At 04:32 PM 6/14/00 -0700, you wrote:
>I understand this, but I thought the whole point of closed-loop mode was
>that the computer watches the O2 sensor, and cuts back the fuel to keep it
>running at the right A/F ratio. .Geoff
My understanding of how it works in general.
The O2 sensor is a narrow band type as opposed to the wide band type
(very expensive both initially and to maintain). Narrow band type
has less resolution capability i.e. cannot do fine readings.
When our O2 sensor send voltage output to the computer, the computer
only knows what that reading is for stoich (14.7:1 AFM ...cats run
most efficiently at this ratio) and possibly a tiny bit up or down
from it. When O2 sends a voltage, our PCM basically only knows
it's a rich or lean condition but cannot tell by how much. It does
into a 'crude' calculation based on this input plus inputs from
other sensors and comes up with a pulse width figure. If O2 input is
seen as rich condition, it calcs a shorter pulse width and very
quick reads O2 again. If O2 is still rich, it'll take the sent
pulse width and use it as a base for another calc. and come up with
a shorter pulse width. Reverse happens if O2 input is a lean condition.
It keeps doing this ... if you've seen a scanner or have a AFR gauge,
you'll see gauge or light indicators bounce continuously between
rich and lean, sometimes showing rich (or lean) a little longer.
At any rate, our computer is calibrated for 19# injectors. When
bigger ones are put in, computer does know ... just continues
making pulse width calcs based on 19# flow. So, if sensor inputs
(not fine resolutions) are similar, pulse width calc. will be similar
and with 24# injectors, more gas will flow into the engine than with
19#.
Sorry for the length. I'd like to hear from anyone with a different take
on this.
Bob
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