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Thread: Misfire when engine very hot, error 13 - Rear O2 Sensor always lean

  1. #21
    Senior Member 34nineteen's Avatar
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    Electronics can break down, and maybe you did have a coil getting weak. Did you test the values across the terminals to see if it measured within spec? This is helpful info to have, as I've been noticing more people than usual with bad coils. Coincidence? or maybe the coils start getting flakey after 10-15 years. We've been noticing fuel pumps have been causing problems lately as well, so maybe coils are on their last legs at this point.

    unless you've disabled closed loop, the AFV should be "correcting" itself, unless you have a out of spec O2 (or other) sensor providing false readings to the ECM. These can be tricky to ferret out, especially when a part is functional enough to work, yet malfunctioning just enough to cause a problem.

  2. #22
    Junior Member llama's Avatar
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    Quote Originally Posted by 34nineteen View Post
    Did you test the values across the terminals to see if it measured within spec? This is helpful info to have, as I've been noticing more people than usual with bad coils. Coincidence? or maybe the coils start getting flakey after 10-15 years.
    Yes I did measure the resistance and it was out of spec - primary measured 1.1 ohms (should be 0.5~0.7) and secondary measured 12k ohms (should be 5.5 to 7.5k ohms). I measured the new one when it arrived out of interest and it was bang on spec (0.7 and 6.5k). My bike is 13 years old at this point, 100,000km on it.

    unless you've disabled closed loop, the AFV should be "correcting" itself, unless you have a out of spec O2 (or other) sensor providing false readings to the ECM. These can be tricky to ferret out, especially when a part is functional enough to work, yet malfunctioning just enough to cause a problem.
    I didn't think about it learning, but you're right of course it would while in closed loop. I haven't touched the ECM other than reading fault codes and live data. I did change the O2 sensor to a Bosch unit from Amazon while I had the engine rotated, hopefully that's not causing issues (it was suspiciously cheap!). I'll leave it a while and just keep my eye on it, I've only ridden it about 700km since fitting the new coil. According to the seat-of-the-pants-O-meter the bike is running fine, nice clean power through the rev range, so it doesn't feel like I'm chasing a fault at this stage.

  3. #23
    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by llama View Post
    I did change the O2 sensor to a Bosch unit from Amazon while I had the engine rotated,
    Oh yeah, youre that guy.

    I am running a new Bosch O2 also. If I have any issues or weirdness, I'll report back.

    On its mine's maiden voyage, I realized I had leaky fuel pump o rings. Those should arrive today or tomorrow, so I should have it sorted soon.

    Pro tip: do as I say, not as I do. LOL!

  4. #24
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    Llama, you are close to sea level correct? Since I started requiring people include their AFV with requests for tune files I have found that a vast majority of bikes are in the 85-90% AFV range at or near sea level. Many others have AFV of 120 or more and aren't aware of how dangerous this is to the engine. I need to update my website to say that AFV should be within 5% of 100 AFV at sea level. In reality, the only reason the AFV should go down is due to air pressure changes. No engine requires significantly less fuel as it ages, but that's what is happening to these bikes. No, an O2 sensor can't compensate for engine wear. In fact, the opposite happens. If you have the correct tune on your ECM you can configure it for open loop with the AFV at about 103-105 to start with to see how it runs. The O2 sensor is still active to warn you if the engine develops a lean condition, so this is perfectly safe. It is absolutely free to try and only takes about 2 minutes. You can then have CL and OL versions of your tune saved on your phone. If nothing else this will be a good diagnostic exercise.

    BTW, two live data channels I suggest you look at are warm up enrichment (WUE), Intake air temp correction (IAT Corr). When the engine is fully warmed up these should be close to 100. If they are, that means that your engine and air temp sensors are working normally. There are only a handful of sensors so the process of elimination doesn't take long.



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