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Thread: Intermittent CHT-1

  1. #1
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    Default Intermittent CHT-1

    I have an intermittent problem with CHT-1. See attached plot. Has anyone else experienced this with an EX-3 or FX-3?

    I'm assuming the erratic reading could be caused by a bad sensor, bad wiring between sensor and GEA 24, or by the GEA 24 itself.

    Unfortunately the problem was not seen during fly off and only showed up on the flight home.

    Any tips?

    Andy
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  2. #2
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    Default Re: Intermittent CHT-1

    Andy, I'd bet a dime to a doughnut it's just the connection of the probe. You can probably just pull the "shark vent" off that right side and get to that front, cyl #1 probe easy enough without even removing the cowl. Coming off the probe itself (it's on the bottom of the cylinder pointing upward) the wires should be covered with a fireproof sleeve and be covering the joint where it connects with the wires coming through the firewall. It "should" have a loop in that wire but may not. It's not far from the probe....maybe 6" or so and you may need to remove that sleeve to get to the connection. I always use the round "barrel" connectors but they may not at the factory. The wires from the GEA unit are VERY small (like 22 ga) so if not secured really well they can vibrate and break or come loose. Just check that connection and that is most likely it.

    Look at my post #85 on this page and you can see what I'm talking about with pics. http://forum.cubcrafters.com/showthr...light=ex3+tips

    Also, please come back and let us know what you find in the end.

    Thanks

    Quote Originally Posted by Andy View Post
    I have an intermittent problem with CHT-1. See attached plot. Has anyone else experienced this with an EX-3 or FX-3?

    I'm assuming the erratic reading could be caused by a bad sensor, bad wiring between sensor and GEA 24, or by the GEA 24 itself.

    Unfortunately the problem was not seen during fly off and only showed up on the flight home.

    Any tips?

    Andy
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

  3. #3
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    Default Re: Intermittent CHT-1

    Quote Originally Posted by Daveembry View Post
    Andy, I'd bet a dime to a doughnut it's just the connection of the probe.
    I looked though the data for previous flights and found CHT-1 was clean for the factory tests flights and for the delivery flight. It started to go bad sometime during my fly-off but I had not realized there was a problem. It seems to get progressively worse which would be consistent with a deteriorating probe lead connection.

    The Alcor probe data seems to indicate the probe connection is made by ring terminals. Why do you say barrel connectors?

    https://alcorinc.com/index.php/produ...ouple-bayonet/

    Andy

  4. #4
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    Default Re: Intermittent CHT-1

    Yeah, that’s what i said and they are not connected with ring connectors. You cut them off to connect them with the small GEA wires Look at the forum post I gave you the link to and you will see.

    Quote Originally Posted by Andy View Post
    I looked though the data for previous flights and found CHT-1 was clean for the factory tests flights and for the delivery flight. It started to go bad sometime during my fly-off but I had not realized there was a problem. It seems to get progressively worse which would be consistent with a deteriorating probe lead connection.

    The Alcor probe data seems to indicate the probe connection is made by ring terminals. Why do you say barrel connectors?

    https://alcorinc.com/index.php/produ...ouple-bayonet/

    Andy
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

  5. #5
    Junior Member Bill Tew's Avatar
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    Default Re: Intermittent CHT-1

    Quote Originally Posted by Daveembry View Post
    Yeah, that’s what i said and they are not connected with ring connectors. You cut them off to connect them with the small GEA wires Look at the forum post I gave you the link to and you will see.
    I had a similar issue with a CHT probe on my EX-2 last fall. Problem was with the connections to probe wiring. Reseated the wires in the barrel connectors and problem solved.

    Bill

  6. #6
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    Default Re: Intermittent CHT-1

    Yep.....I think it happens quite a bit. I use to always put good heat shrink over that entire connection where the barrel connector is but now I started reinforcing it by cutting pieces of big tie wraps and making a “splint” on either side of the barrel connector before installing and shrinking the heat shrink. I also started doing that on the center ignition wires where they connect to the 90 degree spade connectors. Same thing there, very thin wires going into that crimp connector and always problems with it breaking with the engine vibration.

    Quote Originally Posted by Bill Tew View Post
    I had a similar issue with a CHT probe on my EX-2 last fall. Problem was with the connections to probe wiring. Reseated the wires in the barrel connectors and problem solved.

    Bill
    Dave Embry
    "You only live once.......but if you do it right.........once is enough."..

  7. #7
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    Default Re: Intermittent CHT-1

    I was able to see the CHT-1 probe and trace the wiring after removing the right side lower cowling louver. The connection between the probe leads and the thin wires that pass through the firewall is made by insulated blade connectors, not the barrel connectors used on the EX airplanes.

    The connection point is very awkward to get at and I decided not to disturb it until I have made measurements at the GEA connector.

    Andy

  8. #8
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    Default Re: Intermittent CHT-1

    46 hours flown in 9 days to complete the fly-off and bring it home so not in any big rush to go out to the hangar. I did spend a few minutes seeing what information could be extracted from the data log. I speculated that an intermittent open negative lead on the CHT probe would show up as changes in CHT when the battery current changed. This would be because the return path for the CHT sensor would be through the engine and the fuselage tubes to the battery and the GEA 24 ground. Changing battery current would cause a small change in the voltage induced in the CHT probe return path.

    Sure enough, the data show a strong correlation between CHT-1 and Amps-1 before, during, and after engine start. The battery charge and discharge current is modifying the CHT-1 voltage seen by the GEA 24.

    Andy
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