Flying LOP > why are the egt jumping up and down, any ideas ?

[Curtisb]

Hello, flying our Main overhauled engine io360 in a 1980 m20j after 50 hrs lop again with gami.

the delta  in ff is nearly 0 in our edm between all 4 cyl, what we never had before is, that now running

on the lean side, the egt begin jumping up and down and it feels something like not going round at all,

it’s not a big thing but you feel something….it’s not happening when rop, either before overhaul the engine…

anyone some ideas? Look at the video, thx

[ArtVandelay]

Hello, flying our Main overhauled engine io360 in a 1980 m20j after 50 hrs lop again with gami.
the delta  in ff is nearly 0 in our edm between all 4 cyl, what we never had before is, that now running
on the lean side, the egt begin jumping up and down and it feels something like not going round at all,
it’s not a big thing but you feel something….it’s not happening when rop, either before overhaul the engine…
anyone some ideas? Look at the video, thx

It’s like 5° variation?! You’re looking for a problem that doesn’t exist.

[RoundTwo]

2 minutes ago, ArtVandelay said:

It’s like 5° variation?! You’re looking for a problem that doesn’t exist.

Agreed. If it was an analog gauge, it would be imperceptible. 

Edited October 10, 2021 by RoundTwo

[N201MKTurbo]

I would think it was some electrical problem, but that would do it ROP. All I can think of is intermittent misfiring. If you richen it up a bit does it stop? 

[carusoam]

The problem clearly exists…

But the video of the JPI doesn’t seem to show it…

Lets see if we can better understand the problem, and it’s cause…

Then diagnose what is going on…

 

Lets start with a discussion of when the problem occurs…

1) During LOP, Not ROP?

2) How much LOP, what altitude? 5°F, 50°F, or 90°F?

3) FF is pretty light at <8gph… deep leaning may be closer to 6gph…

 

Sounds like… you may be going too lean, thus causing a skip to occur…

Enrichen to see if the skip clears out…

 

A Gami spread test is good for diagnosing how well balanced the FF is going through all of the FIs… a good thing to document next…

 

Then download your JPI data, upload it to Savvy… click the share button, post the link here…

Pp thoughts only, not a mechanic…

Best regards,

-a-

[Ragsf15e]

If you’re actually going for efficiency instead of just very low ff, being just barely lop, like 0-20 degrees c is a pretty good spot (depending on your power/altitude).  You should be at 65% power if using peak, 65-75% id be more like 10-20 lop depending on CHTs.  More than that and the engine will be more likely to miss a little and you are falling off the bsfc curve.  Lop, 9gph will equate to 65% power, so you’re way below that.

[PT20J]

Agree with @Ragsf15e. If you look at the BSFC curve, you'll notice it falls fairly linearly until it levels off on the lean side. Theoretically, it would continue with a roughly constant slope until the engine just stopped. The reason it levels off is that the cycle to cycle variation in power of each cylinder increases as the mixture strength decreases and the engine stops being more efficient and runs rougher. There is really no operational advantage to running leaner than around 40 F LOP.

Skip

[Curtisb]

@carusoam it was at 5.000 ft and the video shows how much LOP it was, the video shows the leaning process, thx for your many answers at all so far, guys…

if I am too lean, I canˋt rich it up at all,  without having nr #3 on the rich side again, see the video..-

maybe I have to add 1-2 " MP before leaning on the LOP side ? Is it that, what you all mean ?

[carusoam]

Curtis,

Find the Gami spread leaning test…

find out what fuel injector isn’t working correctly…

Get it cleaned…

Repeat Gami test to prove that you got it cleaned…

When cleaning it, try to capture whatever was stuck in there…

This will help determine if you have a bigger problem upstream…

Semi-blocked fuel injectors occur pretty often around here…. Not everybody gets one every year… but a few people will show their engine data around here annually…. Hunting a similar challenge…

 

At 5k’ engines can go very deep in the LOP range… before shutting off completely.

My nicely balanced IO550 was capable of 90°F LOP before shutting off at that altitude… only 50°F at about 10k’…

If the Gami spread is zero… that is a good way to not have skipping on one cylinder…

If the Gami spread is larger than zero, about 5gph still good, but skipping starts to get in the way of a good leaning…

If you haven’t performed the Gami test…. You are going to want to just to eliminate a bunch of wonderment… 

Let us know if you need more info about Gami and savvy…

Doing the Gami spread test is free, and can be done by most MSers on the fly…

having difficulty seeing the latest video… internet challenged this evening…   
 

What I do see is cyl#1 going much leaner than the others and Cyl#3  lagging….  See Rich’s advice below for that…

If you share your data, downloaded through savvy… it will point out exactly what cylinder is not happy…

 

A really good run-up can also help diagnose other challenges like spark plug health, and ignition timing…

PP thoughts only…

Best regards,

-a-

[N201MKTurbo]

You might want to swap your #1 and #3 injector nozzles.

[carusoam]

Internet speed problem….  First world challenge…

 

So….

Problem description….

1) while leaning…

2) Cylinder #1 turns off before Cylinder #3 even goes LOP…

3) That is the definition of a Gami spread that is too wide…

4) Bummer…

5) But, most likely Pretty easy to fix…

6) Cleaning FIs using Hopp’s #9 is a common next step…

7) Doing the baby jar fuel system balance test is often a tool used for this exercise….

8) There are a few things that can be done to identify why the fuel isn’t being delivered in a balanced way…

9) Then there are methods of fixing that…

10) Kind of a measure, test, clean, test, observe, then swap hardware….   Start with the cheap and easy first…

11) Cleaning a fuel injector is pretty easy…

12) Cleaning them all and doing a flow test of the entire system takes a bit more effort…

13) Sometimes Fuel injectors get accidentally swapped as some people don’t know how important LOP is to the end user….

14) Check your log books to see if the numbered fuel injectors have moved locations…

15) often swapping the least with the most… supplies enough balance to narrow the Gami spread…

16) how closely can you work with your mechanic?

PP thoughts only, not a mechanic…

Best regards,

-a- 

[Curtisb]

Thank you, do you believe #1 is already off, before #3 even reaches LoP while watching the video ? the edm shows a spread of 0 Ltr ff, when I push the peak and spread button

and we did the gami test a few weeks ago and nearly  all cyl peaked at the same ff, maybe 0,5 Ltr in difference….

i can work very close with our mechanic… I think will follow your description and clean all injectors first and then go down the list…

maybe really one changed the inc…. I will check,

thanks a lot !

 

[ArtVandelay]

When I run LOP my EGTs:

[carusoam]

Curtis,

You have described something that has changed…

So the Gami FIs are really good at minimizing the differences in FF to each cylinder…

 

Can you share the data from one of the flights that had the issue?

1) Download the data…

2) Send it to savvy…

3) click the share button…

4) Copy link here…

This way, we can sift through the mountain of data to see what is not working properly…

Sometimes, there are spark plugs that are changing their internal resistance towards infinity…

If you have Champion spark plugs… one of them malign not be firing strong enough to light a lean mixture…

If you have Champion spark plugs, do you measure their resistance?

If you want a short cut… hire Savvy to review the data…  there is an example around here of a Bravo owner who just posted some of his data… and the explanation of the challenge he had direct from Savvy (Paul Kortopates)

Best regards,

-a-

[Curtisb]

@carusoam here comes one example, i was flying LOP, the engine was running rough lower 35 l FF it was flyable, but you could fell something not going round like it should normaly with a fuel Flow of 35 L, in normal i could fly the Plane LOP with FF 32 Ltr and it was running smooth

 

https://apps.savvyaviation.com/flights/5369132/cd3e3ae5-03fa-4016-b75c-fd0a48ae33bc

 

 

Edited October 31, 2021 by Curtisb

[Curtisb]

@carusoam what is some kind of strange, a few days ago i flew a check flight and did the gami test 3 times and the Peak was at 32L FF all the time.. i have no explanation for this, i changed nothing on the hardware between those flights..

this is the link to this flight 10 days earlier

https://apps.savvyaviation.com/flights/5369129/735c1478-d9e6-42fd-af2b-aec50471d519

 

 

 

Edited October 31, 2021 by Curtisb

[Ragsf15e]

FF is not going to be the same every time.  It depends on altitude, temperature, MP, RPM, etc.  Instead of saying, “it ran at 32l ff last time…” you really need to find each cylinder peak egt and then lean past that last one.  Reference number of degrees (F since it’s a US engine) past peak for the last cylinder to peak.  You should be able to run easily about 20-50 degrees F LOP.  You would reference that as “20 degrees LOP”.  Fuel flow could be different for 20 LOP if temp, altitude, MP or RPM is different.

[carusoam]

Curtiss,

The first thing I see… the FF is not running steady during the flight…

Is it changing on its own, or is this something the pilot is doing a few times during the flight?

note the FF bumps up to 38 and 39 or so…. ?

Best regards,

-a-

[Curtisb]

@carusoam No, in this case, it was the pilot on a 2 hours flight to enrich the engine to ROP to retry the leaning process like it is described

on savvy , best regards

Edited November 1, 2021 by Curtisb

[Curtisb]

5 hours ago, Ragsf15e said:

FF is not going to be the same every time.  It depends on altitude, temperature, MP, RPM, etc.  Instead of saying, “it ran at 32l ff last time…” you really need to find each cylinder peak egt and then lean past that last one.  Reference number of degrees (F since it’s a US engine) past peak for the last cylinder to peak.  You should be able to run easily about 20-50 degrees F LOP.  You would reference that as “20 degrees LOP”.  Fuel flow could be different for 20 LOP if temp, altitude, MP or RPM is different.

Yes, I always lean with the edm730 past peak for the last cylinder, but I just wonder, it never peaked at this high fuel flow and began to run rough….I know it varies from flight to flight, but never before that much…. It never ran rough at 35 ltr FF…. It was always flying smooth down to 32/31 ltr ff in 5000 ft with 65%
i think, I have to look on the spark plugs / ignition with more lean mixture I think maybe there is something to do

[carusoam]

One thing to consider regarding FF instability… is the age and hours of the fuel injector system…

If you know the hours… that would be helpful…

It might be time for that units OH or R&R or something of that nature…

We can invite @M20Doc to see if he has additional input…

Byron is also a great resource for fuel injector knowledge… @jetdriven

Best regards,

-a-