Re: O2 sensors AD #784

["C.M. Smith" <cmsmith@domain.elided>]

Definitely your Alfa engine management computer needs an O2 sensor to run
correctly. Without one, the unit will think the O2 sensor  has failed and
use the "limp home" circuit. Expect less power and higher fuel consumption
as the injection computer has to enrich the mixture to be on the safe side
until the O2 sensor is repaired (which it never will be if you leave it
off). Winter running may be especially rough and costly in fuel.

A common fallacy exists that emission controlled engines produce less power
than ideally tuned engines, therefore removing say the O2 sensor will free
the engine to produce more power. Not true, modern engines using O2 sensor
feedback loops have very high specific output compared to pre emission
controlled engines .

 Actually, pre O2 sensor engines could not reliably produce fuel mixtures
with the theoretical ideal stochiometric ratio of air to fuel, i.e. the
ratio at which exactly enough oxygen is in the combustion chamber to
completely burn all the fuel, producing maximum power available from a
given quantity of fuel. The O2 sensor is a vital part of the feedback loop
to achieve this. The O2 sensor changes its resistance (or develops a minute
current, I can't remember which) as it detects or fails to detect surplus
oxygen in the exhaust (it is temperature sensitive so must be placed in the
correct position near the exhaust manifold to work correctly, modern ones
have a little heater on them to assist in getting up to temperature
quickly). The fuel pressure is then adjusted (on K-jetronic,  possibly also
on the later L jetronic and Motronic as there is a pressure valve at the
end of the fuel rails) or the injector dwell is adjusted (on L-jetronic and
Motronic) to lean out or enrich the fuel mixture very rapidly. You can see
how this is a feedback loop.

SAAB has a system that is so accurate it actually "senses" the ions in the
combustion chamber after firing of any cylinder, using the sparkplug gap as
the part of the sensor. This info is fed back to the "Trionic" engine
management system which combines with the O2 sensor info to produce a 225
hp turbocharged ULEV engine that produces exhaust that is cleaner than the
inducted ambient air in most major cities in the world!!!

While there's nothing like the induction roar through a set of perfectly
set up and balanced Weber carbs ( or Dell Orto or whatever your favourite
happens to be) the fact of the matter is modern engine management computers
can't be beat. That's why all the F1 teams use them, and yes Virginia
that's an O2 sensor on that Ferrari V10 F1 engine.
Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner 

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