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Re: Tach Fails When Warm

Kevin,

I am not a mechanic, and I don't have a BMW (but I play one on TV ;^>). 
But...  if your tach is electronic (only very old cars have mechanical
tachs) then you have an electronic circuit driving a meter.  The
electronics has to get it's signal from something, usually something in
the ignition.  

If the tach fails when the engine gets hot, look at the pieces that get
hot with the engine, like the sensor.  Don't bother with the tach
circuitry in the dash until you know you are getting a signal to it -
that can be as simple as hooking a Radio Shack voltmeter (use the AC
position, it won't be accurate cause your looking at a square wave or a
spike, not a sine wave like the voltmeter is calibrated for, but it will
tell you if you've got signal) across the wires going into the tach
itself.


- -- 

Jacob J. Steijn                2633 Abington Rd.
[email protected]           Wilmington Delaware 19810
302.475.5908                   U.S.A.