In my searches on the forum, I've read that a cam with lots of overlap will let unburnt oxygen through into the exhaust and skew the o2 sensor reading lean. The fix for this is supposedly to slide the oxygen sensor bias voltage down a little compensate, but how far? Right now if I let my blazer idle in the driveway long enough, the headers start to glow a dull red. Obviously, it's too lean, even though my cross counts and BLMs are dead on. Using the glowing headers seems a little inexact, and I really don't have access to an EGT setup. Is there any other good way to calibrate the o2 bias, or is EGT pretty much it?

Teeleton

 

Its not the leanness that makes them glow, though logic would make you thinkthat.. What makes the glow is the unburned fuel that comes out with the unburned oxygen.
The unburned fuel end ups burning in the header causing the glow. I would first try raising timing some at idle to see if that helps the situation, but it probably will not.

A great tool in aiding this is a hand held pyrometer, maybe a friend has one, or you can buy a craftman one for like $50.oo
and they are well worth it.
At idle you are want the surface of the header to be between
180-400 They will vary a little - like because the center feed off one another and 5 and 7 fire one after another.
But for your header to glow they are 500+ degrees. Mine were in excess of 600 at times and lowering the bias did not help enough, I had to run the car open loop which really did not bother me.

Another way to do this is lock BLM to like 132 or so, that way you can lean out at idle but the ECM will only try and compensate soo much, while not over ruling your command.
What happens is the unburned oxygen make o2 think you are lean-therefor it adds fuel, or you do because your BLM is high, that is much un needed causing it to burn in header.

 

What makes you say, it's lean?.
It's EGT that makes them hot.
EGTs can be high, for reasons other then afterburning.

 

Retarded ign. timing causes the mixture to complete its burn after the exhaust valve opens which may be contributing to the glowing header/manifold.

 

Wouldn't sliding the O2 gain down, at a given mass flow rate, skew the tune even leaner? IE Reducing the gain on the sensor voltage will make the exhaust look even leaner to the computer. So increasing the O2 gain at low MAF readings should skew the readings "richer", right? I have read all of the posts I found searching about O2 gain. However, everyone talks about changing the O2 VOLTAGE gain, while the 6E code in Tunerpro deals with just a 0-1 proportional multiplier I have a choppy hydraulic cam in a 327 that causes my BLM's to max out at 160 unless I bump up the MAF tables around idle a lot (which then makes my calculated LV8's rediculously high at idle, around 50) When I richen the idle, via MAF table #1, enough to obtain around a 128 BLM at idle, the exhaust smells obviously way over-rich. With the exhaust smelling decent, my O2 readings end up being artificially lean at idle and the BLM's jump up and max out really quickly. I have my O2 sensor gain increased to 1.0 across the scale (thinking this will skew the readings rich -- someone please correct me if I have this backwards). I am going to end up tuning the idle by smell and locking the max blm to 135 or 140 (where I have it now) and ignore the O2 at idle. If I am indeed understanding the gain correctly (higher = richer reading to the computer, ie doesn't have to increase the BLM/INT) then there is not enough room for me to increase it to my satisfaction at low flow / high overlap conditions. If I could crank the gain up to like 1.25 at idle (can I hack this in the code? Tunerpro won't let me save a value higher than 1.0 for O2 sensor gain) then the unburned oxygen pumped through the exhaust by my cam would actually be compensated for and I could get the idle BLM to behave itself. OR can I lock the BLM cell #1 (1000 rpm and under for me currently) to 128 but have all higher cells active? I know there is a minimum LV8 you can set to update the BLM's, but I can't get it anywhere near high enough. I idle around 35 LV8 with the stock MAF tables, and around 40-45 with the modified tables to get the idle "rich enough" according to the O2.