General EGO info (Bosch)

[Jason_Leone at amat.com]

cwagner at info2000.net wrote:

<<<so I disconnected the EGO sensor to
mess around with it to see why the rich mixture.  During idle, the
reading on a DVM is almost zero.  Any other time it is around 600
mv.   From what I have read, this indicates a rich mixture but the
computer doesn't set a code for a rich mixture.>>>


Well, I'll just take this chance to copy/paste a post I did on another list
quite some time ago...about Bosch EGO parameters. It probably doesn't help the
above list member, but it's archive type info...just the same. Enjoy.

<snip>
Here's a little Bosch Lambda chart:

       Voltage curve of the Lambda sensor at
        an operating temperature of 600*C.

              0.6   0.8   1.0   1.2   1.4
              =============v=============
         1000 | -------\   .
     V        |         \  .
     o        |          \ .
     l    800 |          | .
     t        |          | .
     a        |           \.
     g    600 |           |.
     e        |           |.
              |           |.
          400 |           |.
   (mv)       |           |.
              |            \
          200 |            .|
              |            .|
              |            .|
            0 |            . \-----------
              ===========================
              0.6   0.8   1.0   1.2   1.4
                    Excess-air factor

The value of "1.0" is the stoichiometric air/fuel mixture. Most Bosch
EGO sensors have a range of .75 - 1.2
Temp has a lot to do w/ switching times on the Bosch EGO. For example,
at 350*C the switching times are about .1 second, but at 800*C they're
about.05 second. That's a 2:1 change in switching times due to changing
temps!

Also, the switching characteristics of the EGO needs to be considered
too. If you slowly vary the A/F ratio from lean to rich and graph the
switching points...then slowly vary the A/F ratio from rich to lean and
graph the switching points on the same graph...you'll find that the
spline curves do not overlap and are not identical. This phenomenon is
known as "hysteresis". You might not really need to know these things, but if
you're relying on the EGO to save your pistons from meltdown...it can't hurt.
Knowing the characteristics will help troubleshooting and diagnosis...as well as
tuning.
<snip>

Jason
'93 SLC