Is RPM fluctuation the same as surge ?

[happy wanderer]

Thanks for the feedback. When the bike was dried out this morning it was running fine. I'm going to get the hall sensor replaced and see pray that's the problem. It doesn't rain too much here in Southern TX, so it may be a while before I can figure out if it worked or not

In the meantime, you can try Paul Glaves roadside emergency HES wet harness fix. I think it goes something like this (from memory)
Carry a can of WD40. If she fizzles out in the rain, pull the tank off to get at the connector for the HES. Pull it apart and spray a whole bunch of WD40 down the wiring harness. Gravity will help it run down in there and chase the water out. Might just get you home!

 

[Detroit Kim]

DK, how you describe "RPM fluctuation" does not sound to me like how most people describe "surging". Surging, if it is noticable at all, generally happens when you are trying to hold a steady speed with a very small throttle opening. Like cruising the Interstate below the speed limit at, say, 3000 RPM or so. Could also happen at a constant low speed in 5th/6th gear. As soon as the RPMs get above 4500 or so, or if you just wack open the throttle, all hint of surging should disappear.

Good luck

No, I think its the same. Constant throttle, with flutuating revs.
I'm trying to check the air temp, humity, air pressure and brand of gas each time I ride. Because its sometimes not as bad as others.
I like the idea of the ECU piggy back. Anyone have any experience with it ?
Has anyone had an official explanation from BMW NA ? I'm sure if it was one of their cars, they would have found a fix by now.

 

[jduke]

Surging has been a problem from the first oilheads. It used to be identified as occurring at about 4200 rpm in high gear at a steady throttle. Almost like the computer is "hunting" for the ideal fuel mixture.

 

[nrpetersen]

My theory:

I think surging is caused by one cylinder cutting out from too lean mixture. The fuel map for emission reasons is lean (about 14:1 A/F ratio) and it doesn't take much further leaning (about 20:1 A/F ratio) to make a cylinder simply not fire. When you combine that with a processor control that reuires both fuel injector pulses to be the same length, at near closed throttle one cylinder can drop out. All it takes is for the air flow in that cylinder to be modestly greater than the other.

If there is surplus oxygen in the exhaust from either cylinder, the processor quickly calls for further leaning - of both of them.

 

[Cyclepilot]

Explains why the bike runs nice and smooth until it warms up a bit. It's running rich when it is cold.