Surefly Mag Check - One EGT misbehaving?

[Ragsf15e]

Ok, first off, using the power of my EDM-930 engine monitor, I now know that this has been happening for over a year.  The engine runs smooth, starts easy, etc.  LOP or ROP, the engine seems fine.  There is a SF Mag on the left and a standard mag on the right.  Why does the #4 EGT rise so much more than the others during the mag check?  

Here's what I know... 

My mechanic says the plugs all get rotated at annual.  This was happening before my last annual.

This cylinder was actually overhauled at last annual and it was happening before/after that.

The SF is 2 years old and the harness (Kelly) was new with the SF.

This cylinder is my leanest running cylinder, but not grossly lean (I have GAMIs to about 0.4 spread)

 

(Green is rpm, purple is #4 egt)

[PT20J]

It can't be mag timing because that would affect all cylinders.

It can't be an induction leak or fuel issue since that would show up on the right mag as well.

That pretty much narrows it down to something related to the left ignition on cylinder 4. Since you have pretty well eliminated the spark plugs, that leaves the ignition harness or the SureFly. I would test the harness with an ignition harness tester and I would call Surefly tech support and see if they have any ideas. I think the Surefly has a separate coil for each lead.

Skip

[Browncbr1]

Make sure the top of your plug that touches the harness spring is not corroded.  use a pin wire brush cone to clean if needed.  Sometimes, it’s not the plug, but the spring that has a little corrosion on it.  But, in my past experiences, it resulted in egt drop off.  Atleast something to check. 

[Will.iam]

Borescope particularly the exhaust valve of number 4? Maybe not fully seating? Spitballing here. 

[Will.iam]

Oh nevermind glossed over the fact egt is normal in both and on left mag. 

[carusoam]

That’s a tricky situation….

Might be interesting enough that @kortopates may want to take a look at it… (Funky single EGT out of sync, during run up, with a sure fly mag)

As if a fuel injector is semi-blocked, but has a normal response on the regular Mag…

 

Great annotations Rags!

 

Single high EGTs can be caused by….

1) Blocked fuel injectors that alter the air fuel ratio to a lean mixture… (wouldn’t be Mag dependent)

1.1) leaky exhaust valve can allow burning fuel mixture to escape early…. (wouldn’t be Mag dependent)

2) Sparks that aren’t strong enough to initiate the fuel burn in a timely fashion… so fuel mixture is still burning after the exhaust valve…

3) Plug, wires, connections for that plug are probably going to show something… (a high resistance plug may stand out like this… or a plug that has been damaged or lost it’s center electrode may misbehave like this…)

 

4) It might be an easy test to swap in a different wire, plug, connectors…. (But you did this at annual….?)

 Might want to share this with the SureFly people…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[Will.iam]

Well the only thing you haven’t swapped out is the spark plug lead and the surefly. Since the former is pretty easy to money wise to test, I would swap out the lead and see if the problem follows or at least you can rule this park plug wire out. 

[carusoam]

Is that a Maggie set of ignition wires on the SureFly?

Best regards,

-a-

[Ragsf15e]

6 minutes ago, carusoam said:

Is that a Maggie set of ignition wires on the SureFly?

Best regards,

-a-

It’s a Kelly on the SF.  I have a Maggie on the right mag.  I hadn’t heard of them when I got the SF or I would have got a Maggie.

[Ragsf15e]

On 9/22/2021 at 1:28 PM, PT20J said:

It can't be mag timing because that would affect all cylinders.

It can't be an induction leak or fuel issue since that would show up on the right mag as well.

That pretty much narrows it down to something related to the left ignition on cylinder 4. Since you have pretty well eliminated the spark plugs, that leaves the ignition harness or the SureFly. I would test the harness with an ignition harness tester and I would call Surefly tech support and see if they have any ideas. I think the Surefly has a separate coil for each lead.

Skip

SF tech support responded pretty fast.  Here’s their answer:

Drew

 

The SIM utilizes a wasted spark system. One coil fires two cylinders on opposing banks. If it were a coil inside the SIM acting up it would happen on 2 opposing cylinders. My guess is if it’s an ignition issue you are probably looking at harness or plugs. Spark plugs should be gapped at .022. You will also want to check the plug resistance which should be 4K to 7K Ohms.

 

Blue Skies

 

Shane

[Will.iam]

Well i did have a finewire sparkplug go bad on me 24 hours into use. Only found that out by swaping the sparkplug with another sparkplug and the problem followed the plug. I couldn’t believe a new plug with less than 25 hours had failed but that is infant mortality for you. 

[DXB]

9 minutes ago, Ragsf15e said:

SF tech support responded pretty fast.  Here’s their answer:

Drew

 

The SIM utilizes a wasted spark system. One coil fires two cylinders on opposing banks. If it were a coil inside the SIM acting up it would happen on 2 opposing cylinders. My guess is if it’s an ignition issue you are probably looking at harness or plugs. Spark plugs should be gapped at .022. You will also want to check the plug resistance which should be 4K to 7K Ohms.

 

Blue Skies

 

Shane

Makes sense regarding two opposing cylinders; I thought normal plug resistance is generally 1K to 5K  Ohm per Tempest at least, not 4k-7k... mine are generally 1-2k Ohm when I check, rarely above 4k...is that a problem?

[Will.iam]

I don’t remember where i read it but any sparkplug above 5k ohms should be replaced. I was shocked when i tested my sparkplugs after i bought the airplane and the champion plugs in the engine none of them where under 5k one was 500k and 2 where over 1M ohms! I triple checked as I couldn’t believe the engine ran as well as it did but that’s the data i got.  Course maybe that’s why the mag overhaul center said my mag had heat stress and they had to replace two gears that were burnt and recommended i goto 250 inspection next time as 500 was too long. 

Edited September 23, 2021 by Will.iam
To and two are not the same siri!

[PT20J]

At the museum where we have a lot of big radials and therefore a lot of plugs, we use 5K ohms as the no go max. The older Champions had a removable resistor element that was problematic. These can be identified by looking down the barrel. If you see a slotted screw head, it’s the old type. Champion switched to an encapsulated resistor similar to the Tempest design several yeas back. I’d be surprised if there’s any difference between brands now. My Lycoming rebuilt came with Champions and at 250 hrs they all measure less than 2K. 

Skip

[carusoam]

The low numbers for resistance are good…

With Mooneys we are usually looking for anomalies like we see with Champion plugs that drift towards infinity…

Nice to have the JPI for a good part of the problem solving…

I don’t think we have a spec for resistance, as that wasn’t a requirement to check..

5k ohms sounds like a good line in the sand…

PP thoughts only…

Best regards,

-a-