Re: E30 cruise control brain location

[Jim Cash <j.cash@xxxxxxxxxxxx>]

Alexander Fadeev writes:

> My cruise control is starting to act up. Everything points towards
> an intermittent electrical connection (going over bumps resets the cruise,
> after a few additional bumps it will come back, etc). That plus the fact
> that cruise control is pretty difficult to trouble shoot (since it works
> only at speeds above 28mph (45kmh)) prompts me to clean up all the
> components before I start swapping things out. 
> Does anybody know where under the dash in '89 325i cruise control
> box is physically located?

Alexander

I am not familar with the E30 so can not answer your question about the
exact location of the cruise box.

But even when you find it te best you can do is stare at an electronic
component box - you might check that the connector is tight, and of
course it is "possible' that there is a bad solder connection inside -
but frankly I would start looking other places first.


Going over bumps resets the cruise - and then it comes back.

Here is what to look for:

 - All you power connections (especially fuses) are tight.

 - Does your speedometer also drop at times when you hit bumps - if so
the fault is not the cruise but the speedo circuit - probably te sensor
connection at the rear differential.

 - Or there is another connection at the back of the speedo (single
connectoron rear of the instrument cluster) that sends the speed signal
to the cruise - if this is loose you get same fault.

 - by any chance is your brake (or clutch) pedal bouncing a bit on those
bumps - just enough to operate the control switchs attached to each. The
crusie must get a ground connection "through" the brake light bulbs for
it to operate. If the clutch, or brake light switches operate, even
briefly the cruise cuts out. Need to readjust the switch position.  Even
a loose brake light bulb, or connection to ground can do the same.

 - And finally inside the cruise actuator (the control unit under the
hood) there is a rheostat tat provides feedback to the unit under the
dash. If there is any dirt on the moving rheostat connection, you
guessed it - the cruise cuts out.  If you open this unit be careful -
springs have been known to pop out  -and make not of the way the cable
is wound on the wheel before taking it apart ( unless you like puzzles
).

 - And finally - could it be the control lever is getting sloppy, and
activating with a downward deflection on those bumps?


- - Oh Yea - I forgot. Make sure you have full voltage at the fuses.  I
had corrosion in the battery cable to the fuse box, and this was just
enough to effect the cruise - it would drop out briefly at times - bumps
or no bumps. 


There - just when you thought your main issue was finding that underdash
unit.


Cheers

Jim Cash
London, Ontario,Canada
BMW CCA 102929

PS  - What do you mean you can't trouble shoot it in the driveway?  You
just have to fool the car into thinking it is going fast enough.  Just
make a pulse generator and attach it to that differential sensor lead  -
to mimic the pulses from the sensor.
No I do not know of one, your comment got me wondering about this -
there must be a way.

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