02 sensor readings from manifold to headers

[ZL1Killa]

buddy of mine has a 00 trans am ws6 with pacesetter headers and according to what he is thinking he should re-program his 02 sensors to either a higher or lower value for stoich reading.

So here is the story behind this: Stock exhaust manifold and stock placement of 02's. you then have pacesetter headers and y-pipe; the 02 sensor is lower and farther away from the stock position so the 02 sensor should be re-programmed to properly read stoich back to the car because it is going to see lower temperatures.

this all being said; I thought that the 02 sensors were self heated, they just took a while to warm up, and the reading, once warmed up wouldn't matter where it was...as long as it wasn't FAR away from the header due to innacuracy , such as readings from a wideband in the tailpipe.

is any of this right? because i don't think that you would need to recalibrate the 02s as long as they were in the header somewhere????

[SSpdDmon]

Some people switch to the rear O2's off of a C5 to compensate. LS1tech.com has had this discussion in the PCM forum as well. Personally, I would think changing the O2 swith points by .030~.050mV to accomodate for moving them back could work. But, I wouldn't do it without confirming with a stand alone sensor that works (ie - my LC1). Looking at the graph of a stock O2 voltage output real quick, I would presume you need to reduce the stock switch points. Again...I wouldn't do it by more than .050 mV though.

[ZL1Killa]

ok..my friend has pacesetter headers and he is using those new 02's as you said in your post.

I will talk to him tomorrow and see all what is going on and how he has adjusted them

[PSWired]

Umm, correct me if my thinking is wrong here, but is the O2 sensor switchpoint temperature dependant? The position of the sensor in the stream will only alter the amount of time present between a rich-to lean commanded switch and a measured switch, and the overall temp of the sensor. I would think the switchpoint voltage would stay the same regardless of these two changes...

[dfe1]

Umm, correct me if my thinking is wrong here, but is the O2 sensor switchpoint temperature dependant? The position of the sensor in the stream will only alter the amount of time present between a rich-to lean commanded switch and a measured switch, and the overall temp of the sensor. I would think the switchpoint voltage would stay the same regardless of these two changes...

You're actually thinking correctly-- the O2 sensor is fed a reference voltage of approximately 450 millivolts which equates to stoichiometry. Narrow band O2 sensors are essentially switching devices. Even though output voltage will vary between 0 and 1000 millivolts, the only thing the PCM cares about is whether output voltage is above or below reference voltage (which indicates either "rich" or "lean"). Once the exhaust leaves the combustion chamber, oxygen content doesn't change. The position of the oxygen sensor within the exhaust stream is much more important than its distance from the exhaust port. If the sensor doesn't read a homogeneous mixture, readings will be skewed. In most cases, chasing the change in voltage isn't worth the effort. The question is, since sensor voltages continually switches, how are you going to determine whatchange to make?

[mistermike]

I have experimented with dropping the switching voltage as low as 300 mV in an effort to correct a slightly rich condition under closed loop. It basically hasn't had the desired effect. My AFR oscillates around 14.4 instead of 14.7 on both banks. I'm not sure if I have any other options. My OS has no stoich adjustment.

[dfe1]

My AFR oscillates around 14.4 instead of 14.7 on both banks. I'm not sure if I have any other options.

That's because of the hydro-carbon rich air in Cleveland.