Testing Hall sensor in situ. 850GS

[Windmill John]

Hi All,
Is this possible?
3-400 miles ago, my bike started started starting on 1 pot; the 2nd would kick in virtually straight after.
Since then, it is lacking massive power. If your travelling at say 40 MPH and you whack open the throttle, nothing happens. There is a slight almost indiscernable increase in speed. Eventually it will build up, but your now lucky to get 80MPH
The most important fault is that if you are cruising along, it feels as if someone has momentarily killed ignition; like a type of hunting.
I've just ordered some plugs, as mine have done 10k, tappets are good; okay valve clearances for the pedantics
A similar thing happened a year ago, and a local dealer put it down to a Hall sensor; I was £300 lighter afterwards!
I've seen other links to replacing it yourself with a part from an electronics supplier. I'll be honest, I'm a little shy of fitting this part.
If my R80 goes wrong, I know exactly where to look, but my GS is confusing me. It had new injectors last year, fuel filter replaced about 10k ago, covered 72K miles.
Could someone please point me in the right direction.
If Steptoe was closer and it wasn't one of my work transports, I'd drop it off there. But, I do like to try and resolve things.
Cheers Guys.

 

[Nobby]

don't think its the hall sensor i think they work or don;t if you know what i mean i would check fuel filter mine did a similar thing not to long ago and turned out to be a split filter (not enough fuel pressure)but you can ask steptoe he's the god of gs'

 

[Colban]

If the hallsensor was replaced fairly recently,unless there is a connector corrosion problem,i'd say it isn't that.
Engines need compression,fuel and sparks to work.
If you turn the motor over with the plugs on the cylinder heads,can you see a decent spark?.
Water in tank or loose fuel hose clamps (did you fit new clamps when you changed the fuel filter) are common problems here.
Can you measure the compression?.
Hows the air filter?.Possible coil breakdown?.

 

[The smudger]

Injector wiring? Something tells me on the earlier injected boxers the harness's to the injectors were too tight, occasionally causing the wires to break due to the seal being stretched/water getting in corroding the terminals, start there?

 

[Steptoe]

Test the HT leads. Also the TPS.

Seamaster (a forum member) once had an R850GS with a similier sounding problem, lack of power above certain revs, and turned out to be a faulty motronic unit.
But thats extremely unusual, and i only mention it because his bike was also an R850 .

 

[khpossum]

Just as background information: to test hall sensors on the road you could do something as described in the following (I think):

http://www.advrider.com/forums/showthread.php?t=79207

Instead of turning the engine from the front you can also turn the rear wheel while in gear and see if the hall sensor fires (at approximately the right time).

KP

 

[Steptoe]

Just as background information: to test hall sensors on the road you could do something as described in the following (I think):

http://www.advrider.com/forums/showthread.php?t=79207

Instead of turning the engine from the front you can also turn the rear wheel while in gear and see if the hall sensor fires (at approximately the right time).

KP

That method is no good for the example above with an engine starting and running.

The method above also fires the fuel pump. So just listen at the tank instead of removing any of taking parts.

There's also a big BUT when using this method for deciding if the hall sensor hads failed - if the pump DOESN'T prime while turning the engine by hand it definatly is the hall sensor.
But even if the pump does prime doesn't mean 100% it isn't the hall sensor - if you follow

 

[Windmill John]

Testing hall sensor

Cheers Guys,

I'll run through the list and let you know.

John