Unusual EGT reading prior to engine start

[geoffreylewis]

I have a D120.
Number 2 EGT reads 1930 degrees upon switch on, others are all at ambient, it reads what I consider to be reasonable after engine start, Is something on its way out?

 

[jakej]

I have given numerous inputs to perceived issues with EGT/Cht, a search should find the answers . Or just PM me.

Jake J
Glasair IIS FT

 

[dynonsupport]

1930 is likely a broken connection or thermocouple probe. First thing to do is swap the connections between your EGT 2 and another probe to see if it follows the wires or the probe. Then check your wiring or replace the EGT depending on what you find.

 

[Roy_Skelton]

I too have unusual EGT and CHT readings before start and after.  Two cyl are normal, and two are flashing red 99, and alternating with "SPN". Can anyone tell me what is going on. I have got it to stop at times, but next time I start it is doing the same.

 

[dynonsupport]

SPN is just the span alert that you have set to warn you two cylinders are more than X degrees apart, which they are going to be if one is -99.

Are you saying you never have issues in the air, only on the ground?

 

[fducharme]

I also have an intermittent problem with EGT and CHT at startup. As soon as I power the EMS on, I'm flooded with a dozen alarms all related to cylinders and exaust temperature. The temperatures reported by the EMS are just crazy (like out of scale, SPAN error, fluctuating impossible values). I noticed that the problem occurs more frequently when the aircraft is cold (parked outside at -10C for example).  After a while, the aircraft warms up and the problem goes away.
Most of the time the engine is started before the EMS is powered on.

 

[Dynon]

Hi Fred - Which exact product of ours is this?

 

[Battson]

I have the full set of Dynon sensor products and I am also experiencing the same issue.  Sometimes, at very low power settings or when I shut down the engine, my #5 EGT shoots way up - to maybe 900*C when the engine is running, or even to 1200*C if shutdown.  At first we suspected a bad plug, before we shutdown, but clearly this isn't real as the engine isn't that hot once it's shut down.

The problem seems to happen spuriously, but seems to be getting worse / more common. So far we have no problems at normal engine operational power settings - this confuses me as a damaged wire is a damaged wire no matter what the throttle is doing....??

I cant see any damage to the wires so far, but will look harder at my 100hr which is coming up fast.  Am I looking for an open circuit or a short circuit??

 

[Dynon]

Shorts won't affect our reading, and generically, any early contact (before the intended tip junction) of the two thermocouple wires will lower the temperature, not raise it. So that's probably not it. An "open" will cause the reading to float around and be random / erratic. So that's not an impossibility. If you were somehow gettting an outside voltage onto either wire, that would cause a spike (but would be more likely to rail out, not just hundreds of degrees). Is it definitely correlated to the engine run speed? Any chance it has to do with electrical load changes as you shut down your electrical system?

Also, one thing to do is to move the probe to another cylinder and see if it moves with the probe or the cylinder, just to make sure you're not seeing an actual temperature spike (granted, 1200C when shutdown doesn't seem likely to be real)

 

[Roger_Lee]

Just a thought,

If you have any header wrap from the exhaust pipe touching the EGT probe that will cause it to fluctuate 100-125F. Been there, done that. Don't over wrap the probe or put the wrap under the probe. I researched this a few years back and no one seems to know exactly why.

 

[Battson]

Is it definitely correlated to the engine run speed? Any chance it has to do with electrical load changes as you shut down your electrical system?

Thanks for your help,

I am not sure it's correlated to engine speed directly, but most probably something else which happens at lower power settings - it has only occurred at lower power settings or after shut-down - so that could be to do with anything...

Some of the thermocouple wires run parallel with alternator and starter power cables. I guess they could easily induce a voltage in the wire, but I am not sure why that would only happen at lower power settings.

 

[Dynon]

What kind of engine is it?

 

[Battson]

IO-540-A4 EXP

 

[Dynon]

The thought there was that if your electrical loads were changing (a Rotax generator, for example, often can't keep up with the aircraft electrical load at low RPM, and so you'd go from having no negligible current going to/from the battery to having a battery discharging), and the current paths that were changing were near that EGT wire, that you could be inducing a voltage in the EGT wire that would look like a spike.

 

[Battson]

After 4 more flights this weekend, the problem didn't reoccur... It seems to be worse on really hot days. Maybe.
A sporadic alarm is the hardest to troubleshoot!! :-/

 

[fducharme]

Hi Fred - Which exact product of ours is this?

I have an EMS-D10. I experience the problem again today and took a video. I notice the problem occurs mainly when the aircraft itself is cold. Today it was -13 Celsius. The weirdest thing, is that shortly after I took the video, while I was taxiing back, the problem suddently went away and the readings were just fine after that. So, the probes are working properly, the wiring looks fine. I do have the latest firmware updates. Any clue?

 

[fducharme]

Here's the link to the video. (could't post it in my last message). See http://www.youtube.com/watch?v=zDc-lzIYM9A

 

[Dynon]

A couple of questions: You're showing the D10A, but is it the same on the EMS/FlightDEK? Just want to rule out a connectivity issue. Also, if you pop off the thermocouple D25 connector off the EMS/FlightDEK, do you get the same crazy high temps? Or do they just float/vary (the latter is what is expected)

 

[fducharme]

The data is coming from an EMS D10 witch is in front of the copilot. It was easier to film the EFIS D10A since it was in front of me. Anyway, the EMS D10 was showing the exact same readings. If I disconnect the thermocouple connector, I see crazy varying temperatures for about 2 seconds, then they all drop to a steady 55F +- 3F witch correspond to the ambient temperature. So basically, without any thermocouple I get a good reading and when I connect the thermocouples, I get varying crazy temperatures like 500F on CHT #1, 750F on #2, 550F on #3 and 720F on #4. This test was done with the engine turned OFF. If I start the engine, I get the same crazy values but just a bit higher.

 

[fducharme]

For those who are interested, I sent my unit back to Dynon. They found a "hardware" problem and resolved it. They shipped my unit back the next day. I reinstalled it, and everything is ok now.