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Sensor wires

wirejock

Well Known Member
How did you all secure all those EGT and CHT wires from where the come off the cylinders back toward the firewall?
 
Just me

Here is how i did it.
It has changed slightly once I added the baffles; basically the rear mount went to the baffle instead of the cylinder.
I kept the spark plug wires separated from the sensor wires.
 

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Sleeve

Here is how i did it.
It has changed slightly once I added the baffles; basically the rear mount went to the baffle instead of the cylinder.
I kept the spark plug wires separated from the sensor wires.

Is that heat shrink with fire sleeve over it?
 
I copy-catted a bunch of other builders and just ran them along with the plug wires, securing with adel clamps and lace where practical. You can also see the alt. air door actuator cable routed and secured separately. The black material is anti-chafe sleeve that came with the CHT and EGT probe kits.

 
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I did it pretty much like John S did it...just maybe not that nice. Make sure you don't introduce a kink in any of cables. They're subject to a lot of vibration, which makes them prone to eventual breaks in the bending point.

And Wirejock, that sleeve is likely the fiberglass wrap that came with the sensors to protect and insulate the connection points.
 
I copy-catted a bunch of other builders and just ran them along with the plug wires, securing with adel clamps and lace where practical. You can also see the alt. air door actuator cable routed and secured separately. The black material is anti-chafe sleeve that came with the CHT and EGT probe kits.


The EMI from the plug wires can create havoc for the thermocouples. Suggest giving them some spacing. Seen it happen a couple of times and providing more clearance resolved the issue. I suspect the shielding is helping as both times it was on auto style unshielded wire.
 
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The EMI from the plug wires can create havoc for the thermocouples. Suggest giving them some spacing. Seen it happen a couple of times and providing more clearance resolved the issue. I suspect the shielding is helping as both times it was on auto style unshielded wire.

Interesting, thanks! Didn't realize there was a reason to not run them together. Good project for my next condition inspection.
 
This is one location that access really counts. There will be maintenance needed on just about everything that is bolted to the motor. They fall into two categories, Maybe and for sure.

Maybe.... least likely first.. Sump. Accessory case. Cylinders.

For sure... Everything else. including.. Spark plugs, Oil filter, Sump screen, Air filter, Mags, Timing mags, Fuel pump, Rocker cover, intake, and exhaust gaskets. All oil and fuel lines, and all spark plug wires.

Think about how you are going to change an oil filter or change a mag. Keep the area clear of unneeded wires and hoses. The motor mount tubes are already in the way, use them for wire and hose runs.

If you are going to maintain your RV, you will thank yourself in the future. If you are sending your RV to a mechanic, his job is made easier, quicker... $$$ saved.

Plan your routing to avoid conflict. And for wire retainers, consider pull ties. They are cheap, simple to install, easy to maintain, and easy to update when a wire needs to be added. Be sure to trim the tail flush to avoid future cuts.

These two pictures are wired with 4 egt's and 4 cht's. Not one of the eight wires are in the way of anything except the sump... and it's least likely to be removed. And if it needs to, I just cut a few pull ties and the wires are removed.
20220822_124244.jpg20220822_124223.jpg
 
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I ran my CHT and EGT wires the same as most of the pictures. I saw other flying RVs using the same setup at the airport without any issue.

I suspect the CHT and EGT are jut analog thermocouples. The provide the resistance values base on the temperature change. These are not "data" cables sending bits or pulses over the wires so they are not susceptible by EMI interference since there is no data to be interfered or corrupted. Just my 2 cents.
 
I kept my spark plug wires and sensor wires separated also. I made small drop down tabs/adel clamps to secure the sensor wire separately.

B006681C-3C6B-44AB-A518-6FCF47D61251.jpg
 
I ran my CHT and EGT wires the same as most of the pictures. I saw other flying RVs using the same setup at the airport without any issue.

I suspect the CHT and EGT are jut analog thermocouples. The provide the resistance values base on the temperature change. These are not "data" cables sending bits or pulses over the wires so they are not susceptible by EMI interference since there is no data to be interfered or corrupted. Just my 2 cents.

Thermocouples are not resistive sensors like many others on the engine are. Thermocouples produce varying levels of micro voltage based upon temp and the instrument reads that voltage (VERY low levels). I can confirm that at least two installations have seen fluctuating temps that went away by adding more space from plug wire. Both were std auto plug wires (unshielded) and as I mentioned, I believe that the shielding on the mag harnesses is bleeding off the EMI, so no issue. However EI users should not assume this will work universally for them, as std auto plug wires have no shielding. Normal sensors are having many volts pushed through the circuit, whereas the thermocouples are seeing 10ths or 100ths of volts in the circuit, so much less immune from EMI.

You are probably thinking of a thermistor, which is a resistive sensor, but is nothing like a thermocouple that produces it's own electricity for the instrument to read. As you can imagine, the electricity produced simply by two differing composition wires in contact is extremely low power and therefore sensitive to outside forces. Your alternator is nothing more than a spinning magnet (electricity actually is creating the magnetic field here) and it powers the whole plane. Magnetic force is electrical energy, and vice versa, and when the coil's primary winding opens, 10's of 1000's of volts are created, producing a considerable magnetic field.

Many thermocouples also have shielding specifically to eliminate this issue. Unfortunately most of the stuff we use is unshielded thermocouple wire.
 
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Another Option

I made some straps from scrap that enabled the use of Adels. Wires are separated for future maintenance purposes, primarily.

Ron B.

Firewall Forward.jpg
 
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