Large EGT difference / stuttering at idle after flight

[bdash]

This evening after flying from KPAO home to 1O2 I taxied over to my hangar and was taking care of some post-flight tasks while letting the airplane sit idling at around 800rpm. I happened to glance at the engine monitor and noticed that the EGT reading for cylinder 4 was significantly lower than the other three cylinders (1080, 1080, 985 and 750 degrees respectively). I hadn't noticed any abnormal differences in the EGT during flight, and I don't recall ever having seen such a large difference while idling on the ground.

I ran the engine up to 2,200rpm to do a mag check. The EGTs were all within around 50 degrees between cylinders at that power setting, and the mag check showed the same consistent drop between left and right that I've always seen, and a consistent rise in EGTs across cylinders. This suggests to me that the ignition side of things is working fine.

After the mag check, I let it idle at around 1000rpm. I could hear a brief  stutter / change in the engine sound, every 5-10 seconds, that appeared to correspond to a 10-20º drop in EGT before they climbed up to their previous values. I've not looked closely at the EGT at idle before so I'm not sure if the fluctuation is normal, but I've definitely not heard the stutter before. 

Sadly the engine monitor, a JPI EDM 830, appears to be on a firmware version that is unable to download data to a USB drive. JPI has said that updating the firmware requires removing the unit and sending it in to them, so I've been putting it off. Unfortunately that means the only data I have is a couple of shaky videos of the engine monitor captured on my iPhone and my average memory.

I'll be giving LASAR a call in the morning to see if they can take a look at it. Until then I'd be curious to hear any theories as to what could be the culprit.

[Andy95W]

Was your mixture at full rich?  If yes, I'd call it borderline normal- unless something has changed recently or this behavior is new, based on similar conditions.

[bdash]

4 minutes ago, Andy95W said:

Was your mixture at full rich?  If yes, I'd call it borderline normal- unless something has changed recently or this behavior is new, based on similar conditions.

When I noticed the large EGT difference, I had leaned the mixture aggressively for taxiing. I then went full rich for the mag check. I'm not 100% sure if I leaned the mixture again after that, while watching it idle at 1000rpm.

[carusoam]

Can you download the data the old fashioned way?

With the engine warm there are a few things going on at the same time....

It is better to have and share data, then to guess...

Expect one cylinder is unhappy.  Could be one plug...

Could be a champion with high resistance...

Could be a valve misbehaving...

Just guesses...

Post what you have... then do a run-up... post that data as well... run-ups are good at identifying spark and mag issues...

check your logs for what plugs are in there... If champion, check their resistance...

Best regards,

-a-

[bdash]

3 minutes ago, carusoam said:

Can you download the data the old fashioned way?

I'm not sure what you mean by this. The EDM 830 sporadically displays "DATALOG ERR" during flight, and has never written anything to any USB drive I've inserted. I'm not convinced it's even logging the data it's generating. If you're aware of some way other than a USB drive to retrieve data from an EDM 830, I can definitely give it a go.

[carusoam]

Handling data is what these devices do for a living.  JPI devices have been doing this since the 90s.

Start with their website. To see what is available for your device.  The thumb drive might be a specific type.  Connecting by cable also requires some basic technology... your system my have two options...

It is worth trying to determine what it takes... do you have any odd sockets in the panel you don’t recognize? Looks like a 1/8” headphone socket...

The engine monitor has two uses...

• Monitoring CHTs and EGTs in flight....
• Problem solving... which may require sharing data with somebody....

You have just moved from basic monitoring to basic problem solving...

That is why we have expensive engine monitors, not just a couple of TCs and matching analog gauges.

PP thoughts only, not a mechanic...

Best regards,

-a-

[bdash]

The manual for the EDM 830 has instructions for downloading the data to a USB drive. I've confirmed that everything is correct with the USB drive (the EDM 830 can see a firmware update if I copy one onto the same drive, but for whatever reason the updater doesn't permit updating from the firmware version I presently have). The EDM 830 manual does not mention any other mechanism for retrieving data, nor do the system diagrams suggest there is any other means to do so. As I mentioned in my original post, the firmware version that the EDM 830 has installed is an older version that is reported to have issues with data logging, including the "DATALOG ERR" that I often see. I'm doubtful that it's even logging any data.

I understand the value of an engine monitor for troubleshooting. It's also invaluable for managing the engine while flying the aircraft. Given that I fly frequently and have little downtime between flights, I've not yet found a good time to remove the engine monitor and ship it to the manufacturer to be updated or repaired. I'd rather not be flying for weeks with nothing but an analog CHT and EGT gauge on a single cylinder to go by. I was expecting that I'd be able to wait until another maintenance event such as my annual inspection when the airplane will otherwise be unusable to deal with that.

Edited January 24, 2019 by bdash

[gsxrpilot]

First of all, EGT's at idle power and especially full rich, are meaningless. Even doing a run up on the ground full rich, is also meaningless other than to check for a fouled plug.

If you want to check the ignition system, go fly and do an in-flight lean mag check. Check the SavvyAnalysis website for their Test Profile for detailed instructions.

And at your earliest convenience, pull that JPI and send it in for the upgrade it needs to download data. Next, create an account on SavvyAnalysis where you can upload and analyze the data. The account is free. You can even share a link to data from a specific flight and let us all take a look at it. This service is also free :-)

Report back after doing the above. In the mean time, don't worry about it and go fly.

[ilovecornfields]

53 minutes ago, bdash said:

The manual for the EDM 830 has instructions for downloading the data to a USB drive. I've confirmed that everything is correct with the USB drive (the EDM 830 can see a firmware update if I copy one onto the same drive, but for whatever reason the updater doesn't permit updating from the firmware version I presently have). The EDM 830 manual does not mention any other mechanism for retrieving data, nor do the system diagrams suggest there is any other means to do so. As I mentioned in my original post, the firmware version that the EDM 830 has installed is an older version that is reported to have issues with data logging, including the "DATALOG ERR" that I often see. I'm doubtful that it's even logging any data.

I understand the value of an engine monitor for troubleshooting. It's also invaluable for managing the engine while flying the aircraft. Given that I fly frequently and have little downtime between flights, I've not yet found a good time to remove the engine monitor and ship it to the manufacturer to be updated or repaired. I'd rather not be flying for weeks with nothing but an analog CHT and EGT gauge on a single cylinder to go by. I was expecting that I'd be able to wait until another maintenance event such as my annual inspection when the airplane will otherwise be unusable to deal with that.

If your software version is too old you have to perform two software upgrades- one to a slightly newer version and then another to the newest version. You can’t go directly from really old->new. If you call them they will talk you through it and send you a how-to document. Just write down ALL your settings first and have a backup plan if the update bricks your unit.

[bdash]

Just now, ilovecornfields said:

If your software version is too old you have to perform two software upgrades- one to a slightly newer version and then another to the newest version. You can’t go directly from really old->new. If you call them they will talk you through it and send you a how-to document. Just write down ALL your settings first and have a backup plan if the update bricks your unit.

Yep, I'm aware of the need to do the two step update from old versions of the firmware (pre-v3.44 upgrade, then the normal upgrade). For whatever reason the update to the intermediate version never completes. JPI support said that they don't have any suggestions besides sending it in.

[carusoam]

Sounds like you need some real customer service...

borrow a newer unit while your unit is sent back to get the updates you want to have.

should take about a week if it were planned well.

This type of customer service would have to come from your local Avionics shop, or directly from JPI.

Do you have a local avionics shop that did the install originally?

JPI isn’t known to have real customer service. They exist. But you need to know what you are asking for...

What does it take to get the two step update done?

Is it time for an instrument upgrade?

Is it time for an instrument supplier upgrade?

Back to guessing at the original challenge...

• sounds like an over rich situation may be occurring... see if adjusting the mixture knob helps any...
• could be a fuel set-up challenge... are you familiar with the rpm rise when pulling the mixture out to ICO?
• might be the champion spark plug challenge showing up.

When doing a run-up on the ground, do it slow enough to see the EGT rise on all four plugs, for each mag... do they all rise and fall evenly?

+1 for doing a mag check in flight...

+1 for using Savvy to get a better understanding of options...

A work horse has different needs then a casual weekend aviator. What’s the next steps if this stays the same or gets worse?

Is down time a minor inconvenience or a major expensive problem?

PP thinking out loud, not an instrument guy...

Best regards,

-a-

[Bob - S50]

If there is a big EGT difference, and since you've already checked your magneto, to me that suggests a mixture issue.

If you had a plugged injector or other fuel delivery issue, I would think you would still have a big difference at cruise power settings.  You said you don't.

If you only have a big difference at idle, to me that suggests an intake air leak.  At full power there is very little difference in air pressure between the inside of the intake and the outside of the intake so very little air gets sucked in and the mixture is about the same as the other cylinders.  However, at idle the pressure inside the intake is a lot lower than outside, maybe 20" of MP?  That would be conducive to sucking a lot of air into any cylinder that had an intake air leak.  That would cause that cylinder to be much leaner than the others.  If you have all the other cylinders running brutally lean, then the cylinder with an air leak will be even leaner.  It may be so lean that it occasionally does not burn well.

If that is the case, if you enrichen the mixture while at idle, does the stumbling go away?

Then the question becomes, how much do you want to spend to fix it?  If it only affects the engine at idle I'm not sure I'd be willing to spend a lot of money.

I'll be curious to see what LASAR says.

[kortopates]

You could be using too large of a USB memory stick to work with your JPI; especially with the older firmware. I can't recall the limit but either use an older smaller one or check on their website. Or it could mean your units memory has a problem and it needs to go back to repair.

@Bob - S50 above is spot on regarding a possible induction leak at idle, given it's going away mag check RPM that's suggestive of your sniffle valve (cylinder drains) not sealing. You could pinch off the cylinder drain hose to see if that helps but the folks at Lasar will check this for you. But any leaks absolutely need to be fixed, but finding them is more expensive than fixing them but given your monitor is pointing to #4 it shouldn't be that hard.

Edited January 24, 2019 by kortopates

[mike_elliott]

1 hour ago, Bob - S50 said:

If you only have a big difference at idle, to me that suggests an intake air leak. 

Coupled with the IO360's are prone to have the intake tubes loosen, (gasget crush might be involved) I would check here first. Good call Bob.

[jaylw314]

9 minutes ago, kortopates said:

 

@Bob - S50 above is spot on regarding a possible induction leak at idle, given it's going away mag check RPM that's suggestive of your sniffle valve (cylinder drains) not sealing. You could pinch off the cylinder drain hose to see if that helps but the folks at Lasar will check this for you. But any leaks absolutely need to be fixed, but finding them is more expensive than fixing them but given your monitor is pointing to #4 it shouldn't be that hard.

Wouldn't a stuck sniffle valve affect all the cylinders though?

[kortopates]

Indeed, that's most common to combine a bank of cylinders or all. Mine is one per side.

 

 

Sent from my iPhone using Tapatalk

 

[bdash]

I spoke with LASAR and the immediate reaction after I described the symptoms was also that it sounded like an intake leak. Since my aircraft is conveniently based at Lampson Field, they're taking a look at it now.

[bradp]

I also had issues updating firmware with a 730.  I tried umpteen usb sticks until I asked JPI and they sent me one in the mail that was compatible.  Since then I found one from the early 2000s that seems to work and keep them separate for just the JPI. 

[Marauder]

I also had issues updating firmware with a 730.  I tried umpteen usb sticks until I asked JPI and they sent me one in the mail that was compatible.  Since then I found one from the early 2000s that seems to work and keep them separate for just the JPI. 

Early versions of the 730 and 830s were limited to USB sticks that were less than 4 Gb in size. I think the older units had a 2 Gb limitation.


Sent from my iPhone using Tapatalk Pro

[Flymac]

Just went through same issue/finally biting the bullet with my 730...for years the data downloading has never worked (would only record a 2 min file or such)...no parameter change in the world fixed it, tried many USB sticks, even the "JPI" one they sent...no change.  A factory reset didnt fix, and trying the firmware update would not recognize the new data files on the USB I downloaded from the JPI website(JPI techs on phone couldnt figure it out either).  Had to go back to JPI to update firmware.  I had 2.13, which I read between the lines as that version didnt seem to really support the downloading as it should, or as mentioned above, must have been very picky on its USB sticks!

[copierdynamics]

Data, data, data. Do a quick visual in the cylinder after a compression check, then lap the exhaust valve or pull the cylinder and replace the valve. Fly.

 

[bdash]

To close the loop on this: LASAR took a look and found that the spark plugs in cylinder 4 were oily. They didn't observe any other abnormalities in the cylinder. They cleaned, gapped, and reinstalled them. We'll be keeping an eye on this going forwards.

While they were looking into this, they noticed that the engine monitor was not correctly grounded. JPI believes this may explain some of the erratic readings I'd seen. Since we had a few weeks of very wet weather here in Northern California, LASAR took that opportunity to pull the engine monitor and send it to JPI to be updated to the latest software. It was then reinstalled, with the incorrectly-wired ground addressed. Everything has looked good since then, and I've been able to download and analyze the engine data from my recent flights. In the event that I notice any more engine abnormalities we'll now have data to look at.

[Yetti]

From flight school we were taught to idle when sitting between 1100 and 1200 rpm.   I carried that policy forward and it seems to work well.  no fouled plugs and compression were 79 across the board last annual

[Hank]

1 hour ago, Yetti said:

From flight school we were taught to idle when sitting between 1100 and 1200 rpm.   I carried that policy forward and it seems to work well.  no fouled plugs and compression were 79 across the board last annual

I generally idle at 1000. The key is to lean the engine waaaaay back.

[Yetti]

The other thing I was taught on transition is to use the cruise settings in the pattern.   only pull the throttle back.  Then the mixture comes back on rollout.   Everything gets shoved full forward for a go around.