[Gmecm] Re: Fuel economy

Thu Sep 15 06:41:15 UTC 2005

Bah!
Have you ever even observed the nb O2 sensor when hwy mode is active??
(I certainly have and it's typically buried somewhere BELOW 150mV)
The O2 sensor is doing NOTHING as far as feedback for HWY mode is concerned 
(as if it even COULD)
The AFs you are quoting are projected AFs based on fixed "staged" drops in 
injector BPW at the listed LV8 variables (again assuming all of the enable 
criteria for HWY mode had existed)
Once nb voltages depart from 450mV it becomes essentially USELESS with 
respect to measuring AFs. All that can be said is O2 voltages ABOVE 450mV 
are RICHER than stoich and those less than 450mV are LEANER than stoich- 
that is all. By HOW MUCH richer or leaner cannot be established using ANY nb 
technologies that I am aware of.

JMO
WopOnTour
----- Original Message ----- 
From: "Mark Romans" <romans at starstream.net>
To: <gmecm at diy-efi.org>
Sent: Wednesday, September 14, 2005 7:25 PM
Subject: Re: [Gmecm] Re: Fuel economy

> >From the bins I have looked at, 89 1227165 corvette (YB) and Camaro
> Firebird(FB) code
> the hwy fuel code is there.  There is also hwy spark, the hwy spark is 
> enabled however the hwy fuel is not.
> In the code there is
> CTS disable hwy fuel is LV8 is > this
> Degs disable hwy fuel if coolan =< this
> SEC lock out hwy fuel for this long
> SEC max time in hwy fuel
> MPH Disable hwy mode if veh speed is =< this
>
> Stock settings are 140 for lv8
> coolant temp 167 or below
> 10 seconds before hwy fuel is entered
> 60 sex max time in hwy fuel
> 55 mph min mph
>
> AFR settings
> 32 LV8 counts = 15.3
> 64 LV8 counts = 15.3
> 96 LV8 counts = 15.0
> 128 LV8 counts = 14.7
>
> I can also tell you that you can change the switch point on the 02 sensor 
> to a higher or lower afr.
> Mark
>
> ----- Original Message ----- 
> From: "Cowen" <captain_krill at yahoo.com>
> To: <gmecm at diy-efi.org>
> Sent: Wednesday, September 14, 2005 4:25 PM
> Subject: [Gmecm] Re: Fuel economy
>
>
>> 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.
>>
>>
>>
>> **********************END TRANSMISSION**********************
>>
>>
>>
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