[200q20v] Department of Obscure Information
pjrose at frontiernet.net
Wed Jan 30 18:31:10 EST 2002
You're cruising along. The car is running very nicely. At such times,
one's mind can turn to mush (or at least to trivial thoughts)...
My late-build sedan (Lago) does a "miles 'till empty" (MTE)
computation that is clearly based only on the most recent interval of
driving (i.e. a very short-term MPG average). So, it updates the MTE
usually at 5- or 10-second intervals (when driving at 60 MPH or
faster) to reflect the latest bit of driving. It quite clearly does
not calculate MTE using the (longterm) average MPG shown on the
computer. In other words the MTE is based on fuel consumption right
_now_, rather than a rate of use influenced by conditions hundreds of
miles ago. I like that approach. It appears to function pretty much
as is described in our owner's manual.
On the other hand, I've concluded that the computer in our
earlier-build sedan (red) calculates its MTE value differently--on
the basis only of the long-term average MPG. It does _not_ use a
value from recent fuel consumption (i.e, MPG that's based on a recent
interval of driving.) Who cares? Well in that case the MTE can be
way off--being considerably under- or overestimated in situations
where a change in driving conditions cause the rate of fuel
consumption to change considerably (a 50% change is not uncommon).
This "miscalculation" will persist for quite a while if you had
established the previous MPG average over a large number of miles.
This is not a good method for estimating MTE, IMO. Oh, in addition,
it seems that the red car updates its MTE value much less frequently
than the Lago car's computer--using intervals of at least 20 to
30-seconds rather than every 5-10 seconds.
One other comparative item (related to Chris Miller's stress-crack
"survey"?) My red sedan has the line of cracked paint, showing stress
across the gusset between the passenger strut tower and firewall. But
as previously reported to Chris, our much higher-mileage (and
harder-driven) Lago car has no evidence of stress at that point.
Phil Rose Rochester, NY
'91 200q (130 Kmiles, Lago blue)
'91 200q (57 Kmiles, Tornado red)
mailto:pjrose at frontiernet.net
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