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2475Re: speedo/OBC problem [bmw e28] Digest Number 567?

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  • sheetfar
    Jun 15, 2004

      I have since fixed the problem, as mentioned in a previous post.
      (Also, I might add that the cruise control didn't work, either.)

      Thanks for the input. I had forgotten that they use the same
      electronic sensing devices in cars that are used in robotics and
      conveyor systems to locate the position of an object. Your mention
      of the Hall-Effect brought that back to mind. Perhaps the
      word "transducer" doesn't apply here. Maybe "proximity switch" does.
      Thank you for the correction and help.

      It is nice to know that people who have worked with various
      electronic devices and industries use this newsgroup.


      --- In bmwe28@..., "Stuart Logan" <stuartlogan@e...>
      > The Speedo is electronic in these cars, so any work to the rear
      > axle, - specifically the 'transducer' as you call it, would be
      > the direct cause of these issues.
      > Also, the Fuel economy gauge is NOT a Vacuum gauge of any sort.
      > It is a relatively direct display from the Engine FI Computer
      > showing fuel delivery rate .vs. speed (from) the 'tempo' signal
      > generated by the hall effect unit in the rear axle (the same
      > unit that supplies the Speedo, OBC, and Cruise Control).
      > Stuart Logan
      > '83 528e
      > '84 528e
      > '85 535i
      > '82 733i
      > -----Original Message-----
      > Message: 1
      > Date: Mon, 14 Jun 2004 19:42:44 -0000
      > From: "sheetfar" <sheetfar@w...>
      > Subject: obc/speedo don't work
      > I have a 1986 528e with a manual transmission.
      > Recently, the following things have started to malfunction:
      > * Speedometer doesn't work.
      > * White-needle vacuum gage (located just below tach) doesn't work.
      > * On Board Computer OBC works except for the fuel consumption &
      > driving speed (MPG & MPH buttons).
      > After driving the car for 20 minutes or so, the vacuum gage starts
      > cycling on/off every 2 seconds. Eventually, the speedometer might
      > work after the vac gage starts working properly.
      > I replaced the expansion valve on the A/C evaporator last month.
      > However, everything (all instruments were checked) worked fine
      > after that.
      > The most recent work was done several days ago on the rear axle
      > portion of the car. If the differential transducer has a bad
      > connection or has malfunctioned, could it cause any of the
      > speedo/vac gage/OBC problems?
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