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Re: TPS voltage

In a message dated 9/7/05 9:59:21 AM Eastern  Standard Time, dr.ben@xxxxxxxxx 
<<The TPS senses and  communicates the butterfly angle to the ECU. It also  
telegraphs the  rider's expectation; I hope somebody who understands  
that better will  enlighten us as to how that is managed by the  ECU.>>

It uses rate-of-change in throttle  position to select different 
predetermined maps. The idle and full throttkle  voltages are just markers. The ECU needs 
to see voltage in a preprogrammed range  to determine "OK, that is the idle 
position." and OK, that is the full throttle  position"

<<The spritzer provides more gas as the butterfly is  opened, as qualified  
by the logic , other sensors on the bike, and ROM  data in the ECU.  
Since many bikes need enrichment to avoid surging and  otherwise be more  
tractable, some folks give the TPS an extra twist  (which results in  
higher voltage at idle... like the magic .385  volts). This gives the  
ECU the impression that the butterfly is more  open than before the  
extra twist was made and enrichens at every angle  of the butterfly and  
speed of the  bike.>>

Connect a voltmeter to the O2 sensor,  and you will quickly see that the TPS 
setting does NOT make the bike run "a  little richer". It does NOT "enrichen 
at every angle of the butterfly." If ift  did, we (BMW mechanics) would all 
have adjusted the TPSs ten years ago, and no  customer would have ever heard of 

<<The ECU can't  believe you really mean to be idling unless the voltage  
drops below .4  volts; so keep it below.>>

Actually, it can't  find its' start point, so it reverts to the "base map" 
which is quite rich and  can actually destroy your O2 sensor. 

<<The right voltage is  the one that makes the bike run nice and doesn't  
waste  gas.>>
The right voltage is .340-.385V. Anywhere in  that range is the same as far 
as the ECU is concerned.  

When you want to school the TPS, just disconnect the  fuse for the Fuel 
Injection Control Unit (on the R1100S it is the frontmost fuse  in the left-side 
fuse holder. You need five joints in your fingers to access  it.) Or disconnect 
the battery for at least 30 seconds.  

Next, turn the ignition key and kill switch to the  run positions, do NOT 
start the engine. Roll the throttle slowly to full  throttle, back to idle, hold, 
roll full throttle , hold, back to idle, repeat.  Three full throttle sweeps 
of the TPS, with a momentary hold at each end. Then  start and ride the 
motorcycle. Give it about ten miles to finish resetting  itself, it is not an 
instant process. 

Tom Cutter
Yardley,  PA