Transient EGT rise after engine start; difficult hot starts

[azure]

Two out of the last three times I've started the engine, I've noticed that after about 30 seconds, my #1 EGT goes up to about 150F above the others and stays there for about 2 minutes, then comes back down again. There is no engine roughness, just the EGT.

I've also had more of a problem with hot starts than usual lately (Lycoming IO-360). Usually I can stop for fuel and restart the engine without much difficulty, even in hot weather. Yesterday I stopped at PTK for charts, spent ~10 minutes inside, then could not get the engine started for the return trip. OAT on the ramp was about 27C. A local mechanic tried his own technique for clearing flooded cylinders with no success (it wasn't actually clear to me that the thing was flooded though), and cranked the starter for long enough that I elected to let everything cool for 30 minutes, after which it started easily. Back at home, I tried restarting it immediately after shutdown and had the same problem. This time I tried the POH hot start procedure. After two tries I gave up and put it away.

Any chance these two phenomena are related? Again, the engine seems to run normally and I'm noticing nothing ominous, but I don't like it when anything in my airplane suddenly behaves differently for no apparent reason.

 

[N175PT]

Just speculation of course but with the warmer summer temps its possible at shut down fuel is percolating in the fuel lines between the flow divider and the injectors. When you start it, it takes a few seconds for the vapors to clear.
On the Second hot start issue....don't we all!
On fuel injection the best way to think of it is to always assume we're in a flooded condition and go from there. When cold we prime, pull it back to ICO, crank and when it fires push the mixture up.
When hot, fuel will push out of the injectors for two possible reasons. One fuel boil off in the lines as above but also if the engine stops in the right position the fuel pump can be left in the "down" stroke keeping the pressure up on the system.
So again we operate from the assumed flooded condition and crank while in ICO with the throttle cracked slightly.
In both cases we go from too rich to fire to a burn able mixture, trying to be quick enough on the red knob to catch it before it leans out and quits.
The problem is the grey area in between where you have been parked for maybe 30-60 minutes or more, now is it cold or is it not?
The above works 90% of the time for me, but sometimes you blow it and will just have to wait a while.
Tim

 

[JHW]

it's easy to think fuel and often that's right, but my hunch is mags. It's worth a look

 

[Tony_Scarpelli]

I remember a case where a guy ended up having to insulate his fuel line in the engine compartment for a similar reason. I agree with Jeff to check the mags.

 

[azure]

Thanks guys. I've been suspicious of these mags because of borderline high RPM drops during runup for over 2 years now. But my A&P has checked them several times and keeps saying they're fine.

Just to understand: how would a problem with the mags affect hot starting, but not cold starting? And how would it cause a brief EGT rise on only one cylinder?

 

[flyingron]

A lot of cranking (and even some over prime/boost pump use) can dump some raw gas into the exhaust. It burns there and screws the EGT reading.

 

[azure]

Folks... I think I must have confused things by mentioning both of these issues in the same post.

The EGT rise happens on cold starts too... it's not a hot start issue. From cold, I don't overcrank or really prime that much. No more than before.

The only connection between the EGT behavior and the trouble with hot starts is that both problems seemed to start around the same time. That's why I wondered if they might have a common cause.

My A&P is finally back at work and available. I mentioned the EGT issue to him today. He suspects an induction leak.

 

[comanchepilot]

I had hot start issues in the Comanche last couple years. New battery did not solve issue, but it cranked faster and longer. Rebuilt mags? Nope.

What worked was new spark plugs. Bingo. Ymmv.

 

[Clark1961]

Thanks guys. I've been suspicious of these mags because of borderline high RPM drops during runup for over 2 years now. But my A&P has checked them several times and keeps saying they're fine.

Just to understand: how would a problem with the mags affect hot starting, but not cold starting? And how would it cause a brief EGT rise on only one cylinder?

Mags are pretty simple for the most part. Coil, condenser (capacitor), points, and a timing cam. Both the coil and condenser can fail when hot but work when cold. Depending on the engine it may or may not be so easy to tell if there is a failure in flight without an in flight mag check. On the Frankenkota it is immediately obvious when a mag goes out because the TIT goes bonkers. I imagine on a N/A aircraft the engine would just seem a little rougher than normal. At any rate, do a mag check while in cruise...

 

[azure]

Mags are pretty simple for the most part. Coil, condenser (capacitor), points, and a timing cam. Both the coil and condenser can fail when hot but work when cold. Depending on the engine it may or may not be so easy to tell if there is a failure in flight without an in flight mag check. On the Frankenkota it is immediately obvious when a mag goes out because the TIT goes bonkers. I imagine on a N/A aircraft the engine would just seem a little rougher than normal. At any rate, do a mag check while in cruise...

There is no sign that a mag is failing completely. The EGT on 1 (ONE) cylinder goes up for a minute or two after engine start, hot or cold. There is no engine roughness. Nothing like this happens during flight, or even during run up. I don't see how a mag problem could affect only one cylinder, but then what do I know?

FWIW my first two thoughts were 1) spark plug problem or 2) tiny induction leak that closes when the intake pipe warms up. My guy thinks it's likely the latter. Thanks for the ideas, I'll post more after he's had a chance to look at it (hopefully tonight).

 

[Clark1961]

There is no sign that a mag is failing completely. The EGT on 1 (ONE) cylinder goes up for a minute or two after engine start, hot or cold. There is no engine roughness. Nothing like this happens during flight, or even during run up. I don't see how a mag problem could affect only one cylinder, but then what do I know?

FWIW my first two thoughts were 1) spark plug problem or 2) tiny induction leak that closes when the intake pipe warms up. My guy thinks it's likely the latter. Thanks for the ideas, I'll post more after he's had a chance to look at it (hopefully tonight).

No disagreement at all Liz. One other thing is the harness. It might give non-repeatable failures but it can be tested.

Of course, suspecting an intake leak is another reasonable thing to do. It would bother me to think it's a problem on hot start but not cold start but that is neither here nor there. Engines are frequently finicky beasts...

 

[azure]

Of course, suspecting an intake leak is another reasonable thing to do. It would bother me to think it's a problem on hot start but not cold start but that is neither here nor there. Engines are frequently finicky beasts...

Me too. Fortunately that's not the case, the EGT rise occurs both on hot and cold starts. If the EGT rise is an induction leak would that even be related to the hot start problem? Methinks not, but again what do I know?

 

[azure]

Weather today was too crappy and convective to fly anyway, so I conducted a small test. Started the engine, waited for everything to settle down and the oil & CHT temps to come up, then taxied over to the fuel pumps. I was about 15 gallons down anyway and prices are rumored to be about to go up. After fueling, I taxied back. Here's what I found:

On the initial (i.e. cold) start, the #1 EGT started rising immediately, peaking around 1300F. The CHT came up a little quicker on that cylinder than the others, but never showed any alarming trend. In short, very much like it was running leaner than the others. For about 2.5 minutes, then it came back down to the mid 1100's along with the other three and stayed there. I wound up with an oil temp of about 130 and CHTs around 200.

After fueling, starting wasn't as easy as the first time, but about what I would normally expect, about 10 blades or so before catching. This time all EGTs stayed around the same temp. #1 and #2 were occasionally 50-60* above the others, but this is fairly normal for this airplane.

It seems likely to me that the EGT rise happens when something is cold, and then returns to normal when things warm up, probably due to thermal expansion. It's not a first start of the day thing though, as my experience at PTK proved that given 30-45 minutes to cool down, it will happen on a semi-cold start as well.

Someone else at the airport also suggested a problem with the JPI probe as a possibility. Given the CHT behavior, I tend to think it's real, and most likely a tiny induction leak.

 

[gismo]

Weather today was too crappy and convective to fly anyway, so I conducted a small test. Started the engine, waited for everything to settle down and the oil & CHT temps to come up, then taxied over to the fuel pumps. I was about 15 gallons down anyway and prices are rumored to be about to go up. After fueling, I taxied back. Here's what I found:

On the initial (i.e. cold) start, the #1 EGT started rising immediately, peaking around 1300F. The CHT came up a little quicker on that cylinder than the others, but never showed any alarming trend. In short, very much like it was running leaner than the others. For about 2.5 minutes, then it came back down to the mid 1100's along with the other three and stayed there. I wound up with an oil temp of about 130 and CHTs around 200.

After fueling, starting wasn't as easy as the first time, but about what I would normally expect, about 10 blades or so before catching. This time all EGTs stayed around the same temp. #1 and #2 were occasionally 50-60* above the others, but this is fairly normal for this airplane.

It seems likely to me that the EGT rise happens when something is cold, and then returns to normal when things warm up, probably due to thermal expansion. It's not a first start of the day thing though, as my experience at PTK proved that given 30-45 minutes to cool down, it will happen on a semi-cold start as well.

Someone else at the airport also suggested a problem with the JPI probe as a possibility. Given the CHT behavior, I tend to think it's real, and most likely a tiny induction leak.

Any chance the exhaust valve doesn't seat completely until the cylinder warms up a little? I would expect the CHT dT/dS to be the same or lower than the other cylinders if that were the case but there are lot of other factors that influence CHT so it might not be possible to draw any conclusions from that.

An induction leak that seals up as temps rise could also cause this as you suspect. You might try leaning aggressively right after starting. If you can get to a LOP condition the EGT should go the other way as the induction leak changes.

 

[azure]

Any chance the exhaust valve doesn't seat completely until the cylinder warms up a little? I would expect the CHT dT/dS to be the same or lower than the other cylinders if that were the case but there are lot of other factors that influence CHT so it might not be possible to draw any conclusions from that.

That I can't say for sure (obviously). If the exhaust valve leaks when cold, would that not result in low compression? Compressions all checked out in the mid/upper 70s at annual, a little over a month ago. Of course, I first noticed this at least a couple of weeks later..

An induction leak that seals up as temps rise could also cause this as you suspect. You might try leaning aggressively right after starting. If you can get to a LOP condition the EGT should go the other way as the induction leak changes.

Sounds like a good idea. There's enough fluctuation in EGTs (all cylinders) during the initial warmup that it might be hard to determine just how LOP I am (too far and EGT will fall again as the mixture richens), but it's worth a try.

 

[azure]

I finally got hold of my A&P today. Apparently he already looked at it some time ago, just didn't tell me ... he did not find any sign of an induction leak. (Didn't check for a crack in the flange, but that likely wouldn't self-seal by thermal expansion.) He doesn't think it's an instrumentation issue but says that he will swap the probes to rule that out. We discussed pulling the jug to examine the valve, but he doesn't think that's warranted at this point. He recommends flying it for now as long as the initial rise doesn't get worse, and as long as it comes back down as it's been doing.

 

[azure]

Update: seems to have fixed itself. Friday I flew to TVC. On engine start in the morning at home base I saw a very slight rise in the #1 EGT, by about 40-50F which is practically in the noise. Starting up for the return trip, the engine should have been pretty cold as it had been about 5 hours, but no discernible rise at all. Next morning back at home I taxied to the pumps for fuel: same thing, no rise at all.

I discussed the poorly seating exhaust valve theory with my A&P and he said that after discussion with an engine specialist, he thinks that's unlikely since it wouldn't seat and then re-unseat repeatedly.

I have no idea what this could have been given what's been ruled out (assuming it has), but I'm not going to worry about it unless it comes back.

 

[JHW]

Update: seems to have fixed itself. Friday I flew to TVC. On engine start in the morning at home base I saw a very slight rise in the #1 EGT, by about 40-50F which is practically in the noise. Starting up for the return trip, the engine should have been pretty cold as it had been about 5 hours, but no discernible rise at all. Next morning back at home I taxied to the pumps for fuel: same thing, no rise at all.

I discussed the poorly seating exhaust valve theory with my A&P and he said that after discussion with an engine specialist, he thinks that's unlikely since it wouldn't seat and then re-unseat repeatedly.

I have no idea what this could have been given what's been ruled out (assuming it has), but I'm not going to worry about it unless it comes back.

makes me even more sure it's mags. It'll come and go until it gets bad enough to throw some new condensors and capacitors at it.

 

[gismo]

makes me even more sure it's mags. It'll come and go until it gets bad enough to throw some new condensors and capacitors at it.

??? Condenser is another (older) name for a capacitor. And IME the ones used in today's magnetos very rarely go bad and virtually never become intermittent.

 

[JHW]

maybe I'm just bad luck. Had it happen twice in the last 10 years manifested by hot hard starting. Age of the parts doesn't seem to be a factor.

 

[bbchien]

Worn impulse coupler.....

 

[Marauder]

Azure -- it may be nothing more than a fouled plug. You have the same engine model as the Mooney I fly. I created a thread over at MooneySpace to start documenting interpreting engine monitor data. The first two contributions are my fouled plug problem and another Mooney owner's stuck exhaust valve, you should be able to look at your downloaded JPI data and compare notes.

Fouled plugs are common, and unfortunately, so are stuck valves in the IO-360s. Check out this link, it may help: http://mooneyspace.com/topic/9650-engine-monitor-data-troubleshooting-thread/

As for hot starts, welcome to our world. Mooney owners have seen this challenge and have posted a number of "magical hot start procedures". There is a thread going on there now with people contributing on their techniques. Again, one of them may help.

Also, in the 22 years I have owned my Mooney I find that different environmental conditions make starting harder or easier. The worst being hot and humid.

Here is the link to the hot start thread: http://mooneyspace.com/topic/9646-hot-starts-io-360-now-as-easy-as-cold-starts/#entry109196

 

[azure]

Thanks. Unfortunately I can't view the images without being logged in, and the registration page looks like they really want you to be a Mooney owner (unlike Beechtalk, unfortunately). Could you PM me your JPI images?

Fouled plug is actually the first thing I thought of, but my mechanic doesn't think that's it.

 

[bbchien]

I actually agree with marauder. 2000 hrs in Mooney F&J- same engine. A fouled plug causes the ignition front to spread more slowly which means burning fuel in the exhaust just outside the exhaust valve-->higher EGT.....until the flame unfouls it.

The hot start is likely the impulse couple. Check your logs. I'll bet Benenson never had it replaced. Benefits both cold AND hot starting and is not a lot of work to replace. Just more critical in a hot start.

 

[Marauder]

Sorry Azure, I forgot that us Monneyiacs are a secret society

Here is the fouled plug photo and my description:

My first contribution is a fouled #2 cylinder plug on the left mag. You will notice that the #2 EGT temp (yellow arrow) was elevated right from engine start -- something I missed because a) I wasn't looking at the EGT temps and

the engine was running smoothly.


You will see when I took the rpm up to 2000 to do the run-up, the red arrow points to the dip in EGT temp and of course, now I felt it. I aggressively pulled the mixture at the blue arrow and then did a left right left mag check as indicated by the white arrows.

 

[Marauder]

The second more serious situation is a stuck valve. You will hear owners refer to it as "morning sickness". Here is the description from the owner who did have a stuck valve and the JPI data he had on it:

"The red EGT line that's dipping down is the #1 cylinder. The yellow line is the manifold pressure. This seems to be exactly what the OP was talking about."

Please keep in mind the valve can be stuck open as well as closed.

 

[azure]

Thanks Marauder. I don't have a recording monitor but my malfunction would have looked a little different. My #1 EGT rose dramatically at first and then came back down, and I never felt any roughness (though I didn't try to run it up like that). I suppose it's possible that the deposit was thin enough that it burned through after a minute or two, as Bruce suggests, then reformed during taxi after landing. In any case I ran it pretty hard for a while coming back from TVC, so hopefully the fouling is gone. I'm pretty religious about brutal leaning on the ground, so it's hard to understand how it could have fouled -- but then again I'm usually 100-125 ROP in cruise, so maybe it happened during flight.

I've discussed stuck valve/morning sickness with my mechanic as well. It would seem that it would have to be an exhaust valve stuck open to cause a rise in EGT, and he says that I'd definitely feel that.

As to the hot start issue, I do have doubts about the mags. My mechanic says that any decent shop would have replaced them when installing the new engine, but that's not specifically mentioned in the logs. They only mention modifying the ignition switch for dual mag operation and changing the P leads. Would the impulse coupling be logged separately or is it part of the mags? I can't find any entry about that either. I wonder if there was an oversight in logging, or if the mag replacement was subsumed under "as directed in the service manual"...

I think I need to insist that my mechanic IRAN my mags fairly soon.