It’s gotta be ignition, right?!

[201Steve]

Hey yall,

my number2 cylinder is an EGT and CHT outlier. 
 

running LOP,  it’s the lowest EGT and lowest CHT.  Makes sense: farthest from peak, and thus the coolest running.

running ROP, it’s the highest EGT and lowest CHT.  Doesn’t make sense: closest to peak- it should be the hottest. 
 

 
 

these conditions were tested at 8,000 feet while running WOT so it should rule out intake leak. Savvy said clean the injector, I have twice. No change. 
 

thinking about it more, WOT removes air from the equation.  EGT behavior says it’s the leanest cylinder in both mixture regimes, but the CHT doesn’t trend accurately to support the theory that its fuel related.
 

it leaves one other variable: ignition. Does the data presented point to it not getting the same energy spark as the other cylinders?
 

seems like a weaker spark would certainly track with it being the coolest CHT no matter the mixture condition. I know that while ROP, a weak spark should rise EGT’s. Would a weak spark lower EGT’s while LOP???

 

 Am I tracking all of this correctly? Thoughts?

 

 

[Shadrach]

Seems ignition related to me (cyl#2).  What cylinder where you using as a reference for leaning and what was the peak EGT number?

[201Steve]

8 minutes ago, Shadrach said:

Seems ignition related to me (cyl#2).  What cylinder where you using as a reference for leaning and what was the peak EGT number?

I did not capture actual peak in this sitting so the reference numbers to peak are not accurate per se. 

[Shadrach]

Ok. So your numbers make perfect sense. Remember raw EGT number has nothing to do with which cylinder is leanest or richest. Speaking specifically to Cylinder #2. It looks like it’s only firing on one plug. When ROP on a single point of ignition, the combustion event is burning slower than the other three cylinders.  This means a significant portion of the combustion event is still burning during the exhaust stroke and continues burning in the exhaust riser. That means less fuel burned in cylinder, lower CHT and higher EGT.  It looks like you run further from peak when on the lean side.  Was it running smooth LOP?

[Ragsf15e]

Also, what about cooling airflow?  It’s in the front.  My 2 runs middle of the pack, but 1 is always low cht just because it’s in the airflow.  Do you have the oil cooler below it or in back of the baffling ?  What about baffling elsewhere?

[mhrivnak]

33 minutes ago, Shadrach said:

It looks like it’s only firing on one plug. When ROP on a single point of ignition, the combustion event is burning slower than the other three cylinders.  This means a significant portion of the combustion event is still burning during the exhaust stroke and continues burning in the exhaust riser. That means less fuel burned in cylinder, lower CHT and higher EGT.

I think both plugs are working. Your description of why EGT rises during single-plug ignition is true regardless of whether the mixture is ROP or LOP. Try a LOP mag check, and you'll see the EGTs rise.

Given that, the LOP data does not look like single-plug ignition.

[mhrivnak]

@201Steve have you done a flow test? You basically aim each injector into a cup, run the boost pump for a short time, and then check whether all four cups got the same amount of fuel. It looks to me like the data you're showing would be explained by #2 getting less fuel than the others.

And have you done Savvy's recommended gami lean test and in-flight mag check? That would capture a lot more data about how #2 is behaving compared to the others.

[201Steve]

6 hours ago, Ragsf15e said:

Also, what about cooling airflow?

Could be. Always the potential it’s two events happening simultaneously but I didn’t want to muck it up by making that rare assumption yet. 
 

 

7 hours ago, Shadrach said:

Was it running smooth LOP?

It’ll run smooth deep into each regime. I basically lean to achieve desired CHT. Goal being 100+ degrees ROP, and best acceptable power output vs CHT in LOP. 

 

6 hours ago, mhrivnak said:

@201Steve have you done a flow test?

Not yet. But it’s on my list of things to try at some point. 

 

6 hours ago, mhrivnak said:

And have you done Savvy's recommended gami lean test and in-flight mag check? That would capture a lot more data about how #2 is behaving compared to the others.

I do a LOP mag check every now and then. Never noted anything dramatic by feel.  I also did a Gami lean test, about a year and a half ago. I’ll see if I can find the flight. 

[201Steve]

Here’s the gami test flight from Feb 2023. 

https://apps.savvyaviation.com/flights/shared/flight/6617815/4f0ac0bb-2ef8-4f45-bcc5-8d01fa7c4686

also maybe hard to read but the savvy report also. 

 

[Shadrach]

11 minutes ago, 201Steve said:

Could be. Always the potential it’s two events happening simultaneously but I didn’t want to muck it up by making that rare assumption yet. 
 

 

It’ll run smooth deep into each regime. I basically lean to achieve desired CHT. Goal being 100+ degrees ROP, and best acceptable power output vs CHT in LOP. 

 

Not yet. But it’s on my list of things to try at some point. 

 

I do a LOP mag check every now and then. Never noted anything dramatic by feel.  I also did a Gami lean test, about a year and a half ago. I’ll see if I can find the flight. 

Safe to assume that you didn’t do an inflight mag check when you observed the numbers in your OP?

[201Steve]

Correct

[OR75]

checked the probes ? easy to switch them and get that out of the way