[Gmecm] Re: Fuel economy

[Cowen]

Darrell, 
Take a look at what the guys on the Wide Band O2
sensor sites are saying about fuel economy.  Our
Narrow band OEM O2 sensors are most sensitive at a
fuel ratio slightly richer than optmial for economy. 
One theory is, if you can get your O2 sensor to work
at leaner ratios, maybe you can tune for better
economy.

The other option people have mentioned is that some GM
ECMs (which bins??) have a disabled "Highway Mode" in
their program.  From what I understand, Highway Mode
is designed to ignore that narrow band OEM O2 sensor, 
only when a bunch of factors convince the ECM you're
under light load and at highway speeds.  Again, this
allows for tuning a leaner mixture than the OEM O2
sensor could use.  Unfortunately, the ECM is blind in
this mode.  It's not referencing the O2 sensor, so it
can't monitor emissions or mixture.  As a result, US
federal gov't has dissallowed use of Higthway Mode
from the factory.  It can also be pretty destructive
if enabled, because with no reference to the O2
sensor, there's every possibility of running WAY off
on the mixture.  Too lean and you melt pistons!  The
ECM wouldn't know to correct mixture problems because
it's not even looking when in Highway Mode. If you
have an '87 2.8l with 300,000 miles on it and one
injector is badly plugged, while another one or two
are partially plugged, they won't allow as much fuel
through as they would have on a new car (for which the
Highway Mode was written), and you'll run lean.  You
can probably imagine other scenarios where a high
mileage car with 20 year old components may vary from
factory norms!

Those are the only two ideas for increasing mileage I
can think of that are directly related to the
injection.  Of course better intake and exhaust help,
so that you're putting less energy into
pulling/pushing gasses around.  You can also make sure
your tires are pumped up at least to the maximum on
the sidewall.  If replacing your tires, consider going
as narrow as possible in as smooth a tread as you dare
for reduced angular inertia and rolling resistance. 
Keep your car light (leave the jack and spare at home,
and buy a smaller battery, etc.) to reduce mass you
have to accelerate.  The electric cars are great
inspiration for this!  I've heard the carpet from a
Viper is hollow to reduce mass - maybe you should put
some of that in the Cavalier! :)

There are also plenty of (snake oil?) products that
purport to imrove economy, but according to US Gov't
EPA tests, they either hurt emissions or cost more
than the fuel they save or both!  While researching an
article on what to do to pass emissions tests, I did
come across a few products that did reduce consumption
without increasing emissions.  According to the EPA
tests
(http://www.smartcarfinder.com/articles/gas/04.htm),
those product are things like an airdam/spoiler kit,
underdrive pulleys for your accessories, and driver
behaviour modifiers like idle alarms and bricks under
the gas pedal!  Does anyone else have any ideas??

I fear that most of these ideas will make so little
overall difference as to be moot.



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