One fouled plug whilst flying

[Derek]

Whilst flying I noticed my engine beginning to run rough, and EGT No.4 rising significantly.

I tried a few things in the air (un successfully) to remedy the situation but nothing worked.

After landing I removed and inspected both plugs, the upper plug was definitely fouled, however the lower plug looked fine.

Q. Should I be looking any deeper into this issue ? or is it a simple matter of replacing the fouled plug ?

A4M
IO-360
2 x mags
180 hours on all 8 plugs.

 

[Carl Froehlich]

Or bad plug, or bad plug wire. Do some resistance checks.

Carl

 

[gasman]

Clean both plugs, test and switch them. Or just throw in a new plug and test the wire.

 

[Mconner7]

Look at BEY plugs…no more fouling.

 

[lr172]

Q. Should I be looking any deeper into this issue ? or is it a simple matter of replacing the fouled plug ?
.

YES. Those plugs have A LOT of carbon deposits. Either it is running VERY rich or, more likely, there is an issue with the oil ring/cyl wall. What is your oil consumption rate? I am guessing from the pics that it is quite high.

 

[Carl Froehlich]

YES. Those plugs have A LOT of carbon deposits. Either it is running VERY rich or, more likely, there is an issue with the oil ring/cyl wall. What is your oil consumption rate? I am guessing from the pics that it is quite high.

The OP reported the top plug fouled, the bottom plug not fouled. This points to a bad plug, bad harness or a bad mag.

Carl

 

[lr172]

The OP reported the top plug fouled, the bottom plug not fouled. This points to a bad plug, bad harness or a bad mag.

Carl

bottom plug, while not fouled, has an excessive amount of carbon build up, as dos the top.. I didn't say there was anything wrong with the plug, but instead that cyl is either seeing excessive oil or fuel and warrants some investigation. The pic on the top plug is obscurred, so can't tell if it is fouled from lead or a carbon deposit that broke off from the piston top. But the chunk of something appears to be grounding the center electrode, though it it possible that the oil itself caused the fouling.

plugs don't foul due to the plug or harness going bad, though each of those can cause a no spark event. The foul when things that should burn off, do not or a piece of debris, like lead or a chunk of carbon get stuck between electrodes and prevents the spark from occurring.

 

[Derek]

Thank you all for your responses

Based on your comments it looks like I'll be needing to conduct further investigations, once again thanks for your responses.

 

[togaflyer]

Derek, You might consider pulling all the spark plugs and compare them to this cylinder. Recheck the compression and bore scope that cylinder. Check the Ohms on those two plugs and see if they fall into spec.

 

[Derek]

Update

Firstly thanks to everyone who has offered suggestions to my issue, here's the result of my investigations.

1. I've performed a leakdown on all cylinders, they are all mid 70's.
2. I measured the resistance of the old plugs including the one that was fouled, this came back at ~900ohms
3. I measured the resistance of all the HT leads, this came back as ~42 ohms.
4. Based on what I'd discovered / learnt, I elected to replace all 8 plugs.

I then flew the plane with all new plugs for ~1hour. All went well until I was on final, when cylinder 4's EGT started to rise above all the others. My assumption at this point in time was that the problem still existed.

Back in the hangar I pulled both cylinder 4's plugs, remember these have only 1 hour run time. You can see that the problem I had with No. 4's upper plug is beginning to develop (RH plug in the picture). My guess now is that I have a faulty right magneto.

 

[lr172]

Firstly thanks to everyone who has offered suggestions to my issue, here's the result of my investigations.

1. I've performed a leakdown on all cylinders, they are all mid 70's.
2. I measured the resistance of the old plugs including the one that was fouled, this came back at ~900ohms
3. I measured the resistance of all the HT leads, this came back as ~42 ohms.
4. Based on what I'd discovered / learnt, I elected to replace all 8 plugs.

I then flew the plane with all new plugs for ~1hour. All went well until I was on final, when cylinder 4's EGT started to rise above all the others. My assumption at this point in time was that the problem still existed.

Back in the hangar I pulled both cylinder 4's plugs, remember these have only 1 hour run time. You can see that the problem I had with No. 4's upper plug is beginning to develop (RH plug in the picture). My guess now is that I have a faulty right magneto.

First, you must be running incredibly rich to get a plug to look like that left one after 1 hour of use, so suggest doing some reasearch on optimum mixture and set your idle mixture. Second, that right plug is soaked with wet oil and even after an hour is getting actual thick carbon build up. This point to a problem of some type in that cylinder. Just too much oil getting into the combustion chamber. It is possible all that black on the left plug came from oil, not excessive richness, just too hard to tell on a pic. Your first set of pics showed a pretty thick carbon build up and that is typically a sign of too much oil as opposed to running too rich.

It is possible that your no spark issue is ignition related and two most likely sources are the wire (need to wiggle and move it around while testing to find the problem if it is intermittent) or possibly an issue inside the Mags cap (carbon traces or eroded post). Also possible that the plug is getting carbon fouled and that is the reason it stops sparking.

It is hard to diagnose EGT issues not knowing probe health or location, but the EGT numbers you show are very low relative to most I have seen and that makes me think you may just be running too rich. Strongly suggest you go to 3000" and set up for 75% power after cleaning all of that black off the plugs. Then slowly dial back the mixture until the EGTs hit a peak temperature and then start falling. Then set your mixture to 100* richer than the peak you oberved. Fly around for and hour and see what your plugs look like. Also, the CHTs are very low. What was your engine doing when that pic was taken? Even at idle I would expect a fully warmed engine to have CHTs well above 225. I suppose if this was idle at 80 MPH it might make sense; I have never really observed CHTs on finial, but on the ground they should be higher. The EGTs in the pic make more sense if you were at idle.

I would suggest getting some help to figure out where all the oil is coming from in #4. First guess is a broken oil ring or possibly extensive glazing from break in.

EDIT: the more I think about this, the more I wonder if the primary source of your issue is a filthy rich idle mixture. Your plugs can run nice and clean at high power, but if your idle mixture is too rich, by the time you taxi back to pull the plug, it is now coated with carbon build up from the few minutes at idle. THough I still think you have at least a moderate oil issue. This would also partially explain why the engine ran fine for an hour and then stopped sparking as soon as you pulled to idle on final. Excessively rich mixtures can be hard to light via spark and showcase any weakness in the ignition system.

Larry

 

[avrojockey]

Larry is on the right path...those plugs are really fouled pointing to a mixture or ring problem.

I assume the wet one is the bottom plug

What do the other cylinder's plugs look like?

 

[Derek]

Here is more detail

The screenshot of the engine monitor was taken on final, rate of decent at that time was 300fpm, air speed was 84 knots, OAT was 55 degrees F, engine rpm 1400rpm. This may explain why my CHT's were low at that particular time.

The plug in on the right in the last picture is the upper plug.

Leakdown test was performed on a hot engine. If I had a broken piston ring, I would of expected it to show up at that time. If however a ring was broken, I would of thought that both plugs would be fouled, not just the upper.

I've set peak EGT at 1250.

 

[lr172]

The screenshot of the engine monitor was taken on final, rate of decent at that time was 300fpm, air speed was 84 knots, OAT was 55 degrees F, engine rpm 1400rpm. This may explain why my CHT's were low at that particular time.

The plug in on the right in the last picture is the upper plug.

Leakdown test was performed on a hot engine. If I had a broken piston ring, I would of expected it to show up at that time. If however a ring was broken, I would of thought that both plugs would be fouled, not just the upper.

I've set peak EGT at 1250.

Oil control ring is what controls how much oil gets left on the cyl wall. broken or not, it has no impact on compression readings. Ther are also two compression rings and those, if broken, will show low comp test results. Both plugs are fouled, just the one that didn't spark is wetter, as once it stopped sparking the temp dropped to the point of not burning off the oil. They are coated with a SIGNIFICANT (Caps for emphasis) amount of carbon, far beyond what should be expected from 100's of hours of service, let alone 1. Happy to back off you you don't agree. If it were me, my next step would be setting idle mixture.

I have no idea what you mean by "I set peat EGT at 1250." It peaks where it peaks.

 

[avrojockey]

If you find that it's an oil ring problem, this is one of recommended fixes...

https://resources.savvyaviation.com/wp-content/uploads/savvy_pdf/savvy-oil-control-ring-solvent-flush.pdf

Larry is right the EGT temp is not consequential...relative temps and peaks are what you're looking for.

 

[Derek]

OK that make sense

So its a oil control ring problem, combined with a rich idle mixture.

On shutdown idling at 1200rpm, moving the mixture to ICO the rpm rises ~40 RPM from memory, I always look for a RPM rise, not necessarily the precise amount.

As suggested I'll adjust the idling mixture as recommended by Airflow Performance, as well as looking into the oil control ring solvent flush.

Thanks once again for all your advice.

 

[lr172]

So its a oil control ring problem, combined with a rich idle mixture.

On shutdown idling at 1200rpm, moving the mixture to ICO the rpm rises ~40 RPM from memory, I always look for a RPM rise, not necessarily the precise amount.

As suggested I'll adjust the idling mixture as recommended by Airflow Performance, as well as looking into the oil control ring solvent flush.

Thanks once again for all your advice.

Just for clarity I didn't say it is an control ring problem or an idle mixture problem. Those were my speculations and first guesses, but just guesses. I only said that you have some issue that is causing your plugs to carbon foul. We have limited data here with no real eyes on the engines, nor an ability to test a variety of hypotheses. Diagnostic exercises are far more involved than what has been discussed here.

First, at 1200 you are no longer just on the idle circuit, so cannot do an idle mixture test there. Second, the RPM rise method can be difficult to execute with any level of precision and instead recommend the lowest MAP approach at 800 RPM. If you do it too quickly, a 200* rise can look like a 40* rise. The rise occurs with something like a 1/4 or 1/2 turn of the knob just before the engine dies. It is also different with a carb vs servo, so need to be carefull with internet advice. With the amount of what appears to be black soot on the plugs, it is hard for me to imagine that some phase of engine running is not too rich. Though it is possible that it is all coming from oil burn; I can't run my finger over it to determine which it is.