Im always reading how stock o2 is only accurate at or near 14.7 ratio , but everybody on here seems to use WOT readings to tune their setups.
Is the readings close enough and sensitive enough to judge affects of part changes based on wot a/f? How different would wide band readings be compared to stock o2's? I figure some dyno operators on here might have tested this.

 

ANYONE? <img src="images/icons/rolleyes.gif" border="0">

 

Autotap/TechII/Scanmaster are not as ideal as using a AF gauge on a dyno, but they are still pretty effective.

Last time I used a TechII, at WOT my O2's were like 970... Way too rich.

I'll use one of the above and tune at the street/track for about 900 02's, and then dyno it when I can and look for a 13:1 AF.

Oh, and when I dynoed the ARE 422ci, I dynoed 433rwhp with a 13.5:1 AF and my 02's on the way down there hit like 770, so I was waaay too lean. I had to install a new intank pump for the big motor. Now I have too much fuel pressure, it's like 61lbs at idle.

[ January 16, 2002: Message edited by: Pro Stock John ]</p>

 

Think of O2 readings as ballpark figures.

Examples...

.700mv and you KNOW you're way too lean.

.980mv and you KNOW you're way too rich.

.870-.910mv and you have a good idea that you're at least in the ballpark. <img src="gr_images/icons/cool.gif" border="0"> You can pretty safely assume that major power gains are not to be had from a better mixture. Some? Maybe. Alot? Not likely.

 

Colonel made the point even better.

So yes there is some value.

PCM will adjust fuel and that will affect WOT.

 

Im a little confused, i didnt think the O2 sensors were used at WOT, is that true? and if so, how can they affect WOT? does the computer sort of remember that you are lean (or rich) and take it a little the other way?

 

FREAK, PCM doesnt use o2 readings WOT, but they are saying it is influenced by what computer learns in normal closed loop operation. So yeah it does sort of remember.

 

AND it give YOU a reference. <img src="gr_grin.gif" border="0">

[ January 16, 2002: Message edited by: zombiedude ]</p>

 

And, although the O2 sensors aren't directly used by the ECM at WOT, the readings are still reported to the ECM and can be read via Autotap or other diagnostic scan tool.