[mdlug-discuss] OBD fuel monitor fine tuning

[Drew]

On 10/22/07, Robert Meier <eaglecoach at wwnet.com> wrote:

> If I understand correctly,
> the current system (possibly EPA-mandated?) adjusts the fuel mixture,
> so that the pre and post catalytic oxygen sensors report a slight
> (nearly zero, but within measurable bounds) excess of oxygen.
> This results in (ideally) no unburned gasoline output from the engine,
> and tolerable NOX byproducts.

    That is how I would design it. For that matter, I would make the possible
adjustment range as wide as possible, capable even of leaning out the mix
to zero fuel, just in case the owner obtains an alternate combustible (eg,
woodgas, methane, hydrogen) and wishes to feed that into the intake along
with the air, to suppliment or replace the usual fuel.

    With the rich-lean mix self adjusting in this manner, it should
matter a great
deal less what is used as fuel, the only other issue that I know of that needs
to be dealt with being spark advance.

    But then again, I'm used to thinking about such things for my own personal
use, rather than for sale to customers who either don't care or are not to be
permitted possession of omnivorous engines.

> It has been my understanding also that a cold engine should be run rich,
> but I cannot confirm this by my observations of my Saturn SL2.

    Are you getting negative fuel trim readings when first starting your engine?
Perhaps the OBD documentation on fuel trim does have the signs reversed.



>   "Baseball is 90 percent mental; the other half is physical."
> 	    -- Yogi Berra

    He's smarrrrrrrrrter than the average baseball player.

----

 - Drew.