  (be ready with crush washers, torque wrench, and never seize)

How old are the ignition wires?

Following the procedure you outlined above, typically cleared my O-360 in a couple of minutes.  When I had a roughness that would not go away, I had the ignition wires replaced with good results.

Key thing here is to KNOW that it is a fowled plug and not something else.

Spark plugs are on the list of things you can do yourself (if you are familiar).  Consult your A&P if you are not.

-a-

[Hank]

When I have a rough mag check (O-360), I run up to 2000 RPM, lean it out for 50-100 RPM increase, and hold it there for 60 seconds. Then mixture rich, throttle back to 1700, and it has always run smoothly. The more often I remember to lean aggressively when taxiing, especially at larger airports, the less I have to do this. "Agressively" means about 50% travel of the red knob. Just remember to push it forward before takeoff!

If this won't fix it, talk to your A&P.

[KSMooniac]

There is no reason to run full rich on any Mooney on the ground until you're on the runway.

[jackn]

After start-up lean to rpm drop, enrichen. Just remember, mixture full forwrd for runup. If still fouling, i would suspect lead buildup on the plug.

[Skywarrior]

Same thing happened to me on a recent trip. While still in the run-up pit, I leaned a bit to dry off the plug(s), then re-did the mag check, which was then within limits.

OK, *now* I believe in leaning while taxiing.

 

Chuck M.

[DaV8or]

I lean aggressively after start and for taxi. Also I run about 1000 rpm for taxi unless a tailwind is pushing me to fast during taxi. I learned this sort of thing while learning to fly in the C152. The O-235 is notorious for fouling.

[Lood]

Ditto for me regarding aggressive leaning after start up and during taxi. However, I also lean very aggressively after landing. As soon as I'm down to taxiing speed, I pull the mixture right back - so much so that I have to push it in to be able to take power for the turn around on my home runway. The engine won't go higher than about 1440-1500 rpm without giving it some more fuel. If I do it any other way, I'm stuck with a rough running engine at my run up. Doing it this aggresively also mostly rules out a take off with a too lean mixture.

[DaV8or]

Quote: Lood

Ditto for me regarding aggressive leaning after start up and during taxi. However, I also lean very aggressively after landing.

[Immelman]

I have had several fouled plugs that would not clear unless going to full power (note: mixture rich) for a few seconds. If that doesn't fix it, its time to shut down and pull the cowl. I carry all the tools to remove/replace/clean plugs and also a brand new one as spare.

[N601RX]

The problem turned out to be a severely fouled plug.  Runs fine now.

[HopePilot]

I don't feel I've been taught how to clear a fouled plug correctly.  Everyone is saying they lean slowly.  Does anyone pull the fuel mixure about half-way for a second, then back to rich?  This seems to clear a fouled plug, but it seems harmful?

[Gone]

Quote: HopePilot

I don't feel I've been taught how to clear a fouled plug correctly.  Everyone is saying they lean slowly.  Does anyone pull the fuel mixure about half-way for a second, then back to rich?  This seems to clear a fouled plug, but it seems harmful?

[Gone]

double post

[richardheitzman]

I had an interesting conversation with a engine shop owner who talked about leaning on taxi. One thing he said is sticking in my mind. Leaning on taxi reduces fuel, increases temps and because of the lack of cooling air during slow taxi can allow the valves to overheat and boil the oil in the valve guides, reducing lubrication properties, and destroying the valve guides. This person was very against taxi lean. He said that if you suspect a fouled plug, run the engine UP to 2000+ rpms, leave it there for a while, and then back down to 1700 for the mag check. If the plug(s) are fouled then you need to stop and pull to get them cleaned up. ALSO make sure your idle fuel flow is correct as the problem could be "too rich" on the ground because the idle fuel flow is not set correctly. It was a very interesting conversation that I would like to here other comments for or against.

[Kwixdraw]

Leaning during ground ops should never be a problem as the % of power is so low. I would like to see the JPI readings on the ground but I would be hesitant to base a go-no go on them since I have no experience with it. I can tell you that mag drop and run up are not all there is to it. My J was on leaseback for some time and was always having issues with instructors that couldn't start the injected engine without flooding it or fouling the plugs. I went out to fly and had to go through a flooded start drill even though the plane had been sitting overnight. Taxied to runup and had bad mag drop on the right side. I brought the rpm up and leaned pretty heavily, thinking it was a fouled plug. Still had a bad mag drop but not as bad. Brought the rpm back up and leaned then added a bit bit of pressure to the cylinders by bringing the prop back 100 rpms or so and watching the egt. Run up was normal after that and I departed to a local airport with a 7700 ft elevation. Enroute I started to lean the mixture and the engine darn near quit. It picked back up when the mixture was on full rich but would not accept any leaning. 180ed back to the field and into the hanger. The plugs were normal but we found a bad capacitor in the right side of the dual magneto.  Don't assume it's a fouled plug because there can be other causes.

[bgpilot1]

I was having fouled plug problems on the bottom ones until I replaced them with fine wire spark plugs.  Haven't had any fouled plugs since.  I will check them all this month during annual but they have certainly helped.  I lean on the ground, and leave the mixture lean when landing as well.  My suspicion is that it is set too rich to start. 

[KSMooniac]

Richard, that is one of the silliest things I've ever heard!  I have a JPI engine monitor and watch the temps all the time.  The only time I'm full rich is when applying power for takeoff and on initial climbout.  After 1000' or so I start leaning in the climb to maintain 1250-1300 EGT.  I never go full rich unless there is a go-around or missed approach either.  So, I'm leaned on the ground all the time, and the CHTs and oil temps are always *much* cooler than they are in operation with takeoff power or even cruise power.  (I've never had a fouled plug either)

I think that is just another mechanic's myth that he is propogating without any data whatsoever.

[outermarker]

I just began to have a problem with my 66 E with respect to mags/engine. The plugs are clean and gaped correctly. The engine runs very smooth during the mag check. However, the engine runs rough and will not go to max rpm. Fuel pressure is good with and without the pump on. I am confused at this point. One day it flew great and then the plane sat in the hanger for about 4 months. The next time I wanted to fly.......well, that is why I am writting..all advice is welcome.......

[DaV8or]

Quote: outermarker

I just began to have a problem with my 66 E with respect to mags/engine. The plugs are clean and gaped correctly. The engine runs very smooth during the mag check. However, the engine runs rough and will not go to max rpm. Fuel pressure is good with and without the pump on. I am confused at this point. One day it flew great and then the plane sat in the hanger for about 4 months. The next time I wanted to fly.......well, that is why I am writting..all advice is welcome.......

[outermarker]

I would think that the fuel pressure would increase if a fuel injector had some degree of blockage. It seems that everything is fine until the engine gets about 2000 rpm.

[Gone]

I had a similar problem a couple of months ago.  I turns out my mixture was set too rich. 

[carusoam]

"I would think that the fuel pressure would increase if a fuel injector had some degree of blockage. It seems that everything is fine until the engine gets about 2000 rpm." - Outermarker

Interesting thought, but with three other avenues for the fuel to exit the system, the increase in resistance to flow would be rather small compared to the fuel flow controller higher upstream.

from an engineering point of view....

If one fuel injector was clogged, the other three would handle the increase in flow without much change in pressure overall.  The viscosity of fuel is pretty low and the actual flow is pretty minimal.  The fuel pressure is measured at the begining of the fuel injection system.

However, if fuel was flowing unevenly, it would show up visibly on the engine ananlyzer.  The offending cylinder would peak earlier than the others.

This is just my thinking out loud..........

Best regards,

[jackn]

Thought i had a fouling/leaning issue. #4 was always the 'fouled' plug. My mechanic didn't think it was a plug issue since it was an almost new fine wire properly gapped. Had him switch plugs around anyway. Problem followed the plug. Turns out plug was giving a very weak spark.

[outermarker]

just returned from running the engine again. Mag check was ok at 1600-2000 rpm. I leaned the engine and no noticeable increase in temp (only one probe) throughout the tests. The fuel rate was in the green with and without the pump running. Prop seemed to go from fine to course pitch without a problem. Just a normal, standard run up. What did turn up was manifold pressure would go to 30" at full throttle but the rpm would only go to 2200!!! I could still cycle the prop but 2200 was all I was reading with manifold at 30". Of course I was expecting 2700 rpm. I don't understand why this would cause the engine to run a bit rough at higher power settings. Again, the first part of this year the plane flew for about 40 hours without a problem. Then it sat these past 3 months and now this? Is the prop fooling me here?