interpreting the O2's. What does it mean?

[qwiketz]

I hooked up datamaster and now have measurements of my o2's. I have a basic knowledge of where my car should be air/fuel wise. How do I figure out how my car is doing using the o2's. I see super low numbers when putting around town and I have seen super high #'s when my I would get on the throttle from a stop. I know that I should be about 850 for my combo at wot, but how rich is 900, 950, 1000, 1050, and 1100 for that matter? How lean is 800, 750 and 700? thanks!

[Alvin]

On a LT1/4 car I shoot for late 800 mv at wide open. On the L98's its much harder to get accurate O2 readings. That has been my experience.

[qwiketz]

but what does it really mean? Is there any correlation between o2 reading and afr?

[Alvin]

late 800's is typically a hair less a than 13.0

[qwiketz]

cool. Thanks for the info. I was told to shoot for 850's by a couple people for my blown app.

[Alvin]

you definately don't want 850 for a blower car, you want about 920.

[tjwong]

Ideally if you can afford a WBO2 system for your tuning needs, that is the best way to do it. Not to mention the safest way

[Alvin]

agreed, blwoer cars are sensitive to tuning both in AFR and spark.. its harder to fudge (about right) types of fueling into them and have them run 100%

[gbody5]

Originally Posted by Alvin

On the L98's its much harder to get accurate O2 readings. That has been my experience.

I'll do several part throttle and WOT scans and will get different O2's each time. Sometimes upper 800's other times low 900's. Very load sensitive from what I can tell, I pretty much rely on BLM's and knock retard to tune.

[Atok]

Here's a chart that may help:



Unless you use a wide band O2 sensor, the accuracy of the typical O2 sensor like ours is not good out at each end of its range. As you can see it's not a linear sensor and it's designed to be most accurate around 14.5 - 14.7 AFR to help control emissions.

For power tuning I think a wide band O2 is the only way to go. You can buy one complete or build one using a Honda sensor if you're comfortable with electronics. 92-95 Honda Civic, 1.5 VTEC, part # 36531-P07-003. If you're interested, I've got full schematics of a DIY system using this sensor.

Here are some links:

http://www.techedge.com.au/vehicle/wbo2/wbfmd.htm

http://lists.diy-efi.org/mailman/listinfo/wbo2

Look at the "WB" files here:
ftp://ftp.diy-efi.org/uploads/

[scorp508]

I also believe (and I'm sure Alvin would agree) that there is no perfect science that a given ### O2 mv = ##.# AFR. You can get it close, but it isn't dead on. This is especially true with the narrow band junk we're stuck with by default.

It is best to learn what your car's values mean. You can kind of do this on a dyno with a wideband O2, but understand that real world conditions will make things leaner once you're dealing with wind resistance & the weight of the car against the drivetrain.

[Mo_Bandy]

running alky water injection too it will skew the o2's a bit also I have seen cars perform better "fatter" as compared to another.. in CA we have the luxury of 91 octane :P

MO

[Atok]

Originally Posted by scorp508

I also believe (and I'm sure Alvin would agree) that there is no perfect science that a given ### O2 mv = ##.# AFR. You can get it close, but it isn't dead on. This is especially true with the narrow band junk we're stuck with by default.

Yes, WB is the only method accurate enough. The chart I posted above is typical, not exact for all sensors.

[Alvin]

Yep,

Like I said, I've notice them being quite a bit more consistant and relieable in the dual sensor LT1's.

[Dan Parker '96]

You have such limited information with narrow range O2s that the only thing you'll be able to tell is if you're above or below 14.7 air to fuel.

This is consistent with the design of the sensor. It is basically a switch (off/on). Not a lot of play in between.

For instance, the last time I was at the dyno (with new O2s) the sensors read 980mV at 12.8 AFR (according to the wideband). They also read 980mv at 9.5 AFR.

For comparison there was another buddy there with almost exactly the same setup I had and his O2 readings were significantly different than mine at similar wideband readings. They were "in the ballpark" but nothing you could reasonably use for fine tuning or comparison.

I guess you could use a narrow band O2 reading of 800-1000mV to say you're in the 13:1 all the way to 1:1 AFR range. You can't tell reliably.

The design of the narrow range O2 acts like a switch. And it performs that function very well.

You really need a wide band O2 setup to truly fine tune.