Figuring out A/F ratio by looking at 02 sensor output?

[Ruffellbaker]

My SCT tuner should be here tomorrow. They called me and said they cant tune my car for the MAF sensor I have which is the JET power flo and said to put the stock one back on just to be safe. The only reason I ordered the tuner is because I have 24lb injectors and was checking my 02 readings with a scan tool and my reading were all high everywhere but at idle. I think it was about 730mv at 2500 rpm which is pretty rich. Does anyone know of a chart or graph that lets you convert 02 sensor output to A/F ratio? I just wanna make sure that the MAF I have isnt causing my tune to be off when I get it.

 

[Noobz347]

From and OEM narrow band sensor? No... not possible. You'll be able to tell whether it's out of range high, out of range low, or in range. That's pretty much it.

 

[Ruffellbaker]

Alright, I guess Ill just have to make a couple pulls with my scan tool after the tune and see if its close.

 

[trinity_gt]

This is what wideband O2 sensors were developed for.

The output of a typical narrow band sensor is like this:

The size of the voltage swings occurring right around 14.7:1 and the plateaus on either side mean the sensor is really only good for rich/lean approximations. You can see that the sensor output could, in theory, change almost 600mV for little change in AFR. This is not usable for real AFR monitoring.

My suggestion: Consider a wideband setup like that from Innovate. Their LC-1 can do two very important things:

1) It can drive a proper AFR meter giving you the actual ratio.

2) It can provide a "simulator" output to drive the vehicle's PCM. This output looks like a narrow band sensor to the PCM so the fuel control using the factory PCM remains. See page 17 of the LC-1 manual:

http://www.innovatemotorsports.com/support/manual/LC-1_Manual.pdf

The nice thing about this setup is that the WB sensor can screw into the downpipe at the factory S1 location and give both WB and NB functionality. There's no need to weld in an additional bung, drill holes in the DP etc...

Real, proper tuning and monitoring can't be properly done with a NB setup.