Re: MFA questions

[drew <drew@dyermaker.cs.uoguelph.ca>]

On Mon, 7 May 2001, Langford, Cory wrote:

>  While we seem to be on the topic of Multi Function Adapters, a few
> questions to anyone who has any info:
> 
> 1.  What sensors are actually needed to make a MFA work?  I figure I already
> have the oil temp sender in my '82, the trip meter is that done via another
> sensor, or one in the Speedo's odometer?  I know the outside air temp is on
> the bumper in my '86 with MFA, the L/100KM is done my what sensors?,etc...

The MFA uses input from the oil temperature sender, a hall-effect pickup
in the speedometer head (same sender is used with factory cruise control),
and an ambient temperature sender which is located in the left wheel well
behind the fender liner.  In addition, there is a vacuum sensor built into
the control unit which, together with a pickup from the tach circuit for
engine RPM is used to calculate average fuel consumption.

> 2. Can ANY one let me know how the L/100 km (mile/gal for you us folks)
> actually works?  On my '86 this is the only function that does not work.
> All other functions work fine, but this one always shows 0000, or ---- when
> clear the system.  I would like to get it working (even if I don't use it -
> I hate things that don't work in the car).  Anyone have a clue?

As I said above, a vacuum reading from the intake manifold coupled with
the wheel speed (from the speedo), engine rpm and possibly some sort of
map of predetermined values for the engine's power etc. result in the
calculation of average trip economy (supposedly instantaneous values are
available for this as well, but my 84's MFA doesn't seem to respond to the
procedure for bringing up the hidden MFA functions.)

If your elapsed trip function of the MFA still works, then it is possible
that the vacuum hose to the intake manifold is broken, plugged or
disconnected (although I always thought this would result in BAD mileage
figures as the MFA would be reading the engine's being at MAX power (ie
throttle plate always open=near zero manifold vacuum.  But 0000 L/100km
is REALLY GOOD mileage - damn good, in fact... :))

If your trip function doesn't work, then it's likely a bad or missing hall
effect sender in the speedometer, or that the printed circuit connector is
loose, dirty or corroded, which was the case on my 84.

If it's neither of these, then the MFA is likely bad, or for some reason
it's not getting an engine rpm signal.

Hope this helps,

Drew (84 Wolfsburg with overly-optimistic mileage on the MFA courtesy of
tall gears)

> Thanks
> 
> Cory
> 

Drew MacPherson, Network Analyst, University of Guelph

drew@dyermaker.cs.uoguelph.ca           |  visit the Massey-Harris page:
http://dyermaker.cs.uoguelph.ca/~drew   |  http://m-h.cs.uoguelph.ca


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