Erroneous Thermocouple Readings

[Mark_Dickens]

I am in the process of reinstalling my engine after a teardown and all but one of my thermocouples (#3 EGT) are indicating obviously bad temps (as high as 200F+ and as low as 43F), while the plane is just sitting in the hangar. The odds of seven out of eight thermocouples being bad all of a sudden can't be very high, when they previously worked fine. I didn't unplug any of them while the engine was gone. What's the best way to test them to figure out if they are truly bad or if it's just a wiring problem?

 

[Mark_Dickens]

Does Dynon still provide support here?

 

[jakej]

Mark, just a thought here - you most likely don't have a 'box' failure especially as you've just removed/replaced the engine - did you connect the heavy duty ground cable from the engine to the firewall/battery ?
Was the EGT/CHT connector removed from the Dynon or EMS module ?

Jake

 

[Mark_Dickens]

Mark, just a thought here - you most likely don't have a 'box' failure especially as you've just removed/replaced the engine - did you connect the heavy duty ground cable from the engine to the firewall/battery ?
Was the EGT/CHT connector removed from the Dynon or EMS module ?

Jake

Yes, the ground strap is connected to the common ground point which is in turn connected directly to the battery. The oil temp sensor is working normally. I don't think this is a ground problem. And no, none of the EMS connectors were touched.

What I was hoping to get was a way to test each probe with a meter or some way to determine if the probes are good, and therefore the wiring is bad or vice versa. I'd think Dynon has a test process, wouldn't you? What's what I'm after. Thanks for responding!

 

[jakej]

Were the CHT/EGT probes disconnected from the Dynon (brown) harness ?
What are the temps displayed for each probe & cylinder ?
check your pm's.
Jake

 

[Dynon]

Does Dynon still provide support here?

As we note in the forum guidelines, the forum isn't staffed by our technical support team, and it isn't considered an "official" support resource. If you need personalized help, we encourage you to please contact our support team directly. That said, we try to check in on things here a few times a week, and those of us that do reply are generally nerdy long-timers that know a lot of the technical details.

That said, when thermocouples aren't connected, their values "float" and you'll see random numbers. So suspicion number one is that they're somehow not connected to the the EMS module (D25 connector not seated, or something along those lines). One general test to know about is that if you short the two pins of a single thermocouple together (at the D25 connector), you should see ambient temperature.

 

[Mark_Dickens]

As we note in the forum guidelines, the forum isn't staffed by our technical support team, and it isn't considered an "official" support resource. If you need personalized help, we encourage you to please contact our support team directly. That said, we try to check in on things here a few times a week, and those of us that do reply are generally nerdy long-timers that know a lot of the technical details.

That said, when thermocouples aren't connected, their values "float" and you'll see random numbers. So suspicion number one is that they're somehow not connected to the the EMS module (D25 connector not seated, or something along those lines). One general test to know about is that if you short the two pins of a single thermocouple together (at the D25 connector), you should see ambient temperature.

I didn't touch or even get near the EMS box, so while anything is possible, I doubt that's it, but I did reroute and rework the probe wiring firewall forward. I have checked that the spade connectors are tight and they are, but I wonder if all the reworking and rerouting might have resulted in some connection issues. I will remove all of the probes and see what I can find. Thanks for the reply. I did think this was a support resource, so I was mistaken

 

[Dynon]

We do basically try provide light to medium support and advice here as we're able to, but it generally won't be as personalized or immediate as our phone/email systems.

 

[jakej]

"I didn't touch or even get near the EMS box, so while anything is possible, I doubt that's it, but I did reroute and rework the probe wiring firewall forward. I have checked that the spade connectors are tight and they are, but I wonder if all the reworking and rerouting might have resulted in some connection issues. I will remove all of the probes and see what I can find. Thanks for the reply. I did think this was a support resource, so I was mistaken"

Yep, an EAB community assist situation . Not sure if you got my PM (asked about the wiring/connections). Now that you advise there was a lot of reworking & rerouting of the wiring I'd suggest that's where the solution is. Knowing what the readings are for all the probes would help too & that you have doublechecked the colour coding.
Please never be afraid to ask questions, there are many here who have vast knowledge & 'in the field' experience & are willing to share that to achieve a good outcome for you. Also sharing the end result means that you have contributed to the knowledge base so that others can learn & everyone wins.

 

[Mark_Dickens]

An update and a new question. Yes, the data plug from the EMS had gotten loose, probably while I was squirming around in the cabin of my RV-8 doing the annual "tighten the landing gear bolts" routine, so all tightened up and most indications now make sense, but not all.

I have shortened the thermocouple wiring on cylinders 2 and 4 (left side of engine), using barrel splices so that the wires on both sides are compressed together. As I understand and read in multiple places, the length of the leads for the thermocouples doesn't affect the readings, and for the EGT side, indeed this is true. But, the CHT side is reading low, in the order of 100 degrees F on #2 and about 60 degrees on #4. What's strange about this is that all CHT probes read ambient temps just fine, but as the heat goes up, they don't keep up with it. I tested this with boiling water and they indicated 168F when the CHT on the other side of the engine (which has not been altered) read 210F, but obviously there's an issue with the probes that have been modified. I'm trying to figure out what to do about it.

Any ideas?

 

[vlittle]

An update and a new question. Yes, the data plug from the EMS had gotten loose, probably while I was squirming around in the cabin of my RV-8 doing the annual "tighten the landing gear bolts" routine, so all tightened up and most indications now make sense, but not all.

I have shortened the thermocouple wiring on cylinders 2 and 4 (left side of engine), using barrel splices so that the wires on both sides are compressed together. As I understand and read in multiple places, the length of the leads for the thermocouples doesn't affect the readings, and for the EGT side, indeed this is true. But, the CHT side is reading low, in the order of 100 degrees F on #2 and about 60 degrees on #4. What's strange about this is that all CHT probes read ambient temps just fine, but as the heat goes up, they don't keep up with it. I tested this with boiling water and they indicated 168F when the CHT on the other side of the engine (which has not been altered) read 210F, but obviously there's an issue with the probes that have been modified. I'm trying to figure out what to do about it.

Any ideas?

It's important that you do not mix crimp connector brands or types on an individual probe. Also, get rid of any fast-on terminals and use quality barrel splices. Any oxidation in the fast-ons (such as sitting too long) will cause large errors in temperature readings. Until I did this on my Rocket, the temperature readings were all over the place... with brand new probes and wiring.

The voltages being measured on the probes are in the millivolt range. Terminal corrosion can cause error voltages in the same magnitude and there is no appreciable current to 'clean' the contacts.

V

 

[Mark_Dickens]

It's important that you do not mix crimp connector brands or types on an individual probe. Also, get rid of any fast-on terminals and use quality barrel splices. Any oxidation in the fast-ons (such as sitting too long) will cause large errors in temperature readings. Until I did this on my Rocket, the temperature readings were all over the place... with brand new probes and wiring.

The voltages being measured on the probes are in the millivolt range. Terminal corrosion can cause error voltages in the same magnitude and there is no appreciable current to 'clean' the contacts.

V

Thanks. I'm using the EI barrel splices (see part 10-05470 at Spruce). They compress the wires from the thermocouple on top of the wires from the EMS, so I think I'm getting a good connection. They work well with the EGT wires, but the CHT side isn't working that well for some reason. I'm going to try reworking those connections and test with boiling water to see if perhaps there's just a bad connection on the CHT side.