O2 Sensor Bias

[greg kring]

Excuse me, kind of new here. What's wrong with lowering fuel pressure to lean
out the mixture "across the board" as you want. Since GM ECMs go into open
loop at wide open throttle (signaled by the throttle position sensor) the best
way to lean it out, or richen it for that matter, is by changing the base fuel
pressure. Lower the pressure until you get the O2 readings in the range you
want (800-850?). Unless your base fuel maps are way off or the injectors are
sized wrong that should work, right?
greg kring


Walter Petermann wrote:

> Woosh...
> never heard of that, but then I'm not familiar with GM. Ok, so
> you're saying that if the ecm is tracking at a certain location
> in this '18th block', which can be tweeked by biasing the O2,
> then the ecm will remember this setting and use it as a 'base line'
> to calculate fuel at WOT?
> Have you come up with a circuit to add the voltage to the 02? I can
> give you a hand with it Sunday morning.
>
>   Walter
>
> PS If the car senses full throttle with a switch you could try
>    disconnecting it.. just a thought.
>
>
> Kurek, Larry wrote:
> >
>
> >         >  Excuse the jumping in the middle of the thread again...
> >         >  If the reading is 900mv at WOT then the ecm is either not
> >         >  looking at the O2 or is already maxed out lean and can't lean
> >         >  any more. Adding 50 or 100mv to the O2 reading won't help.
> >
> >         No problemo!
> >
> >         Actually, the way the PCM in the LT1 works (and most GM's for
> > that matter), is that it goes open loop at WOT (actually, I think it is
> > 40-50% throttle opening, but I could be wrong on the exact number).
> > However, what it uses for fuel trim is the 18th block in the BLM, which
> > is established as the max block prior to WOT operation. If I can force
> > the ECM to trim the fuel leaner accross the board, then at WOT the fuel
> > should be trimmed as well.
> >
> >         TTYL!
> >
> >         Larry