I am having problems with EGT and CHT readings on a Jabiru 3300. The CHT on some of the cylinders are 50 degrees C higher than a temporary analoge gauge. I have read some of the previous discussions and have confirmed that the termocouple wiring, probe diamtre and leakage is OK. What else can I do.
CHT problems on Jabiru 3300
- Thread starter Kotie
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- Mar 23, 2005
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The thermocouple inputs on the EMS are pretty solid. I don't know of a case where there was something wrong with the actual EMS in these cases of "incorrect" temperature reports.
Case in point - we recently helped an OEM partner determine that their much more expensive certified EMS that they were checking their Dynon EMS against was much less accurate than the Dynon when they were suspecting the Dynon was giving them CHTs that were too high (it wasn't - in fact it WAS the engine overheating as the Dynon was pointing towards).
Some things to check:
-is there any temperature change across any of the junctions in your thermocouple wire? For example, if you have a junction at the firewall (where there's a temperature change for sure), that's bad, and will cause temperature inaccuracies.
-you can learn a lot about what's going on by moving probes into different ports, and also by connecting different physical probes to different harness leads.
-consider the possibility that you actually do have some temperature variance in your engine that the EMS is correctly reporting. Our EMS does some pretty advanced things, such as cold junction temperature compensation, which in non-technical terms means that our EGT/CHT readings WILL often be different than an analog gauge, but because the analog gauge is simply wrong except under very specific (non-real world) conditions.
Case in point - we recently helped an OEM partner determine that their much more expensive certified EMS that they were checking their Dynon EMS against was much less accurate than the Dynon when they were suspecting the Dynon was giving them CHTs that were too high (it wasn't - in fact it WAS the engine overheating as the Dynon was pointing towards).
Some things to check:
-is there any temperature change across any of the junctions in your thermocouple wire? For example, if you have a junction at the firewall (where there's a temperature change for sure), that's bad, and will cause temperature inaccuracies.
-you can learn a lot about what's going on by moving probes into different ports, and also by connecting different physical probes to different harness leads.
-consider the possibility that you actually do have some temperature variance in your engine that the EMS is correctly reporting. Our EMS does some pretty advanced things, such as cold junction temperature compensation, which in non-technical terms means that our EGT/CHT readings WILL often be different than an analog gauge, but because the analog gauge is simply wrong except under very specific (non-real world) conditions.
DBRV10
Active Member
temporary analogue gauge :-?
Trust the Dynon!
Trust the Dynon!
DBRV10
Active Member
Good Idea.
Just remember to do it at the 320-400F range not at say 80F
Just remember to do it at the 320-400F range not at say 80F
I have done a test on the CHT's by butting the normally highest and normally lowest Dynon probe together with the temporary analog gauge as well as a calibrated thermo-couple. The following data was measured:
Calibrated thermo-couple 95 156 204 degree C
Analog left 100 100 205
Analog Right 100 100 204
Dynon highest 101 164 209
Dynon lowest 101 163 207
This tells me that the dynon probe that is reading high has to be influenced by leakage around the spark plug. The analog guage was placed on the other sparkplug on the same cylinder and it read 50 degrees lower than the dynon. We see no evidence of this. We are going to install another spark plug washer below the probe. What else can we do?
Calibrated thermo-couple 95 156 204 degree C
Analog left 100 100 205
Analog Right 100 100 204
Dynon highest 101 164 209
Dynon lowest 101 163 207
This tells me that the dynon probe that is reading high has to be influenced by leakage around the spark plug. The analog guage was placed on the other sparkplug on the same cylinder and it read 50 degrees lower than the dynon. We see no evidence of this. We are going to install another spark plug washer below the probe. What else can we do?
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If I'm reading your report correctly, it's looking like you've shown that different probes and instruments basically agree with each other, despite the different probes and instrument measurements. So it's looking like an actual temperature differential on the different probes. I'd forgotten that the Jabiru uses the spark plug probes, so leakage could contribue to the difference in those readings.
jakej
Well-Known Member
Here's an interesting developement http://www.youtube.com/watch?v=Li9LiDYGQOQ re the CHT's and Jabby engines - maybe the higher temps issue that some are having will be resolved.
Jake J
Jake J