R11 Motronic Tuning for Anyone!
It's funny; I remember gazing into the R11 manual that first day I brought the bike home and thinking, 'they really don't want us to work on this thing, do they?' For those of you that haven't seen one, find one: its worth a giggle.
As you might imagine, I spent several of our first months together hanging around a lot of BMW dealers, trying to glean any sort of info I could about the new bike. Some wrenches were accomodating, some told me to quit bugging them, but they all seemed to like working on the bike. So I told myself I could do the same thing (ignorance is bliss.....).
Fortunately, I am a member of several electronic mail lists, one of which is dedicated to the care and feeding of the R1100. So while we didn't know everything, we had enough subscribers living in enough different parts of the country to help accumulate knowledge. R11 owners are not unique in this perspective as I've never run across any BMW owner who wasn't willing to share tech information.
I put this resource to the ultimate test last summer. My R11 required a new throttle position sensor and injector cover at delivery, as the parts on the bike appeared to be etched with acid by the mechanic installing the battery during the PDI. The dealer agreed to fix the cosmetic problem, and I returned a few weeks later to have the new parts installed.
The injector cover was no big deal; we just snapped it on. And the throttle position sensor seemed simple as well, just unplug the harness connector, swap the parts, and replug. The mechanic (yes, he was probably the one who spilled the battery acid) judged the idle by ear, pronounced my bike healthy, and off I went.
I disliked the new idle right away, and proceeded to tweak the rotation of the sensor until I got an idle I liked. And I continued to ride around not thinking I was doing anything wrong.
We then had a snap of cold weather in July, and the bike wanted the fast-idle lever on longer and longer in the morning, plus it would occasionally die when coasting into stoplights, even though we had been riding for a long period of time. I was convinced it was the fault of the sensor and not tight valve clearances since I had just inspected them, so I rotated it by ear and re-synched the throttle bodies at idle and 2500rpm until I was completely satisfied.
I continued with the bike tuned this way for most of the summer, but trying to explain this very unscientific tuning method to my Internet friends with similar difficulties proved to be hopeless. We needed a way to do it right, a way that anyone could duplicate.
And thanks to fellow Oilhead Bob Gorman and Gerry at Cal BMW, we can now do it ourselves. Using just a simple digital voltmeter, any R11 owner can adjust their throttle position sensor like the dealer does, maybe even better.
Using the DVM, it is easy to probe the rearmost wire on the four-way plug used on the sensor. Mine had a small rubber donut for moisture protection blocking my path, and fellow Internetter JD Whitaker suggested using a small sewing needle to fit thru the gap between the donut and the wire. Worked like a charm.
I then clipped the positive lead to the sewing needle, the negative lead to a handy footpeg bolt, and it was time: I turned the key on. Starting the bike is not necessary; just turning the key on should produce a voltage reading on the DVM and mine read about 350mV. Gerry from Cal BMW related that the reading should be between 370 and 400mV, so I split the difference and set it to 385mV. I've received a recent recommendation from Cal that says sea level folks should be at 390mV. Keep your hand on the sensor while tightening the set screws because otherwise the sensor will rotate and mess up your setting.
An important note here: if the initial voltage reading is above 400mV, you need to first adjust the setting lower, and then after switching the ignition off, remove the fifth fuse from the left in the fuse box to erase any defaults in the Motronic computer. When the computer sees more than 400mV from the sensor at startup, it defaults to a preset 'rich' setting.
Anyway, I rode the bike around for a while to get it warm and returned home to sync the throttle bodies. I first set them at idle (Cal says that each air screw should sync around 1.0 turns out - I think my left is at 0.75 and my right at 1.25) and then at 2500rpm. My idle now sits around 1100rpm and I am able to turn the fast-idle lever off within blocks of home on cold mornings. Use the procedure published last month in OTL to sync the R1100 throttle bodies.
So if you know you have a good running bike to begin with (good battery voltage, correct timing and valve clearances, etc.) and you are still having idle problems, this may be something worth checking. It only takes a few minutes to inspect, and gee, won't your Airhead friends be impressed with your diagnostic skills?
Thanks to the guys at Cal BMW for this tip.......