moving o2's for headers, how does voltage change?
 

i was just wondering if a cooler sensor will read lower or higher, im just trying to come up with idea for adjusting their opperation that could maybe eliminate the need for hotter o2, or at least play around with the idea.

i know at WOT my numbers read about 30 mV higher than they used to when the car was tuned right.

A cooler sensor will return a lower voltage, so the pcm will think the car is running lean and will add fuel, making it run rich. Normally you'll see this at idle because of the lower exhaust volume/flow. At wot the sensor should be hot enough.

There is a table with voltages (I forget the exact name, something like midpoint or switching voltages) that represent a cooler sensor at idle.

There have been a couple of posts about lowering those voltage settings in that table, to an even lower setting for cars with headers. I used that approach on mine and it helped with a rich idle.

The O2 sensor voltage in the rich region goes up w/
lower temperature - to a point. But the sensors are
supposed to stay above a certain temp or they
just don't work at all, and then you get nothing
(low voltage). That's the problem - long tubes can
be so cool that you don't get a useful voltage out,
it looks lean even if it's rich, and your closed loop
is not closed anymore (in the sense of negative
feedback) but the PCM has no clue until it throws
the heater code.

Lowering the threshold can help some if the O2s are
switching at least a little. But when you see the O2
switching waveform become asymmetric (not a 50/50
square wave of varying frequency) they're not happy.

i think your talking about the o2 error tables john and this is what i was referring to, if this is whta you are talking about. now i wonder this, my o2s oscillated nicely before my injector install and now im going back and forth on trying to fix it, ill post up a pm i sent out to mnr-o abuot this.

but i am just wondering if my idle switch point is too low and my car is trying to pull too much fuel, maybe i should up my idle switch point to about 400-425 or so to get closer to the 14.7 mark. the car is actualyl showing rich on me at idle after the swap, let me copy the message and post it back up

i need your help brainstorming here, im off today and im gonna try some things out.

ok well as u know i was having idle issues with my injectors. i put the injector size in smaller to make the car run rich, when i did this, the car ran just like it used to and the idle oscillated nicely, but was reading pretty rich. i tuned the VE to compensate for the richness and that stopped the nice o2 oscillation i used to have and started to give me troubles again idling. right now the car runs good except for idle conditions, anything under the thresholds for idle give me trouble if i pull out fuel. i was thinking it was a few things

1)maybe it gets my pulse width too low and causes injector misfire.

2) maybe my proportional numbers are too low or high to not give good oscillation

but then i started to think, if i force the car to give better oscillation, it will put in too much fuel, and i will run rich. i want to fix this and not run rich. the only thing i can really think of is, ok the car does want to run ok at low fueling but the injecotrs dont want to inject fuel at that low of a pulse width so maybe i need to up the minimum values to 1.5ms where racetronix said is the limit. but then i go bac and say, well how come this takes away my nice oscillation??

if i up the proportional tables will that help oscillation and not hurt the fueling at idle and make me rich? i feel like im stuck in a pickle here and if i go one way to correct and get further from one problem im getting closer to another problem. there has to be some adjustment in there to correct for this?? maybe my o2 error tables are set too high at the higher mV readings? that was a thought that just came up, what do you think??

I think my table had somewhere around 360 mv and I dropped it to 320. If you raised yours, that may be part of the problem.

You're right, when you start chasing the problem around in several tables, it turns into one big circle...

What size are the injectors?

38#

mnr-o said sometimes you run into problems idling with high impedence injectors, but racetronix and others say these should do fine

Yeah, 38's should be reasonable. I just fired mine up this morning and drove it for the first time with a new set of 60's in it...

Did you make any more headway with it?

well i think i might go out on a ride tonight, maybe, and see how it looks. the idle quality is pretty good i think and the car responds nicely, i just have to go and see how the fuel trims are acting now so i can make any further adjustments

i just went out and tried some things in the drive way. i tried adjusting the o2 gain down and it seems that was causing some hunting problems again for idle when the o2s were maxed or mininum, im going to try to increase this number and see if it will do the reverse and help out.