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Thread: A sort of "resonance" at around 3800-4000 rpm, 2009 roadster

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    A sort of "resonance" at around 3800-4000 rpm, 2009 roadster

    In 6th gear, when the engine speed is steady at around 3800-4000 rpm (around 70 mph), I can feels a sort of rhythmic resonant buzzing coming from the engine. I feel it through the pegs and seat? not through the handlebars, and the mirrors do not vibrate with it. Above and below that speed, it disappears. It is not noticed when in other gears, or when coasting at that speed. Any road defects or wind buffeting and the "resonance" is not noticeable. The frequency of the "resonance" is about 70/min.

    I am thinking that this is probably a normal thing??? just related to the confluence of gear and engine speed, but just thought I'd ask. 2009 r1200r, 25 k miles. I did not notice it until a recent trip.
    It is noticeable enough that I can tell when I am at 3800 rpm just from the feel, ie, do not have to look at the tach

    Thanks

    John

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    Registered User liv2ride's Avatar
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    When is the last time the throttle bodies were synchronized?

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    Touring Rider
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    3800 in any gear, or just 6th? You sure it's not worn tires that do this at 70mph?
    Gary
    Casa Grande, AZ
    2011 R1200RT

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    Thanks for the responses.

    Yes, just in 6th as far as I can tell. I tried to reproduce in other gears...no go, and I tried pulling in the clutch and revving the engine to 3800 while coasting at 70, but couldn't quite pull that off reliably
    Could be either, TBs or tires, or something else. My original thought was road surface, but I noticed it across multiple states with varying road surfaces.
    I thought about the TBs, and will check them, but I thought it may not be them because power was smooth, mileage was good, still I planned on checking--bought some stiffer vacuum hose for my homemade manometer yesterday and will check that. They were last done about 7k miles ago, like early April.
    Re tires.
    Running Pirelli Scorpion Trails. This was noticed on a recent trip, 6500 miles. Tires were almost new at the start, but are close to done now. The good news, the stuck far better than PR3s, the bad, they don't last near as long as PR3s.
    So they are worn, but I noticed it when the tires had maybe 3500 to 4k on them and it did not get worse as mileage accrued. I also thought it could be balance, or road surface, but the resonance disappears when I pull in the clutch and the the engine idles at speed.

    And again, it is often subtle, though noticeable, as long as wind buffeting or poor road surface or something else doesn't overwhelm it.


    When I got home from the trip, I drained the engine, tranny, and FD oils, changed the oil filter...nothing metal appeared when I filtered the oils or on any magnet, but I did see some gritty. sand like stuff in the pans---I think that was my bad and the pans had that stuff before I drained. I did ride through a few dust/sand storms through NM. Need to check air filter. If it's clogged, maybe it let some of that grit get through?
    I didn't see any unusual wear on the tires, like a chunk missing or separation, but will look again.

    Yes, I agree the culprits likely are TBs or tires, or it's something normal that I just didn't notice before on bumpy Louisiana roads
    Thanks again
    John

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    A bozo on the bus deilenberger's Avatar
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    Hi John,

    Just a thought. If you have a GS-911 (or a friend or mechanic who does) - connect it up, and watch the behavior of the O2 sensors (on the real time plotting chart.)

    I had a similar resonance with my '07 fairly early on, and found that one O2 sensor was dead. My periodic resonance was felt most in 5th gear at around 65-75 MPH, on smooth pavement, continuous speed. I tracked down a fault in the wiring going to the O2 sensor and fixed it - and the resonance went away. The fault was caused by the wire routing to the port side cylinder (#2 in BMW talk), where the wire ran and rubbed against the back of the transmission, eventually causing a fault/short. Insulating it, putting some plastic sheathing on it, and then re-routing it a bit seems to have been the long term fix.

    A failed O2 sensor can also cause the intermittent really crappy idle that the hexheads can sometimes experience. Mine has been doing this on and off for about 20k miles.. did everything to smooth the idle out, and when it did idle correctly it was wonderful. When it didn't - it felt like it was idling on one cylinder. The starboard side O2 sensor had failed, again caught with the GS-911. Luckily I had spares on hand, so it was a 10 minute fix once I tracked it down. It's been idling wonderfully since.

    As I said - just a thought, but a scan of the ECU and the live outputs from the engine with a GS-911 might well turn up a pointing finger for you...
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

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    Hi, Don, thanks

    I have to bring her in for a new alt belt-your experience scared me away from doing it myself-- and I want to have the "brake bleed test" performed, as that was part of the 12k service that the prev owner did not do.

    My idle is smooth, but your history of resonance sounds familier. No access to GS911, but I suppose their computer would pick it up also??

    John

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    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by JayElDee View Post
    Hi, Don, thanks

    I have to bring her in for a new alt belt-your experience scared me away from doing it myself-- and I want to have the "brake bleed test" performed, as that was part of the 12k service that the prev owner did not do.

    My idle is smooth, but your history of resonance sounds familier. No access to GS911, but I suppose their computer would pick it up also??

    John
    I'm not so sure their computer will tell them about it or not. I'm not familiar enough with it. There is no fault code set in the ECU when the O2 sensor fails, so if the software they use is the usual dumbed down "tell them what to replace" stuff most manufacturers make for dealer mechanics - chances are, it won't. The GS911 has a specific O2 sensor plotting function that is very useful if you have any idea how an O2 sensor output should look. It will let you spot bad or slow O2 sensors easily. Highly recommended.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

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    Can you pull the sensor and look at it to tell if it's functioning well?. Haynes talks of colored residue with malfunction.

    GS911 is Windows only, I think?? I have macs

    In the Haynes manual it says the dealer computer can tell, but you say it cannot?

    I looked at the wires and the plug connection and that looks fine, no visible wearing of insulation

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    If you plan to ride in dust it is a good idea to put a bit of grease on the air filter gasket to ensure it doesn't bypass at the edges....
    Also, many folks are sloppy removing dirty air filters which can let dirt accumulated at the edge get pushed further into the intake when a new filter is put it- should always clean the air filter area carefully when changing..
    An intact filter won't pass any significant amount of large visibly gritty particles but one that is bypassing or has a few pinholes can pass a surprisingly large amount if you ride into a dust storm...

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    Hey, racer7, interesting that you say that.

    Prior to noticing this "resonance" I DID ride through a LOT of blowing dust and sand. Maybe a hundred miles of it in NW New Mexico along 491.

    When I got back, I changed all my oils , oil filter, and air filter. The air filter wasn't as dirty as I thought it would be, but was still pretty dingy. Are you saying that could have something to do with the resonance? Or are you responding to the gritty stuff in the drained oil pan? I think that grit may have been in the pan prior to the draining. I usually use a clean pan, but may have slipped up this time.

    FYI, when I left I had a new filter in place and I always clean out the box and tube. Grease on the gasket is a good idea and that will happen next time

    Thanks

    John

  11. #11
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by deilenberger View Post
    Hi John,

    Just a thought. If you have a GS-911 (or a friend or mechanic who does) - connect it up, and watch the behavior of the O2 sensors (on the real time plotting chart.)

    I had a similar resonance with my '07 fairly early on, and found that one O2 sensor was dead. My periodic resonance was felt most in 5th gear at around 65-75 MPH, on smooth pavement, continuous speed. I tracked down a fault in the wiring going to the O2 sensor and fixed it - and the resonance went away. The fault was caused by the wire routing to the port side cylinder (#2 in BMW talk), where the wire ran and rubbed against the back of the transmission, eventually causing a fault/short. Insulating it, putting some plastic sheathing on it, and then re-routing it a bit seems to have been the long term fix.

    A failed O2 sensor can also cause the intermittent really crappy idle that the hexheads can sometimes experience. Mine has been doing this on and off for about 20k miles.. did everything to smooth the idle out, and when it did idle correctly it was wonderful. When it didn't - it felt like it was idling on one cylinder. The starboard side O2 sensor had failed, again caught with the GS-911. Luckily I had spares on hand, so it was a 10 minute fix once I tracked it down. It's been idling wonderfully since.

    As I said - just a thought, but a scan of the ECU and the live outputs from the engine with a GS-911 might well turn up a pointing finger for you...
    Don, That's a very interesting input. Because I wanted to get an idea how the BMSK manages dual O2 sensors I had a friend try running with one O2 disconnected. Here's that story: http://www.bmwmoa.org/forum/showthre...l=1#post880803.

    Here's one of the plots. With a dead O2 things really go out of whack.

  12. #12
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by Roger 04 RT View Post
    Don, That's a very interesting input. Because I wanted to get an idea how the BMSK manages dual O2 sensors I had a friend try running with one O2 disconnected. Here's that story: http://www.bmwmoa.org/forum/showthre...l=1#post880803.

    Here's one of the plots. With a dead O2 things really go out of whack.
    Fascinating thread, thanks for pointing me to it..

    I believe if I understood what was found - on initial failure of the O2 sensor the BMSK sets the dead cylinder to a default map which tends to a rich mixture (and things are out of whack...) If the O2 sensor remains dead, after some period of time (a fairly long time actually) - the BMSK then starts moving the mixture setting on the cylinder with no O2 sensor toward the mixture running on the cylinder with an active O2 sensor. That might explain why the R1200R still seemed to be running well, except at idle - with the dead O2 sensor.

    One notable thing now - the engine is extraordinarily buzz free, particularly at 3,700-4,700 RPM, which is my favorite highway cruise RPM. I can feel no buzz at all now through the bars at those speeds and the mirrors are basically crystal clear.

    What's also interesting - there is no stored error code that I could find indicating the O2 sensor was kaput. Unlike OBD-II which would alert an auto driver immediately on failure of an O2 sensor, apparently BMW doesn't want us bothering them or their dealers with trivial matters like that.. What that means is I'll continue to carry the GS-911 on any longer trip (where I take my netbook I use with it anyway).. knowing that a replacement O2 sensor (Bosch universal 4-wire) is only around $60 or so at any decent auto parts store (and I can splice well enough to get it working..)
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

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