What voltage should I be getting at cruising, hard throttle, wide open throttle, and normal acceleration from the O2 sensor? I have a 1990 LB9 (305) TPI with 5 speed. I have an Ed Wright (Fastchip.com) stage 2 chip (Partial throttle settings have been changed) .I have an auto meter air/fuel ratio meter, and I'm curious to know if anyone can give me a guide as to what I should be seeing.

 

Closed loop - O2 volts will fluctuate from either side of 450mv. It should fluctuate all the time. At wide open throttle (WOT) and startup situations, the O2 sensor is ignored ny the computer and will not fluctuate. At WOT, you should be way over 450 towards 900 (rich side), but you cannot tune by the O2 sensor. It is only a rich/lean switch. You really can't accurately determine how rich or how lean.

 

.850-.900V at WOT sill give you the correct air/fuel ratio. Part throttle crusing will be a varying voltage.

------------------
89 Transam GTA, 350TPI, auto, 3.27 rear, dual cats, gray.
Magnaflow cat-back,
K&N open element,
Best E.T. 14.63@95mph

 

Thanks guys. At partial throttle and cruising, I'm mostly way lean at or below .450 mostly below, and it will jump up to stoichiometric readings shortly and then back down to and past .450. When I floor the accelerator, it only goes to about .800 to .850 indicating a rich mixture. If you can't tune by the O2 sensor then how should I tune it?

 

The o2 sensor is a pretty good tuning tool as long as you know it's only accurate around 14.7:1 afr. At wot, 12.x:1 afr is desired and this should drive it high and it should stay there. It's good for tuning part throttle and plug cuts are good for wot tuning. As long as the o2 keeps switching back and forth you're in the ballpark at light cruise. This could tell you to pull a little fuel out of the maps. You could push timing up also. It's kinda hard to explain and you could damage the motor if you get carried away but as long as you go in small increments and not get detonation at light throttle.... Switching around rich lean at medium hard accell and switched fully rich at wot and staying lean and mean at light throttle all while running the least amount of timing past the point advancing it stops showing gains is how the tuners get such great mpg's.

Hope this didn't cause more confusion...

 

Thanks Joel!!

 

O2 is a fine tool, but in most performance
appz, long tube headers wont be true judge.
the farther the O2 moves from the stock
postition the cooler the charge becomes.
and false reading occur. you will be able
to dial it close and do the rest from plug checks.
another would be from a scanner. watching the
block learn and fuel integrator can show how
the A/F ratio is being commanded. generally
from a stock the 1800-3500rpm range is too
fat in fuel, and the timing is slow.....
airdeano