O2 Sensors and A/F Ratio
 

I and trying to figure out what the A/F ratio is based on a voltage reading from a O2 sensor

So far I know that a reading of.1 volt is lean and .9 volts is rich.
14.7 : 1 is at .45 volts.

Anybody know what is the optimal ratio (I think 13:1) and what would that equal in a voltage reading from the O2 sensor?

I picked up this package called digimoto and it is for reading different sensors from the ODBII port... also has a built in dyno feature... kinda neat diagnostics software, also reads and clears codes.

OK found some stuff if anyone is interested...


0.97V - 12.1:1 - Very Rich.
0.88V - 12.7:1
0.78V - 13.2:1
0.69V - 13.8:1
0.59V - 14.4:1
0.49V - 14.9:1 - (Stoich-)
0.39V - 15.4:1
0.30V - 16.0:1
0.20V - 16.5:1
0.10V - 17.1:1 - Lean

Stoich is 14.6:1

I would not consider very rich 12.1

Any reason you are trying to figure this out? Maybe we can point you in the right direction

I have a hardware/software package that allows monitoring of sensors through the OBDII port. Just want to gain the information to understand the data when I start looking at it... and of course to possibly tune the engine with a handheld tuning device like SCT or DIABLO.

And yes I know you guys do that stuff and will consider that option down the road as well.

Cheers!

You will not be able to monitor A/F with a stock 02 Sensor or accuratly by monitoring V

'Best bet is a wideband commander or LM-1

Yep! 12.1 is not RICH! have to agree there! on both get a Wideband for a accurate reading! LM or even WMS

So if these sensors are not accurate and you tune the car how is the tune accurate?

Do you make use of the factory sensors for tuning or do you put a different one in to tune... I'm confused?

What good is a tune if it still uses the factory O2 sensors?

the O2 sensors on the car work fine for what they are meant for, which is a very narrow range around stoch, or 14.7:1

that being said, to tune properly, you need to put a wideband O2 sensor in one of the pre-cat bungs to get proper readings.

So is that just for tuning? Do you take it out after it's tuned or leave it in?

Still trying to understand the whole process.

If you take it to get it tuned, they usually have a a/f meter whick they put down your tail-pipe. This is a wide band 02 sensor. They tune with that. They remove it when theyre done tuning the car.

If you buy a wide band 02, then you weld in a bung after the cats or around that area and install the sensor. This remains there all the time as you have a guage and can constanty monitor the a/f reading.

Some dyno shops will weld a bung in and install the sensor and simply remove it and plug it when done.

OK, I still go back to my original concern or question, if the stock O2 sensors are not capable of the readings a wideband sensor is how can you accurately keep that tune if the computer see the stock O2 sensor readings? :banghead:

fir tuning, we use a wideband Sensor. It measures from 6-10

6-10 ? volts?

meant to say

6.0:1-17.0:1 A/F

The bung, O2 is positioned/welded in before the cats, not after.

Your right. i mixed it up! thanks! :tup

I've mixed plenty up myself..numerous times! :cheers:

Factory O2 is a narrow band oxygen sensor, the factory computer only cares that it switches back and forth, from .8 or so to .2 or .3 and that it doesnt stay to one extreme or the other for to long. It uses that to make sure it is opperating in it's programed parameters. When we use a wide band O2 we are reading so as to adjust the parameters in the computer (not really concerned with factory O2's at that point) so we need to actually see where we are at for acutal air/fuel. As for wide band o2 sensors, I personally would test with one if I was playing with my tune (ie. on Pred or SCT) and remove it when just driving around. Wideband sensors have a limited life and are fairly expensive to keep replacing.
O and most widebands read to much higher than 17.0:1

Thanks, good information. So what would you say the factory sensor is good for as far as fuel ratio? 12- 16 or ???

Widebands aren't that expensive anymore. You can get them for $50 now.

The factory sensor wont tell you mixture per say(bouncing to much) the main thing is to ensure it is switching and not pegged at .1 volts (VERY lean)

Where can you get a wideband for $50?

Thanks! I'll do some data logging when she back on the road... hibernating right now :cry2:

Can anyone answer this question??? ^^^^^^^^^^^

Sorry. He was talking about a wide band 02 sensor itself. not something like the lm1 or anything. just the sensor.