Help Diagnosing Rough idle / cool/erratic egt

[Ragsf15e]

My F model just came out of annual.  I have a new cylinder (#2), Surefly mag and a newly IRAN right mag.  The only cylinder that’s not been recently overhauled is #4.  It was running fine coming into annual, but my IA noted some oil in the bottom and some deposits on the exhaust valve and stem.  Compression was fine.  So I flew the plane 3 times to break in #2 and I’ve noticed slightly rough idle.  I was thinking “morning sickness” but then I noticed #4 egt.  It’s really low at low power. It’s also erratic.  It seems to clean up for the mag check and during flight, but comes back at low power.

Today we borescoped #4, looks ok, same deposits but valves open and close fine. Compression check was just fine.  Plugs look good.  IA took rocker box cover off and springs were ok, valve didn’t seem to “wiggle”.

What am I looking at? Failed egt probe? Maybe exhaust or induction leak to #4?  I looked at jpi data from a couple months ago and it was fine.

 

This one was only on the ground, but is a good example.  RPM between 1000 and 1600.

 

This is startup. Mag check and takeoff.  Egt is erratic at low power.

[Hank]

I'd recheck the plugs in #4. Clean them, check the gap, put them in the tester. And check resistance through the plug body, should be well under 5000 ohms. But I'm not an A&P, although I did fight a similar issue in my C. New plugs, new ignjtion harness and a change from copper-based antiseize to graphite-based. But maybe it was going from a toothbrush-sized antiseize brush to a nail polish-sized brush that helped, as I also cleaned each sparkplug hole thoroughly with contact cleaner before installing the new plugs.

[Guitarmaster]

Have you done an in-flight mag check yet?

[Ragsf15e]

2 hours ago, Guitarmaster said:

Have you done an in-flight mag check yet?

I did do that on the last flight.  I did it LOP per the Savvy guidance and it was fine.  The ignition doesn’t seem to be the problem.  I’m open to any possibilities, but if it was a spark issue, I think the egt would be hotter.  Right now I’m starting to think probe issue, or intake / exhaust leak?  Maybe the roughness was my imagination staring at faulty egt data? 

 

*btw, if you do an in flight mag check with a Surefly, even a new one with the new “quicker start up”, maybe you should reduce power before going from Surefly off, through mag off, back to both.  Loud pop that will get your attention.  At 1700rpm during the normal ground mag check, it’s just a quiet skip.  At 2500rpm it’s more exciting.

[Yetti]

Fuel delivery to #4

[EricJ]

EGT probes/wires, or the baffling.   If the baffling was apart there may be a leak that wasn't there before if something isn't back where it should be.

[carusoam]

The best way to share JPI data is done by sending the link from savvy...

This allows people with varying backgrounds to look at the data that they are most interested in...

If we ‘Cherry pick’ the data... we will all be looking at the same thing... possibly missing what an MS expert would want to see...

Sharing the data, may take clicking on a share button...
 

I do like the data labels... EGT4 went from off line-ish to back in-line... in a step fashion...

EGT4 stands out through the entire run up procedure on both mags...

How does the GAMI spread look? #4 looks consistently cold like it may be getting more fuel than the others... or it has more dead-ish (high resistance) spark plugs than the others...

Did somebody accidently move FIs around?

What plugs do you have?

Probably a good idea to note the Surefly in your avatar data fields... EGTs can be affected by timing and spark strength...

Pp thoughts only...

Best regards,

-a-

[Ragsf15e]

38 minutes ago, carusoam said:

The best way to share JPI data is done by sending the link from savvy...

This allows people with varying backgrounds to look at the data that they are most interested in...

If we ‘Cherry pick’ the data... we will all be looking at the same thing... possibly missing what an MS expert would want to see...

Sharing the data, may take clicking on a share button...
 

I do like the data labels... EGT4 went from off line-ish to back in-line... in a step fashion...

EGT4 stands out through the entire run up procedure on both mags...

How does the GAMI spread look? #4 looks consistently cold like it may be getting more fuel than the others... or it has more dead-ish (high resistance) spark plugs than the others...

Did somebody accidently move FIs around?

What plugs do you have?

Probably a good idea to note the Surefly in your avatar data fields... EGTs can be affected by timing and spark strength...

Pp thoughts only...

Best regards,

-a-

I’ll see if I can upload and share it from saavy. 

The Gami spread has been consistently 0.4 for the last couple flights, so not bad, and the engine runs smoothly LOP.

I have Gami injectors and Tempest fine wires.  The injectors are in the correct locations and the spark plugs tested ok at the annual last month.  They looked ok when we pulled them yesterday.

It just seems like the lower power (taxi and ground time) is where it’s erratic.

[EricJ]

4 minutes ago, Ragsf15e said:

I’ll see if I can upload and share it from saavy. 

The Gami spread has been consistently 0.4 for the last couple flights, so not bad, and the engine runs smoothly LOP.

I have Gami injectors and Tempest fine wires.  The injectors are in the correct locations and the spark plugs tested ok at the annual last month.  They looked ok when we pulled them yesterday.

It just seems like the lower power (taxi and ground time) is where it’s erratic.

Rough idle could be an intake leak, which is possible due to the cylinder work.   Check that the rubber intake couplers are all on snug.

[carusoam]

+1 for leaks being more noticeable during idle... and a much smaller percentage of air during high power operations...

But the going cold part makes it more interesting....

That sounds like three leaks on the other intakes(?) 

Best regards,

-a-

[chriscalandro]

It’s probably the fuel caps. 
 

but seriously, I’m thinking intake leak. 

Edited February 22, 2020 by chriscalandro

[Ragsf15e]

1 hour ago, EricJ said:

Rough idle could be an intake leak, which is possible due to the cylinder work.   Check that the rubber intake couplers are all on snug.

That’s what I keep leaning towards.  I’m gonna take a look at it this weekend and then check more thoroughly for leaks with my mechanic on Monday.  Probably swap the probe too just to be sure.

[Guitarmaster]

Ditto on the intake leak

I have an O470 that the front two cylinders would not participate when it was cold. Rough idle, but smooth run-up. You could watch the cylinders come to life in the run-up. Once warm, it would idle fine.
Found the leak under the number 5 riser and also at the boot where the balance tube connects.
Fixed that and idles great now!

When I had the Mooney, I had a devil of a time getting the intake tubes to seal against the cylinders. It took coating the gaskets with #3 Permatex Aviation sealer before I was able to finally get rid of the leaks.

[Ragsf15e]

Solved.

I really thought the induction leak was the best hypothesis, especially since the problem wasn't really visible at full power, only idle (for the most part - I did eventually find a few anomalies at full power).

Did you know that 3 guys (2 x A & Ps and 1 x Pilot/owner) standing next to the engine staring at the #4 cylinder can't see the exhaust studs & nuts?  It takes bending down lower to look up at them which I did this weekend when I went to look for an induction leak.  Below is what I found.

 

I looked at the ground run after annual and the first flight after annual.  The EGT is just fine until midway through the first flight when there are a few weird excursions.  Then it's always a bit wonky at low power for the next two flights and a ground run before I realized there was a problem.  The last flight I got a Carbon Monoxide alarm from my Sensorcon while taxiing in (40ppm).  Way higher than usual on the ground.  I still was showing 0 in flight.  I didn't start to put that together with the engine data anomalies until this weekend.

Based on the data from the ground run and first flight, I believe the nuts, washers and star lock washers were there at one point, but weren't torqued or fell off for some other reason.  All have been checked again.

This was a little scary after the fact.

Rags

 

[Guitarmaster]

Excellent! Glad you found the smoking gun!

[MikeOH]

Rags,

While I hadn't noticed any symptoms, I had this happen to ONE stud on my #2 cylinder.  I spotted it after pulling the cowling for a routine check (I try and do this every 25 hours).

Please check that the studs are properly torqued in the head; in my case the threads in the aluminum head were stripped!  That's WHY the nuts backed off; the studs would NOT support the tension for the required torque.

I had to heli-coil the head to fix the issue.

Edited February 25, 2020 by MikeOH

[Ragsf15e]

1 hour ago, Guitarmaster said:

Excellent! Glad you found the smoking gun!

I see what you did there! 

[Ragsf15e]

1 hour ago, MikeOH said:

Rags,

While I hadn't noticed any symptoms, I had this happen to ONE stud on my #2 cylinder.  I spotted it after pulling the cowling for a routine check (I try and do this every 25 hours).

Please check that the studs are properly torqued in the head; in my case the threads in the aluminum head were stripped!  That's WHY the nuts backed off; the studs would NOT support the tension for the required torque.

I had to heli-coil the head to fix the issue.

Good to know, thanks for that helpful insight!

[carusoam]

No exhaust stains to go with that smoking gun?

I was thinking if it was enough to have noticeable results in the instrumentation...

Exhaust stains and CO alarms would be present...

 

Great follow-up with pics!

Thanks for sharing the details, Rags!

 

Cooler EGT = exhaust leak !  (Put that in the memory bank for later) 

Best regards,

-a-

[Ragsf15e]

17 minutes ago, carusoam said:

No exhaust stains to go with that smoking gun?

I was thinking if it was enough to have noticeable results in the instrumentation...

Exhaust stains and CO alarms would be present...

 

Great follow-up with pics!

Thanks for sharing the details, Rags!

 

Cooler EGT = exhaust leak !  (Put that in the memory bank for later) 

Best regards,

-a-

On my last flight I did get that CO alarm from the sensorcon but it was only 40ppm which is higher than normal on the ground but not a huge increase (I usually have <20 on the ground and 0 in the air).

When I put her away this afternoon I wiped down the cowl and there is a very light exhaust stain along the aft edge of the lower cowl on the affected side.  Tough to see unless you’re specifically looking for it.

I guess this has been one more example of an engine monitor proving its worth.  It was directly responsible for showing me a problem existed and partially identified the exact problem.