Is my lambda sensor kaputt? - - Excellence in Motion
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post #1 of 4 (permalink) Old Jun 15th, 2010, 3:44 pm Thread Starter
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Is my lambda sensor kaputt?

Hi all,

I have a rebuilt '97 K1200rs. All seems fine now after I changed the plugs and fixed the ignition timing. However, under constant throttle, I still feel a rocking motion as if the gas input is fluctuating. Have read a few posts on the bucking bronco syndrome but am not convinced my bike is acting like that. At the same time my fuel consumption is way too high. 83 miles on a full tank and the needle is below the 1/4.

When accelerating, there is a lag in the first two gears that I have associated with being too low in the rev range. (Could be wrong here though as I am coming from a single cylinder bike)

Have had people drive behind me to tell me if the bike is smoking on the motorway but it isn't.
When I let the engine idle, I can see the needle go up and down about 100-150rpm and can also hear the difference.

My gut tells me it is the lambda sensor. Is there a way to test the lambda sensor? I have let it idle with the sensor disconnected and then connected and no change. Read the Clymer and BMW manuals and not been any wiser. Short of going to the dealer for a Moditec run which will have be in 2 weeks time, is there any other thing I can do?

Tempted to just do a full run with the lambda sensor out to see if things are different. Would that cause any damage?

Battery is brand new and terminals are tight.


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post #2 of 4 (permalink) Old Jun 15th, 2010, 3:57 pm
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Laqmbda sensor isn't easy to test. Dealer computer can do it. If the bike has more than 25-30 K why not swap it for a Bosch Universal? They'll charge you more for diagnostics.

After that you may still be looking at diagnostics, but at least there's one less thing to worry about.

Running for lots of miles without an O2 sensor may damage the CAT, but you probably aren't too worried about that.

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post #3 of 4 (permalink) Old Jun 19th, 2010, 11:25 am
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I'm not that savvy about K bikes (yet), but I have had others for many years.

On older bikes I always check for vacuum leaks when they act funny. Rubber seals become shrunken hard and cracked over the years and don't seal well.

I can't tell you where to look though.

Good luck.

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post #4 of 4 (permalink) Old Jun 20th, 2010, 3:30 am
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On newer Efi electronic bikes 'fly by wire' you have to develop a new mindset:

Because the Efi system is an electronic feedback loop, you can't always see the obvious, which can sometimes involve a lot of work and you risk breaking other expensive parts. You can be clutching at straws wondering about this or that and since most may not have met an O2 sensor before, that's the item they may want to blame first for problems. It's rather like the old mentality of replacing spark plugs first when something is wrong.

A diagnostic checkup done by a competent tech. at a dealer is more likely to find out what may be wrong before spending money on parts which could be ok. Even then, the checkup can give a picture of what is not in expected range, but there is no guarantee that the tech. getting the diags feedback will know how this connects to a particular fault. At the minimum, the O2 sensor, all the temperature sensors, timing, fans, air temp sensor and TPS will be checked and that would take a long time if you tried testing manually yourself, assuming you knew how to do it and what to expect.

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