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Thread: How do I determine if cylinder head temp sensor is bad?

  1. #1
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    How do I determine if cylinder head temp sensor is bad?

    I have had an issue with power dropping out and miss firing once the engine has warmed up. I've logged some data and I'm trying to get my footing reviewing the data with MegaLogViewer. I suspect my ET sensor is not behaving. The temps are very high (I think) 486 degrees F and will swing as much as 60 degrees F in a half a second. There is an apparent correlation in the O2 readings will reads a sustained rich plateau during this period. which I would think indicates a miss fire period. The bike runs fine closed loop. How can I determine the ET sensor is working?

    I've been dealing with this issue for some time now and have replaced the coil, plugs, plug wires, and the TPS. I took it to an HD dealer thinking they would have more experience with this problem. Ended up spending a lot of money and got a new fuel pump, newer new plugs and they re-reset my TPS. I don't think their tech ever road the bike because if he had, in 15 miles he would have realized that he had failed fix anything.

  2. #2
    Senior Member Cooter's Avatar
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    A 60* swing in 1/2 a second? Replace the sensor and double check the wiring isn't chaffed.

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    Thanks Cooter

    I was hoping for a solution that I could verify without rotating the engine, but it is looking unavoidable. One other thing I'm noticing... the ET sensor output is quite noisy and the amplitude of the noise increases to 60* as the temperature increases over the course of the ride. I guess I'll check my ECM ground leads then rotate and replace ET and O2 sensors and see how that goes. Anything else I should consider replacing while I have access?

  4. #4
    Senior Member konarider94's Avatar
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    There is a chart in the manual that gives resistance values for various temperatures, does anyone actually read that thing? It has great troubleshooting guides.

    Let the bike sit so you know its the same temperature as ambient and disconnect the sensor. Check the resistance and see if it correlates with the ambient temperature. I would post the pic but I had it saved in my pics on the old forum. Still bitter about the "upgrade"

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    PRMAYS did you replace the ET sensor? If so did it solve your issue? I am currently having the same issue and have replaced the coil, spark plugs, wires, TPS, and IAT sensor. I know its a long shot considering this post is 6yrs old.

  6. #6
    Senior Member Cooter's Avatar
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    Alternatively you could do what KonaRider posted just above yours... and see if it's a waste of money and time to replace it before you replace it.

    Here is a copy of the manual for you to read instead of continuing to waste cash and time blindfolded fishing.
    http://buellmods.com

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    Thanks Cooter, I already have a 2009 manual and have done some troubleshooting and continue to. I tested the coil and it passed when it was ambient temp. So i heated it up to around 200 degrees considering that seems like when the issues start to happen and it was out of limits per the manual. So I thought the coil was the issue. I try not to blindly replace parts if not necessary. The TPS and IAT were all cheap auto part store replacements so I figured that wouldn't hurt and plugs and wires are maint items. I've done a ton of research on this bike (2009 XB112SCG) and its always helpful searching forums for people that have the same issues/symptoms. Problem is when people figure the issue out they never get back and let everyone know. I also sent the ECM to Tim at IDS to make sure the correct tune is on it and nothing is wrong with the ECM. The ET sensor is a little pricey and I am still in the process of troubleshooting. I looked in the manual and can not find the resistance specs or anything on troubleshooting the sensor. It just says to replace. But if you have a screenshot or any other direction to help that would be much appreciated. Tim told me to ride it and look to see if the temp values spike up or down when above 200 degrees and that a good sign of a bad sensor. I do have a Buelltooth. He also said to log some records and I could send him a file that he can look at. He's been a lot of help.

  8. #8
    Senior Member Barrett's Avatar
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    Romper: The ETS switch dictates most every performance parameter that the ECM controls and operates. Historically, few seem to even understand this. All values for active temps below...factory TSB citing known problem...FC # and causes.

    1- Historical fault code #14 associated with failing ETS switch. The ECM is seeing values it doesn't like.
    2-Dealer "advisement bulletin" December/2004 citing ETS triggering fault code #14 due to wire chafing on rear cylinder rocker cover. You should check for same.
    3-Engine does NOT need to be rotated/lowered to replace ETS. If anyone advised you that's required, they're wrong.
    4-Slotted 1/2" socket required to R&R ETS switch. Purchase or simply make your own.
    5-The factory part # for your 2009 ETS differs from earlier listings only because the connector plug was changed to Delphi style. There is NO known automotive application cross-reference part # I'm aware of, though one may exist.
    Operation.....Values....test procedure below:

    The engine temp sensor is a thermocouple that changes resistance as the temp changes. In this case the resistance goes down as the temp goes up.

    The ECM presents a voltage to the sensor and when it is cold the voltage stays high. As the engine heats up the resistance goes down and the voltage does too. That is how the ECM measures the engine temp.

    VDC DEG F.
    0.00 572
    0.21 491
    0.42 410
    0.62 374
    0.81 338
    1.20 302
    1.59 266
    3.01 185
    4.43 104
    4.63 77
    4.83 50


    5550_20100227042722_L.jpg
    Last edited by Barrett; 05-21-2022 at 11:06 AM.

  9. #9
    Senior Member Cooter's Avatar
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    Fantastic info from Barrett

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    Yes, thanks for the info Barrett. My issue turned out to be the fuel pump. I'm thinking it was the pressure regulator. It had a bunch of junk in it (the screen did also) and after comparing it to the new one it looked jacked up on the inside. Anyways I replaced everything with a kit I bought from Aagaard Moto. Runs like a champ now!



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