O2 sensor bias

[Walter Petermann]

John,
I suspect that the egr is increased when the computer spends more time
leaning than it does richening. In other words, it's not increasing
egr in response to a shorter pulse, but to increased duration of
the richening cycle versus the leaning cycle. 
These are the reasons (those with knowledge of GM ecm insides correct me)

To know that the injector duration is smaller than it should be the
ecm would need to be constantly comparing actual pulse duration with
a reference fuel map. As I understand it though, the inj duration is
already generated from the reference fuel map.

>From my experience with L-jet cars, 0-30 accelerations seem to be made
lean on purpose, probably for better city mileage numbers. If this
is the same for GM cars, the extra time the O2 spends lean during
acceleration is probably used as a trigger for increased egr. I can
see this being extended to all driving conditions: any time the 02
spends more time lean than rich, the egr is activated until the
lean and rich times are equal. If the added 02 circuit unbalances
these times, for all conditions and at all times, then the ecm would
just keep increasing the egr until it's maxed out.

It would be nice to be able to take a look at this 02 circuit add-on
and get an idea of exactly what it's doing, but I couldn't find it
on the web site you mentioned. Seems like what is needed (at least
to see if it fixes the egr problem) is a circuit that changes the
o2 voltage but somehow makes the ecm cycle evenly.

As someone used to be fond of saying, maybe the above is just a
brain f@#t! Any comments?

 Walter 


John Wickerham wrote:
..
> 
> Well, I was expecting that by adding 100 to 200 millivolts to the O2
> voltage that I might be able to get a bit better mileage.  My intention
> at the time was to also run water injection to prevent too much heat,
> etc...
> 
> While testing it alone, however, I noticed that mileage did not change
> at all over quite a bit of testing.  I cranked up the voltage to about
> 400 milivolts since the device did not seem to be effecting the way
> the engine ran in any way.  Within a few minutes of driving, I got an
> EGR fault code.  Checking out my Haynes manual revealed that the
> computer had commanded more than a 50% duty cycle on the EGR valve,
> and that wasn't allowed.
> 
> Upon lowering the voltage, the fault code went away.  I assume then that
> with increasing O2 voltages (or resulting narrowed pulse widths on the
> injectors) that the computer also calls for more EGR since the mix is
> now leaner.
> 
> Just my guess as to what is happening, but I think the additional EGR
> is preventing me from getting an advantage from the leaner mix.
> By the way, you can get one of these devices from www.eagle-research.com.
> Price is I thin is $49.95.