Cold Start Issues, Loss of EGT

FPK1

FPK1

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FPK1
My plane has the Lycoming IO-390 engine with G1000NXi PFD and MFD with engine details on the MFD engine page. It's pretty new, was put in service in January 2022, and currently has 247 hours...

Pretty much every cold start now (outside temp never below 50f) a few seconds after the EGT tempuratures start to display, the #2 EGT temperature drops off for a couple seconds (bar drops, temp # gauge goes blank), the engine runs rough, and then it comes back to normal. It's been like this for about 50 hours now.

Additionally, only twice, the #4 EGT dropped off briefly at start or when preparing for run-up. But mostly it's the #2 doing this.

Manual says RPMs at start/warm up should be between 1000-1200 and I usually have it in that range.

Never have the EGTs dropped off "during" a run-up.

Twice during a take off climb, the #2 EGT dropped off very briefly, the engine ran rough, then after a second or two, back to normal.

Once, 90 minutes into a flight from my home airport after a cold start, the #2 EGT dropped off and engine ran rough for almost 15 seconds, then back to normal. During that time an in air mag check was performed and it was still running rough on each mag and both. But it cleared to normal in about 15 seconds. A few minutes later while in a near idle descent the #4 EGT dropped off for about 2 seconds, then came back normal.

Mechanic did cold intake leak test (passed), cleaned fuel filter, fuel injectors and fuel spider. Swapped #2 spark plug with #3. Swapped fuel injector #2 with #4.

The #4 EGT dropped before and after the swap and #2 EGT continues to drop during every cold start (at my home airport) even after the swap. Before the swap #2 EGT always ran the hottest, now #4 EGT runs the hottest.

For the last year and a half, my fuel comes from my home airport fuel truck. All these cold start issues happened at that airport. Only use avgas 100LL.

Never had the issue with warm starts, like after a $100 hamburger day trip.

I never "noticed" this issue during a cold start following a flight where I stayed overnight at another airport, and where I have usually purchased at least 25 gallons of their fuel (tanks are 61 total usable).

I'm pretty good at leaning, in the air and on the ground.

Any thoughts and recommendations for me or my mechanic would be appreciated!
 
FPK1 said:
bar drops, temp # gauge goes blank
Click to expand...
Can you clarify this bit, please?
Does the indication disappear instantly when the roughness begins, almost like the probe is disconnected? Or is it a gradual drop, over a few seconds?
 
Kind sounds like a sticky valve issue or weak valve springs for the inflight situation.
 
AV8R_87 said:
Can you clarify this bit, please?
Does the indication disappear instantly when the roughness begins, almost like the probe is disconnected? Or is it a gradual drop, over a few seconds?
Click to expand...
EGT # gauge "1400" drops off shows "----" and EGT graph slowly drops. Then after couple seconds slowly climbs back up.
 
It sounds like morning sickness (sticky/tight valves).
 
FPK1 said:
EGT # gauge "1400" drops off shows "----" and EGT graph slowly drops. Then after couple seconds slowly climbs back up.
Click to expand...
I would agree with the others on sticking valves, but the EGT going from 1400 straight to ---, with no gradual drop (at least over a couple seconds) has me pondering. Did I understand that correctly?
 
AV8R_87 said:
I would agree with the others on sticking valves, but the EGT going from 1400 straight to ---, with no gradual drop (at least over a couple seconds) has me pondering. Did I understand that correctly?
Click to expand...
The numbers click down over the couple seconds 1200... 1134... 1076... 997... then recovers clocking back up to normal. Runs rough during that couple seconds and you can feel it coming. You can also see bar graph dropping during those couple seconds and then it recovers moving back up.
 
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FPK1 said:
The numbers click down over the couple seconds 1200... 1134... 1076... 997... then recovers clocking back up to normal. Runs rough during that couple seconds and you can feel it coming. You can also see bar graph dropping during those couple seconds and then it recovers moving back up.
Click to expand...
next time you transition from some elevated engine speed down to something near idle, say a Mag check situation, watch your EGT and see how much time it takes the data to transition between the two states.

Usually there is some data filtering happening to smooth out the readings, and without knowing what that time constant is, you can't really be sure the instrument is responding in the same time frame as the incident you are wanting to measure is occuring.

In addition to the valve issues others suggested, sounds like you found which injector is flowing the least fuel amongst the 4...
 
Ok, so normal indication for a cylinder that's not firing.

How's your oil consumption? Plugs look ok? If on the ground, try to shut it down before it recovers. Then pull the plugs on that cylinder and inspect for excess oil or other fouling.
 
AV8R_87 said:
Ok, so normal indication for a cylinder that's not firing.

How's your oil consumption? Plugs look ok? If on the ground, try to shut it down before it recovers. Then pull the plugs on that cylinder and inspect for excess oil or other fouling.
Click to expand...

Very little oil consumption, about 1 qt every 12 hours. Mechanic says plugs have been fine... Thanks for the inspection tip.
 
FPK1 said:
It's pretty new, was put in service in January 2022, and currently has 247 hours...
Click to expand...
What is your warranty interval for both the airframe and engine? Perhaps before digging too deep, may want to see if any of this will fall under your warranty coverage.
 
The #2 cylinder is not firing for a few seconds and the EGT is telling you the cylinder is not firing.
Why is it not? Spark, fuel, air and compression are all it needs. So which is it? Moved plugs, didn’t help. Switched mags, didn’t change. So spark seems ok. Cleaned injectors and that also didn’t help. Is your fuel pressure doing anything funny? If not, fuel is probably ok. That leaves air or compression. Valves sticking? Air leak in induction?
 
jsstevens said:
The #2 cylinder is not firing for a few seconds and the EGT is telling you the cylinder is not firing.
Why is it not? Spark, fuel, air and compression are all it needs. So which is it? Moved plugs, didn’t help. Switched mags, didn’t change. So spark seems ok. Cleaned injectors and that also didn’t help. Is your fuel pressure doing anything funny? If not, fuel is probably ok. That leaves air or compression. Valves sticking? Air leak in induction?
Click to expand...

Very helpful thank you... No fuel pressure funniness I can see. A cold intake leak test passed, is that the "induction?" If so, that leaves "sticking?" 95% of the time it's #2 but it has happened on #4 too 5% of the time. So, still sticking valves you think?
 
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FPK1 said:
Very helpful thank you... No fuel pressure funniness I can see. A cold intake leak test passed, is that the "induction?" If so, that leaves "sticking?" 95% of the time it's #2 but it has happened on #4 too 5% of the time. So, still sticking valves you think?
Click to expand...

How many hours on the engine?

Try adding MMO, fly a couple a couple of hours, then do an oil change. If sticking valves it can help by cleaning up the valve stems.
 
FPK1 said:
Very helpful thank you... No fuel pressure funniness I can see. A cold intake leak test passed, is that the "induction?" If so, that leaves "sticking?" 95% of the time it's #2 but it has happened on #4 too 5% of the time. So, still sticking valves you think?
Click to expand...
I’ve heard about such things but I’m no aircraft mechanic. I just posed the questions based on first principles. What does your mechanic think? This may be a real pain to find because it’s brief and intermittent.
 
FPK1 said:
So, still sticking valves you think?
Click to expand...
Long shot, and probably already checked by your mechanic, but have you looked at your valve clearances?
A&Ps should chime in, but I was told that if they're on the tight side (out of tolerances) they could stay open as different bits expand at different rates.
 
Your systems are classic morning sickness caused by sticking valves. If you visit the vans forum you will find this is a common problem with the 390. You will need to ream the valve guides. The fact you are starting to see this inflight means you are very close to bending or have already bent a value stem.
 
Thank you all very much! This morning sickness, sticking valves, appears to be a significant Lycoming 390 engine issue. I checked the vans forums and there's so much talk about this and it's exactly what I'm experiencing right down to the number 2 EGT.

Sticky valve on a Thunderbolt IO390

Hi all, I have been dealing with a EGT sag on #2 with a little engine vibration just after startup for a couple of months. Never had an issue beyond a minute or so while first starting the engine until it finally occurred on departure. Under 200 hours on the engine so it was difficult to be...
vansairforce.net vansairforce.net
 
MooneyDriver78 said:
Try adding MMO, fly a couple a couple of hours, then do an oil change. If sticking valves it can help by cleaning up the valve stems.
Click to expand...

Isn't it a reportable or ban hammer offense to mention MMO on POA? :fingerwag:

I use it myself in the fuel, but only because it smells so good ... :dunno:
 
Daleandee said:
Isn't it a reportable or ban hammer offense to mention MMO on POA? :fingerwag:

I use it myself in the fuel, but only because it smells so good ... :dunno:
Click to expand...

I would not use it fuel because I don’t know if it’s safe for sealant in my wet tanks. And I don’t leave it in my oil, usually I add it, fly a bit and then do the oil change immediately afterwards.
 
MooneyDriver78 said:
I would not use it fuel because I don’t know if it’s safe for sealant in my wet tanks. And I don’t leave it in my oil, usually I add it, fly a bit and then do the oil change immediately afterwards.
Click to expand...

I don't add much but it seems to help with removing what little carbon I get from running mogas ...
 
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Jeff767 said:
The fact you are starting to see this inflight means you are very close to bending or have already bent a value stem.
Click to expand...

Probably not, they usually stick in the open position, which results in no compression and the loss of EGTs.
 
My A&P recommended I add Alcor TCP to my fuel. I added it to my last three top offs and for the first time no morning sickness on my cold start yesterday...
 
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FPK1 said:
My A&P recommended I add Alcor TCP to my fuel. I added it to my last three top offs and for the first time no morning sickness on my cold start yesterday...
Click to expand...

Good deal! For us experimental folks we use Decalin which is basically the same soup with a different label ...
 
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Jeff767 said:
Your systems are classic morning sickness caused by sticking valves. If you visit the vans forum you will find this is a common problem with the 390. You will need to ream the valve guides. The fact you are starting to see this inflight means you are very close to bending or have already bent a value stem.
Click to expand...
More often it's the pushrod that bends. Sometimes you can see the pushrod tube bent by the rod itself.

1709334649548.png

A little more serious:

1709334718548.png
 
FPK1 said:
My plane has the Lycoming IO-390 engine with G1000NXi PFD and MFD with engine details on the MFD engine page. It's pretty new, was put in service in January 2022, and currently has 247 hours...

Pretty much every cold start now (outside temp never below 50f) a few seconds after the EGT tempuratures start to display, the #2 EGT temperature drops off for a couple seconds (bar drops, temp # gauge goes blank), the engine runs rough, and then it comes back to normal. It's been like this for about 50 hours now.

Additionally, only twice, the #4 EGT dropped off briefly at start or when preparing for run-up. But mostly it's the #2 doing this.

Manual says RPMs at start/warm up should be between 1000-1200 and I usually have it in that range.

Never have the EGTs dropped off "during" a run-up.

Twice during a take off climb, the #2 EGT dropped off very briefly, the engine ran rough, then after a second or two, back to normal.

Once, 90 minutes into a flight from my home airport after a cold start, the #2 EGT dropped off and engine ran rough for almost 15 seconds, then back to normal. During that time an in air mag check was performed and it was still running rough on each mag and both. But it cleared to normal in about 15 seconds. A few minutes later while in a near idle descent the #4 EGT dropped off for about 2 seconds, then came back normal.

Mechanic did cold intake leak test (passed), cleaned fuel filter, fuel injectors and fuel spider. Swapped #2 spark plug with #3. Swapped fuel injector #2 with #4.

The #4 EGT dropped before and after the swap and #2 EGT continues to drop during every cold start (at my home airport) even after the swap. Before the swap #2 EGT always ran the hottest, now #4 EGT runs the hottest.

For the last year and a half, my fuel comes from my home airport fuel truck. All these cold start issues happened at that airport. Only use avgas 100LL.

Never had the issue with warm starts, like after a $100 hamburger day trip.

I never "noticed" this issue during a cold start following a flight where I stayed overnight at another airport, and where I have usually purchased at least 25 gallons of their fuel (tanks are 61 total usable).

I'm pretty good at leaning, in the air and on the ground.

Any thoughts and recommendations for me or my mechanic would be appreciated!
Click to expand...
The cold start problem acts like an air bubble is getting in the fuel system when the engine is shut down. As the system cools there may be a point where air can enter when a vacuum is formed due to contraction. The leak might seal up under pressure or heat and the air has to go somewhere, so out a fuel nozzle might just be the path of least resistance. Somewhere along the fuel supply and delivery system air is entering the fuel system, perhaps only when cold or intermittently when running.

This is just an idea. It is worth what you paid for it.
 
FPK1 said:
My A&P recommended I add Alcor TCP to my fuel. I added it to my last three top offs and for the first time no morning sickness on my cold start yesterday...
Click to expand...

Nice to see a problem described and solution found all within one thread. And, it’s an FAA approved product.

Is this the only solution for the long-term or are there other methods or actions to prevent the issue?
 
TrueCourse said:
Nice to see a problem described and solution found all within one thread. And, it’s an FAA approved product.

Is this the only solution for the long-term or are there other methods or actions to prevent the issue?
Click to expand...
The only real solution is to ream the valve guides. Morning sickness does not happen on every start.
 
Jeff767 said:
The only real solution is to ream the valve guides. Morning sickness does not happen on every start.
Click to expand...
Which is recommended by Lycoming at 400 hours (SB) but as we discovered here, and I saw on the Vans forum, issues begin much sooner.

Additionally, there doesn't seem to be any consensus on how to avoid it e.g. running rich, running lean, etc. I also learned there is a 2017 Lycoming maintenance manual about the 390C engine (and of course I have a C engine) and I need to look at that a little closer to see if there's a way to avoid this in the future.

I can't help but think the G100UL fuel will benefit this engine and thus avoid these problems.
 
If the Alcor TFP is working, it must be lead fouled valves. It's specifically to remove lead deposits on valves, rings, etc.
 
jsstevens said:
If the Alcor TFP is working, it must be lead fouled valves. It's specifically to remove lead deposits on valves, rings, etc.
Click to expand...
I believe it's helping, but I've only added it four times so far and that did lead to a cold start with no issues for the first time in a while. So time will have to tell
 
SB650, it’s happened to my 580 a couple of times now. With the exact symptoms you complain of. This is the intake pipe flange cracking or breaking off. Many times it can be faint so unless there is engine vibration, it seals.
 
Valve #2 failed the wobble test and my mechanic found lots of smudge in the center travel guide of #2, so I asked him to ream all the valve guides.

As noted above, it's a common problem with the Lycoming IO-390 engine and an SB requires an inspection by 400 hours. So lucky me I needed it at 250.

Lots of TCP in my future and can't wait for GAMI G100UL!
 
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