[mdlug-discuss] OBD fuel monitor fine tuning

[Aaron Kulkis]

Drew wrote:

<snip happens>

> 
> < math snipped >.
> 
>      But this still doesn't tell me, given values for fuel trim, how to
> calculate the actual deviation from stoichiometric mix that the
> engine is running at the time. Especially as there are *two sets*
> of short term and long term Fuel Trim values. Do I add them all
> together, or average them, or some other combination?

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.

This solved the riddle of why old manuals (back in the
carburetor days) always warned that leaning out the
fuel mixture too much would cause engine overheating,
and eventually engine damage.

And this is why we have catalytic converters...because
an automobile engine functioning as designed WILL have
unburned fuel in the exhaust.