Which sensor could have gone?

[Windmill John]

HI Guys,
My 850GS suddenly between fills has dropped 25 miles per tank.
It had dropped when it was in the workshop for a new Hall sensor, when they fitted new injectors. They had taken the throttle bodies off.
Following some great threads, I reset my TPS and improved my fuel use.
This time, it's dropped too quickly. What could cause this?
Power is good.
Could a sensor have gone?
Any help please.
Cheers

 

[sockpuppet]

First I'd check things like the air filter etc. Make sure nothing on the wheels are binding first.

 

[Trullion]

When my 850 GS ran rich it was mainly the TPS voltage, though the potentiometer (pot) was not working as adjusting it made no difference - cured by a used one from Motorworks. Also I replaced the oil temperature sensor, which did not have the range (in ohms) that the replacement one did. As has been said, it could be a clogged air filter. Is there a fuel leak? If it's running rich this will show in the colour of the spark plugs (i.e. they will be sooty). If the plugs look normal maybe you have a small leak. It could also be the air temperature sensor, though I doubt it as I don't believe it has a huge effect, having once forgotten to re-connect mine after an air filter change with no obvious ill-effect.

I think that after the air filter I'd check the TPS voltage first - it's easy enough to do. The only other point I would make is that the mpg on mine, the 1100 and my car varies quite a lot according to ambient temperature. I've kept a spreadsheet since last summer (anal I know) when fuel costs were sky high. In each case the lower temperatures seem to cause significantly higher fuel consumption; a more pronounced effect than how I use the vehicle. Do they add more ethanol to petrol in the winter months, I wonder? I spent a miserable week commuting at the legal limit only to find a 2mpg improvement over my usual thrash the nuts off it (the 850 this is) style.

Let us know how you get on. By the way, mine only does about 48 -54mpg anyway, if that helps.

 

[Windmill John]

Cheers guys,
The only thing that could be binding is the nail I found this morning in the rear tyre!
I'll do some checks, but I did set my TPS 3 months ago.
I cannot remember my fuel consumption, but I usually get 200 to 211 miles to the reserve light, yesterday, I got 174!!
I'll keep you informed.
Is it possible to check the CO2 sensor? where is it? How do I check it?

 

[sockpuppet]

Is it possible to check the CO2 sensor?

The lamda sensor is in the y piece I think.

 

[hops]

the 1100

has it just in front of the 'cat' Item 6 on the diagram, I imagine 850 is the same.

 

[Trullion]

If your bike is like my 850GS it doesn't have one, hence my earlier reference to the 'pot'. This is located on the RHS rear, near the rear seat area. You will find a hole in the rear bodywork, through which you use a flat-bladed screwdriver (pointing upwards) to adjust the pot. You only need to adjust it in very small increments and then wait for each adjustment to take effect - you do this while the engine is warm and ticking over. You should stick an exhaust analyser up the exhaust to set it correctly - I just adjust mine to get it running best. Sorry, but I don't know what the setting should be, nor can I recall which way richens and which way weakens the pilot mixture; others will no doubt advise. If yours does have a lambda sensor please ignore all the above - but I think I'm right in a saying that the UK 850GSs don't. FWIW neither does my 1100RS. Neither has a cat, so they don't need the lambda sensor, or a Motronic code plug. Neither bike surges.

Regards

 

[motobiker]

has it just in front of the 'cat' Item 6 on the diagram, I imagine 850 is the same.

UK spec 1100s (and I believe the 850) didn't have either a cat or an O2 sensor as per that diagram.

The diagram as above is either an American or German (or other european) exhaust its most definitely not for the UK.

Is johns 850 an import? because if it isn't then all this talk of the CAT/Lamda sensor is nothing more than a red herring.