High EGT on one cylinder (it's not the probe)

[carusoam]

Possibly...

Similar logic as a dead spark plug?

-Excess unburned fuel mixture departs the cylinder still burning=higher EGT...

-Lower energy released within the cylinder=lower CHT...

-but, the mixture would be different...

Same logic applied to the partial closed intake valve...

- all air is consumed, excess fuel (100LL) departs the cylinder, won't ignite until O2 is presented from other exhaust streams(?).

- risk1: compression is inadequate to allow a timely flame propagation. (?)

- risk 2: back fire in the intake system becomes a serious concern. (?). As a good fuel mixture will move back into the intake.

As far as exhaust lobes go...

-same logic, valve doesn't open all the way, exhaust doesn't easily depart the cylinder.

-exhaust stroke is pushing against higher pressure than 'normal'

-intake stroke is blended with more exhaust than 'normal'

-similar logic to high back pressure exhaust systems...

That's failure to open...

Failure to close usually leads to a valve crashing into the piston dome. This would be more typical of exhaust valves with burnt oil in the valve guides...

That's the best I have...

Best regards,

-a-

[Shadrach]

They never responded about checking the flow divider either.  Which is the next place I'd check in the fuel system.

[Super Dave]

I was thinking that if the intake valve was not opening fully, the mixture would get very rich thus slowing the flame front to the point that the combustion event is still happening during the exhaust stroke thereby causing the high EGT. I know this can happen when an engine is run very LOP. You can witness a second peak as combustion gets so slow that it continues in the exhaust. Not sure if it happens on the rich side. Someone ought to email Mike Busch.

Haven't had a chance to start looking at the valve train yet, but if we ever get this figured out, I think it's going to be something oddball like this.

Emailed Mike Busch over a week ago, but haven't heard back.

  

They never responded about checking the flow divider either.  Which is the next place I'd check in the fuel system.

Haven't looked at the flow divider either, but as I've said before, I just don't see how this could be poor fuel distribution. Take a look at 24:48 here:

https://www.savvyanalysis.com/flight/909304/3faa364e-3150-4c9d-a3a1-6177ecf13711

This is the flight where we ran several inflight diagnostics. At 24:48 I was looking for peak from the lean side on #2 and you can see that all cylinders peak simultaneously at 9.9GPH. Then, mixture was leaned to 8.1GPH for a couple minutes, and you can see that #2 went from 1655° at peak to around 1585° at 8.1GPH... that's 70°LOP.

[Cruiser]

I went back and looked at the first flight that you found the problem. #552 2-23-2015 where #2 EGT stayed high when the FF was increased at 2:15:48. All EGTs respond the same, in the same relative movement.

FF was increase to 11.7 and held there until 2:19:48 when it was first decreased to 11.4 but then rapidly increased to 12.2 after which the FF was held constant but the #2 EGT stayed high while the other three came down about 50°F and all remained there.

 

Since that time on all other flight I am really not sure I see a problem. The beginning of the above flight showed a 35°F difference between #3 and #2 and that is now about 70° but the EGTs are all responding in sync with each other.

Make a normal flight with normal operation and look at the JPI data

[Shadrach]

Haven't had a chance to start looking at the valve train yet, but if we ever get this figured out, I think it's going to be something oddball like this.

Emailed Mike Busch over a week ago, but haven't heard back.

Haven't looked at the flow divider either, but as I've said before, I just don't see how this could be poor fuel distribution. Take a look at 24:48 here: https://www.savvyanalysis.com/flight/909304/3faa364e-3150-4c9d-a3a1-6177ecf13711

This is the flight where we ran several inflight diagnostics. At 24:48 I was looking for peak from the lean side on #2 and you can see that all cylinders peak simultaneously at 9.9GPH. Then, mixture was leaned to 8.1GPH for a couple minutes, and you can see that #2 went from 1655° at peak to around 1585° at 8.1GPH... that's 70°LOP.

I see what you're saying. #2 appears to be behaving as it should, except for the number is inflated by ~150df.

[Piloto]

Dave

The plot offset on#2 is consistent with a voltage bias induced by the alternator/generator charging when RPM is increased at 00:10 on take off and decreased at 00:42 when RPM is decreased on landing. Notice that the offset is the same (119F) when running ROP during the climb (high RPM)or when leaning at 00:23. I don't think there is something wrong with the cylinder but check on the cylinder attaching and exhaust nuts. If they become loose or rusty the ground conductivity path to the case is reduced thus affecting the EGT and CHT readings.

If you have an incandescent landing light the #2 EGT reading is likely to increase when turned on together with the pitot heat.

One way of reducing the induced generator spikes (engine vibration) and offset you see on the plot is by connecting the generator/alternator case directly to the airframe instead of relying on the engine case.

José

[Super Dave]

DaveThe plot offset on#2 is consistent with a voltage bias induced by the alternator/generator charging when RPM is increased at 00:10 on take off and decreased at 00:42 when RPM is decreased on landing. Notice that the offset is the same (119F) when running ROP during the climb (high RPM)or when leaning at 00:23. I don't think there is something wrong with the cylinder but check on the cylinder attaching and exhaust nuts. If they become loose or rusty the ground conductivity path to the case is reduced thus affecting the EGT and CHT readings.If you have an incandescent landing light the #2 EGT reading is likely to increase when turned on together with the pitot heat.One way of reducing the induced generator spikes (engine vibration) and offset you see on the plot is by connecting the generator/alternator case directly to the airframe instead of relying on the engine case.José

Thanks Jose, we're going to test it out on our next flight.

[KyleKJ90]

Dave

The plot offset on#2 is consistent with a voltage bias induced by the alternator/generator charging when RPM is increased at 00:10 on take off and decreased at 00:42 when RPM is decreased on landing. Notice that the offset is the same (119F) when running ROP during the climb (high RPM)or when leaning at 00:23. I don't think there is something wrong with the cylinder but check on the cylinder attaching and exhaust nuts. If they become loose or rusty the ground conductivity path to the case is reduced thus affecting the EGT and CHT readings.

If you have an incandescent landing light the #2 EGT reading is likely to increase when turned on together with the pitot heat.

One way of reducing the induced generator spikes (engine vibration) and offset you see on the plot is by connecting the generator/alternator case directly to the airframe instead of relying on the engine case.

José

 

Friday I had the opportunity to test this theory of an alternator induced voltage in flight. I can definitively say that's not our issue as pulling the alternator field CB many different times didn't affect the CHT or EGT of the #2 cylinder and the JPI data shows the voltage going down to 0. I just don't see how your theory could be correct here Jose. I'm sorry if it seems rude, but I feel like we're beating a dead horse with that one. =/

 

I checked peak EGT during my flight the other day and #2 was around 1650 degrees. That's nearly 175-200 degrees hotter than the rest peak at. I'm literally going bananas trying to figure this one out. Lycoming says fly it but when the JPI starts blinking "150 DIF" constantly during climb and cruise it's kinda hard to ignore and feel comfortable flying with.

 

My final question to you all. Is it possible that we still might have a fuel issue here? My only reason for asking is because we had Weep No More patch a leak in our fuel tank shortly before this issue began happening. You would think if there was any debris in the tank that it would've gotten filtered out before it got to the flow divider and "plugged the #2 cylinder fuel line" wouldn't you?

[carusoam]

One technical guy says the data looks right but the number itself looks like it is 150° high.

The electronic instrumentation guy tells you how to look for stray voltage sources that would cause the tech guy's observation.

The realist asks have you put a portable thermometer on it to compare the temps after a flight?

A 150°F difference is large enough to leave tracks from start up to shut down...

Best regards,

-a-

[Cruiser]

snip..... You would think if there was any debris in the tank that it would've gotten filtered out before it got to the flow divider and "plugged the #2 cylinder fuel line" wouldn't you?

This is new information that MAY be very important to the resolution of your problem.

IF there was/is debris, it has to go somewhere.

[Piloto]

Dave you indicated a voltage of 0.1. Is this a voltage drop of 0.1 volts?. With the alternator on line you will normally see 14 volts. When the right CB is pulled out the voltage will drop to 12 volts and the voltage warning light will come on and the battery amp meter will show a discharge. I assume your A&P has cleaned the lines and injectors by this time. A source of debris is an old hose connecting the flow divider to the fuel servo. But a true 200F difference will cause engine roughness before you reach LOP. That is why this looks to me like an instrumentation problem rather than a cylinder problem.

José

[Shadrach]

1650 is not a realistic EGT in a normally aspirated IO360. I believe you either have an instrument issue or the combustion event is still happening when the exhaust valve opens.

[KyleKJ90]

Update:

 

I flew her again the other night and our issue still exists with the high EGT on the #2 cylinder so I decided to dive in again this weekend and see what I could find.

 

The day before I gave a call to both JPI and Lycoming. JPI says due to the troubleshooting that we did by swapping EGT probes/leads, we definitely have a hot cylinder. When I asked about an induced voltage being applied to that particular probe/line he once again said that with all the probe swapping we did, it's not a possible cause of our issue. He said the probes are the ungrounded type and when they fail, they tend to do so in such a way as to give either a "colder" indication than usual or no indication at all. I would have to agree that the probes are fine and the cylinder is hot.

 

I followed up that phone call with one to Lycoming and while the tech rep wasn't the most helpful guy in the world, his thoughts stray away from a valve train issue and lean more towards a blocked fuel nozzle/flow divider or an induction leak. I took her apart yesterday and took a look at the screen on the fuel injector body. There didn't appear to be much of anything inside it other than a little tiny bit of fuzz so I cleaned her out and re-installed it. I followed it up with another fuel flow test with the nozzles disconnected (fuel coming straight out of the 1/8 inch stainless lines.) After two minutes of running the boost pump i checked the containers and  there were tiny specs of black stuff in a few of the containers   Although I'm not quite certain where this debris came from my guess might be either residue from old fuel that had boiled in the manifold line, the flow divider or perhaps even the diaphragm from the injector body but I believe the diaphragms in my injector body are the metal kind(due to the OH date). I happened to stumble across this forum which has help shed some light on our issue so I'm off to the airport again this afternoon for some more investigating. I'll let you know how things turn out and until then I'm keeping my fingers crossed!

[Piloto]

As Ross mentioned, a 1650F reading is unrealistic unless the probe is very close to the exhaust flange. This is kind of obvious but is the probe location the same as on the other cylinders. If the cylinder had such a high difference in temperature the engine would not run smooth at peak EGT, specially on a 4 cylinder engine.

Another check you can do is to actually measure the conductivity of the probe leads to the airframe and compare the reading (Ohms) with other cylinders. Get a digital multimeter for this and always use the same point in the airframe (firewall). All the readings should be the same.

José

[KyleKJ90]

Time to get the ball rolling on our EGT issue again. We're almost due for annual and I'd REALLY like to get this thing figured out. I did a cross country flight the other day and burned an asinine amount of fuel with the #2 cylinder leaned to our usual 100 ROP EGT number of 1380. All other cylinders are at or around 1280 and I want to say I was burning 13-14 gallons per hour which is WAY too much for an IO360-A1A. I'm hoping to start on my instrument rating soon but with this high EGT I'm a little hesitant. I'm MORE than convinced that it's not a JPI issue and the EDM 700 is doing exactly what it was designed to do by telling us that we've got a hot exhaust coming from the #2 cylinder. Now, I know this is a stretch but since we have good compression, no burned valves, good cleaned fuel nozzles, plenty of fuel pressure and flow checked fuel flow divider/nozzles, what are your thoughts on a broken oil scraper ring? The JPI data for that flight shows this whole increase of 100 degrees EGT on the #2 cylinder happening in a matter of seconds so SOMETHING must have happened or broken. We haven't done enough flights to determine a high oil consumption yet but if the scraper ring is broken I'm not sure we really want to be flying the thing just to see. The golden question is what makes ONLY the EGT on one cylinder to increase on a lycoming in a matter of seconds like that?

[Piloto]

What power setting you had? 14gph is not unusual at high power settings. Was the fuel flow measured by the EDM 700 or by a separate instrument?

José

[jetdriven]

1280 EGT is target for climb at sea level. That's super rich for cruise. 14-15 GPH is super high, in fact I lean to 16.5 GPH for a sea level air race that's full throttle and 2700 RPM.

[KyleKJ90]

I would agree that 1280 is target for climb at sea level. Typically we're somewhere around there during our climb but not lately. These days #2 is somewhere around 1400 during the climb at 110kts. (Fear not the CHT's are all well below limits.)

 

Typical fuel burn at 100 ROP is about 11.5-12.0GPH for us and we lean the #2 (hottest) cylinder to 1380. That's full throttle, 2500 RPM and 100 ROP. That was then, 14-15 is what we're at now with those same settings. Somethings up and like the topic implies, "It's not the probe"

 

Fuel flow is being measured with the JPI. I flow checked it the other day and believe me, it's spot on. I'm not saying that 14GPH is unusual at high power settings, but for the given power setting above and what we're used to seeing, something is not right here.

[Shadrach]

Go ahead and pull the jug already!!! Inquiring minds want to know.

Seriously though, I doubt that it's a ring, but if all other plausible issues have been checked, what's harm in looking?

[Piloto]

I don't see anything wrong with the cylinder but a temp reading offset as shown on the EGT plot.

 

Check the exhaust gasket on cyl #2 and verify is of the same type as on the other cylinders. Copper gaskets are prone to leak and have different electrical conductivity than the spiral wound type.

 

To eliminate EGT reading instability connect the negative side or case of the alternator/generator via a #10 copper cable directly to the firewall side of the engine ground strap. This was done on later models when digital analyzers were introduced.

 

José

[Super Dave]

I don't see anything wrong with the cylinder but a temp reading offset as shown on the EGT plot.

 

Check the exhaust gasket on cyl #2 and verify is of the same type as on the other cylinders. Copper gaskets are prone to leak and have different electrical conductivity than the spiral wound type.

 

To eliminate EGT reading instability connect the negative side or case of the alternator/generator via a #10 copper cable directly to the firewall side of the engine ground strap. This was done on later models when digital analyzers were introduced.

 

José

 

I agree that it looks like an indication error. We did try pulling the alternator field CB; voltage on the JPI went from a little over 14V down to a little under 13V, but no change in EGT. Also, no change in EGT when switching lights/pitot heat on and off.

[Shadrach]

I agree it looks like an indicator error, but if you have completely swapped the leads and the thermocouples, I don't see how. How does it read when cold?

[Super Dave]

I agree it looks like an indicator error, but if you have completely swapped the leads and the thermocouples, I don't see how. How does it read when cold?

Reads normal cold, at idle, and run up. It's only at inflight power settings that #2 goes high. The higher the power, the bigger the delta.

[Marauder]

I agree that it looks like an indication error. We did try pulling the alternator field CB; voltage on the JPI went from a little over 14V down to a little under 13V, but no change in EGT. Also, no change in EGT when switching lights/pitot heat on and off.

Have you checked the connections on the JPI unit itself? Not sure which of the P connectors are the engine cylinder and EGT temps, but it is possible that you could have a loose connection in the connector itself (vibration with higher power causing a poor connection?).

Also, I believe the leads running from each cylinder has a connector that takes it back up to the monitor through the yellow wire harness. Check that harness all the way back to the monitor. If they didn't sleeve the wiring harness, it is possible that you have worn through and are partially shorting the lead.

I'm not certain what the JPI failure mode is for shorts (didn't read the entire thread and you may uncovered this already), but I would make certain the harness and connector is intact and correct. Changing out the probes with a bad harness would not correct an indication issue.

Sent from my iPad using Tapatalk

[KyleKJ90]

Marauder,

I had the two connectors off when trying to find the JPI download port. Turns out the installer of our JPI wired the download connector by the copilots knees in an easy to reach area. Haha. Wish I would've known sooner but I can confirm that these connectors are attached securely.

I've also looked at all the yellow wires going to the firewall from the exhaust stacks and there doesn't appear to be any signs of chaffing or a damaged wire. Like Shadrach said, by swapping probes and leads I thought we verified that the #2 cylinder EGT is definitely hot for some odd reason. When I talked to the JPI tech rep he said this was correct. His exact woods were, "If you've swapped probes while leaving the channels to their respective cylinder and it didn't change THEN swapped the yellow wires coming from the JPI between the #2 probe and the #4 probe and the #4 indication on the JPI says its higher than the rest, you've got a high EGT. Time to start looking at the engine and talking with your engine tech rep because your JPI is working correctly. "

He said a bad/shorted probe looks like a totally dead/cold cylinder and that our type of EGT probe doesn't use a ground through the exhaust stack. So a bad exhaust gasket isn't the culprit. I must say that I concur.