[mdlug-discuss] OBD fuel monitor fine tuning

[Robert Meier]

Aaron, Drew,

>>> If I remember correctly, a perfect stoichiometric mix is
>>> actually TOO LEAN -- it will burn out your engine.  The
>>> reason is that unburned fuel inside the cylinder absorbs
>>> some of the heat, and thus COOLS the engine.

My understanding is that this is true of current air-cooled aviation
piston engines, but that it is obsolete for ground car engines.

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.

If I understand correctly, 
todays ground car engines do indeed run much hotter,
nearly stoichiometric, but slightly lean,
and are designed to tolerate much higher internal temperatures
than their rich-running predecessors of twenty years ago.

>> ... especially with a cold engine, ...

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.

Reporting,
-- 
Robert Meier

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