[Gmecm] Re: Fuel economy

Thu Sep 15 19:12:45 UTC 2005

Sorry Mark
(That came across poorly) I wasn't insinuating you were riding in your first 
rodeo :)
It WOULD be interesting though to see how close the actual AFs (as measured 
by a WB) compare to the assigned AF variables assigned (LV8 triggered) in 
the calibration. I've often wondered if the fixed base pulse width reduction 
used was offset somehow by "weighted" BLM cells or something. I mean if the 
system has already "trimmed out" a dragging fuel pump by increasing most 
LTFT/BLM cells to say 137 to compensate... is this "factored in" somehow so 
that when HWY mode engages, it's not TOO LEAN. I've never seen existing fuel 
trim values ever listed as an enabling criteria for hwy modes.
Regards
WOT
----- Original Message ----- 
From: "Mark Romans" <romans at starstream.net>
To: <gmecm at diy-efi.org>
Sent: Thursday, September 15, 2005 8:01 AM
Subject: Re: [Gmecm] Re: Fuel economy


> This isn't my first rodeo!
> I'm not saying it's accurate!   I'm just telling you what the code says!
> Yeah, the 02 sensor goes down to nothing!  I do have a WB but I haven't 
> had time to try
> it with the Hwy mode enabled.  I can tell you that before I had the wb I 
> used to try to go leaner
> and the fuel economy goes down when it gets so lean that it lean misfires!
> And I agree it's totally a guestimate as to what the actual afr is.
> As far as melting pistons, it's not gonna happen, this is at exremely 
> light loads.
>
> Another interesting point is that years ago Bruce Plecan and I were 
> discussing this and he made
> the comment (And you know he TESTS everything) that he was actually seeing 
> increased fuel economy
> and drivability with slightly richer than stoich afr's.
>
> Mark
>
> ----- Original Message ----- 
> From: "WopOnTour" <wopontour at hotmail.com>
> To: <gmecm at diy-efi.org>
> Sent: Wednesday, September 14, 2005 11:41 PM
> Subject: Re: [Gmecm] Re: Fuel economy
>
>
>> 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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