Spark plug fouling while flying LOP?

[Fearless Tower]

Did a round trip ORF-PHX last week in the Baron and started to experience what I believe was fouled plugs on the right engine. Basically every third leg, I would get an excessive mag drop on the right mag. Running it up to at least 2200 RPM and leaning it out for at least a minute cleared the problem....until it would reappear. Strange thing was that I was running LOP the whole time in cruise (confirmed by the EGTs and CHTs on all cylinders of the engine monitor).

Is spark plug fouling a common problem with
IO-470s? I am still relatively new to them, but I know that plug fouling is pretty common in the lower plugs of O-300s like my 170.

 

[jesse]

I doubt the lop in cruise was the cause. You sure you weren't excessively rich at some other phase of the flight (approach, landing, taxi, shutdown, startup, taxi, run up) are all points between those legs where you could be getting too rich.

I'm sure you already know it but keep them as lean as absolute possible while on the ground. It's also easy to accidentally take things too rich in the approach to landing phase.

 

[docmirror]

Here's a guess: LOP ops = lower CHT, this leads to lower plug temps, this leads to operation outside the plug heat range, leads to misfires, which exacerbate the problem of too cold plug, which leads to fouling.

Found this:

http://www.brisksparkplugs.com.au/images/technical/heat_range_sparkplug.jpg

 

[Henning]

If you go full rich and low power on approach and sty rich for ground ops, you'll load plugs. The only time I'm full rich is when I'm full power near sea level.

Next question though, are you oil fouling or fuel fouling?

 

[Norman]

Next question though, are you oil fouling or fuel fouling?

That was my thought too. What's the oil consumption on the right engine?

 

[Ted]

How old are the plugs?

 

[Bill Watson]

You might try two things to get some additional diagnostic information.

1) Watch your individual EGTs during your mag check. They should all rise when running on 1 mag. Any cylinder that doesn't may have a problem. See Savvy Mag Check I've been doing EGT-only based mag checks for a year now but have no useful experience with it yet.

2) Do an inflight mag check. Why? See link above

 

[Ted]

A little more detail on my question.

If the plugs are old, resistance can increase in them (especially if they're Champions, which have a higher resistance than Tempest). This can result in a weaker spark, which might leave some of the plugs a bit more susceptible to fouling. You wouldn't have it in cruise, it would be during some other full-rich time, such as approach or landing. I had issues with this in the 310, new plugs solved the problem. This was with the old engines.

 

[comanchepilot]

A little more detail on my question.

If the plugs are old, resistance can increase in them (especially if they're Champions, which have a higher resistance than Tempest). This can result in a weaker spark, which might leave some of the plugs a bit more susceptible to fouling. You wouldn't have it in cruise, it would be during some other full-rich time, such as approach or landing. I had issues with this in the 310, new plugs solved the problem. This was with the old engines.

I used to have a fouling problem in my 1800 hr IO-540 - last annual we resistance tested all 12 and 7 failed. We obviously replaced 7 and since last November I have not had a single instance of plug fouling . . .

 

[Ted]

I used to have a fouling problem in my 1800 hr IO-540 - last annual we resistance tested all 12 and 7 failed. We obviously replaced 7 and since last November I have not had a single instance of plug fouling . . .

Nothing wrong with doing it that way.

I tend to be the sort that shotguns it. I find that ends up being cheaper because it then goes longer without another problem.

 

[comanchepilot]

Nothing wrong with doing it that way.

I tend to be the sort that shotguns it. I find that ends up being cheaper because it then goes longer without another problem.

In the long run I have found that smart labor is cheaper than parts and labor . . .

 

[ChitDisturber]

Sounds like you fowled then on the ground to me.

Also what was the DA in PHX? I've found in high DA conditions if you don't lean aggressively for taxi you get a bum mag check

 

[Fearless Tower]

A little more detail on my question.

If the plugs are old, resistance can increase in them (especially if they're Champions, which have a higher resistance than Tempest). This can result in a weaker spark, which might leave some of the plugs a bit more susceptible to fouling. You wouldn't have it in cruise, it would be during some other full-rich time, such as approach or landing. I had issues with this in the 310, new plugs solved the problem. This was with the old engines.

No clue on age.....I'd have to sift through the logs, but I suspect it has been a while.

I could be running too rich either in the climb of approach. Definitely not during taxi- I am pretty aggressive about leaning on the ground.

I'll see what the logbooks say.

 

[Fearless Tower]

Sounds like you fowled then on the ground to me.

Also what was the DA in PHX? I've found in high DA conditions if you don't lean aggressively for taxi you get a bum mag check

Don't recall, but I didn't have the excessive drop on the run up in PHX, but I did get it the flight before leaving ABQ in the wee hrs of the morning.

Like I said in my previous post, I always run lean enough on the ground that anything over 1200rpm will make the engine die.

 

[Ted]

In the long run I have found that smart labor is cheaper than parts and labor . . .

Agreed.

No clue on age.....I'd have to sift through the logs, but I suspect it has been a while.

I could be running too rich either in the climb of approach. Definitely not during taxi- I am pretty aggressive about leaning on the ground.

I'll see what the logbooks say.

You'd notice a miss or other issue in-flight when LOP if it was being caused by the climb phase. It usually isn't because you're running higher power settings. So my guess is old spark plugs with rich on approach.

If they're fouling easily, they're probably old. Then you make the choice whether to replace the offending plug(s) or change all of them. My experience is that an old plug will die and then the rest will follow. But, 12 plugs aren't cheap (if only one engine is doing it, not necessarily a reason to do the other engine yet).

 

[Fearless Tower]

Agreed.



You'd notice a miss or other issue in-flight when LOP if it was being caused by the climb phase. It usually isn't because you're running higher power settings. So my guess is old spark plugs with rich on approach.

If they're fouling easily, they're probably old. Then you make the choice whether to replace the offending plug(s) or change all of them. My experience is that an old plug will die and then the rest will follow. But, 12 plugs aren't cheap (if only one engine is doing it, not necessarily a reason to do the other engine yet).

Age is starting to make sense. I flew the airplane all the way from California to Virginia back in May when I bought it and hadn't experienced this. Only thing that changed since then was cleaning the GAMIs.

 

[Ted]

Age is starting to make sense. I flew the airplane all the way from California to Virginia back in May when I bought it and hadn't experienced this. Only thing that changed since then was cleaning the GAMIs.

On the 310 they started to go out about 6 months to 1 year after we took ownership of the plane. Only thing that changed was about 100 hours more put on them.

 

[flyingron]

Here's a guess: LOP ops = lower CHT, this leads to lower plug temps, this leads to operation outside the plug heat range, leads to misfires, which exacerbate the problem of too cold plug, which leads to foulingl]

Eh? Lower CHT than what? CHT's go down on both sides of peak. Cylinder cooling is arguably better on the ROP side anyhow.

 

[Tom-D]

Eh? Lower CHT than what? CHT's go down on both sides of peak. Cylinder cooling is arguably better on the ROP side anyhow.

Gotta remember Deacon's Red box is on the rich side.

Cooling due to the lack of fuel happens much faster on the lean side of peak.

On the rich side you will only burn the fuel you have O2 to support.

On the lean side you will only burn the O2 that you have fuel to support.

 

[Ted]

Eh? Lower CHT than what? CHT's go down on both sides of peak. Cylinder cooling is arguably better on the ROP side anyhow.

I have found that for typical fuel flows people use in real world operations, LOP is cooler.

But neither is cool enough to lead to plug fouling.

 

[Chip Sylverne]

Might not hurt to do a close inspection of the harness as well. Look at the contact springs in the dist block for corrosion or signs of arcing, check the insulators for little black dots (signs of arcing) and have the leads tested.

 

[docmirror]

Eh? Lower CHT than what? CHT's go down on both sides of peak. Cylinder cooling is arguably better on the ROP side anyhow.

Than what the plug heat range was designed for. There's a simplified chart in my post above.

I based my 'guess' on the fact it's happening over longer periods of time, and not as the plane is started or idled around the ramp.

 

[Fearless Tower]

How old are the plugs?

Plugs are Champions and have about 250 hrs on them over the last 7 years (previous owner hardly flew it the last 3 years).

 

[Ted]

Plugs are Champions and have about 250 hrs on them over the last 7 years (previous owner hardly flew it the last 3 years).

Champions have a higher resistance than Tempests, so they'll be more prone to fouling. Of course, 250 hours is very low time, but there much be something to the years aspect.

One thing you could try doing for procedure. I'm not sure how you're operating in descent and approach, but you could try leaving the mixtures leaned out at cruise position until very close to landing (some even leave them until landed on the ground) and see if that does something.

 

[flyingron]

Than what the plug heat range was designed for. There's a simplified chart in my post above.

I based my 'guess' on the fact it's happening over longer periods of time, and not as the plane is started or idled around the ramp.

But the question I was asking is why LOP should have lower CHTs than ROP? Sure both are less than peak, but most people don't operate there.

 

[Fearless Tower]

But the question I was asking is why LOP should have lower CHTs than ROP? Sure both are less than peak, but most people don't operate there.

It is because the CHT temps fall off more sharply on the LOP side of the curve. Yes, you can get lower CHTs on the Rich side, but you have to operate much richer than most people who run ROP do in order to achieve that.

 

[Ted]

But the question I was asking is why LOP should have lower CHTs than ROP? Sure both are less than peak, but most people don't operate there.

Because with ROP the decrease in CHT happens much slower. So people will typically not want to burn that much fuel. With LOP, little changes make a big difference.

 

[poadeleted20]

But the question I was asking is why LOP should have lower CHTs than ROP?

Depends how much rich or lean of peak you are. CHT's start low at full rich, rise as you lean up to peak CHT around 75-100 rich of peak EGT, then fall off as you go leaner. So, there are two f/a mixtures which achieve any given CHT, one ROP and one LOP.

That said, almost all folks will be operating in cruise somewhere between 100 rich of peak EGT, which puts them near peak CHT, to somewhere on the lean side of peak EGT, which is well below peak CHT. Almost nobody operates in cruise so rich that they are rich of peak CHT. That means folks operating ROP are almost always operating at higher CHT's than anyone operating LOP.

 

[kgruber]

Spark plugs can still lead foul LOP. Flying LOP doesn't eliminate the lead in 100LL. Still can happen, just not as likely.

 

[Jeff K]

I see alot of mention of CHT here however generally at LOP your EGT's are higher then ROP.... rarely ever less. Wouldn't this be more of a factor for the sparkplug then CHT since the temperature of it's nose/electrodes is more impacted by EGT then CHT?

 

[poadeleted20]

I see alot of mention of CHT here however generally at LOP your EGT's are higher then ROP.... rarely ever less.

Depends on just how far LOP you are, or how far ROP you are comparing. If you look at the curve on page 6 of Lycoming SI1094D, you'll see how this plays out.

Wouldn't this be more of a factor for the sparkplug then CHT since the temperature of it's nose/electrodes is more impacted by EGT then CHT?

That is correct -- EGT is directly driven by combustion temperature, which is driven by f/a mixture, and it is the combustion temperature which provides the heat to activate the lead scavenging agents. That said, you're going to have worse lead fouling when rich of stoichiometric than when lean of stoichiometric since being richer than perfect f/a mix results in unburned fuel which can deposit more lead. Only thing is that stoichiometric is not the same as peak flame temperature, which occurs slightly rich of stoichiometric. See this paper for the technical details.

 

[docmirror]

I didn't mention lead, or oil, or some other unburnt HC product of combustion in my mention of low CHT, so I'm not going to go into that. Frankly, I don't care what byproduct is causing the fouling of the plug, just that it stop. If the plug isn't kept hot enough, it will not burn off the byproducts of combustion(whatever they are). Over time, this can be a problem.

Solutions include getting a different plug for that temp, or running hotter. Inspection of the plugs hasn't been mentioned yet so there's no way to empirically say what they show. Pictures, including close up of the insulator area would be useful.

 

[Jeff K]

Depends on just how far LOP you are, or how far ROP you are comparing. If you look at the curve on page 6 ..

I was talking about how most of us operate LOP vs. ROP... although your chart clearly shows what I am talking about as well.... 25-50d LOP vs. ~150d ROP which goes to my point.... why the discussion surrounding CHT here when it's EGT that has the far greater impact on the cone and electrode temperature?

No need to answer... I've solved my own riddle...

P.S. And I do agree with you about more "unburned junk" floating about in an ROP environment. I've been running LOP going on 6 years now... engine/plugs clean as a whistle with a light white/tan ash generally. That just wasn't question I was pondering here.